To Know a Fly

For last week’s Well-Nigh Wordless Wednesday, I shared a photo of a fly that a lot of people in my city think is a bee.  I can see why people think it is a bee because it’s got that bee-like coloration, but to me the insect all but screams “I’m a fly!”  Nature can be tricky sometimes, especially among the insects.  Thousands of insects look a lot like other insects, many mimicking stinging, biting, or poisonous insects for protection.  Today I’m going to go through the things you should look for to be sure an insect is actually a fly.  This is a fly:

fly in house

A fly, specifically a cactus fly (Copestylum isabellina)

There are several things to look for to determine whether something is a fly or not.  Let’s first consider the name of the order that the flies belong to: Diptera.  As is so frequently the case in biology, the name tells you a lot about the insects within the order.  The prefix di- means two and -ptera refers to wings.  Thus the order Diptera contains insects with two wings, the defining characteristic of the group.  Most insects (with a few non-fly exceptions, including the bizarre order Strepsiptera and some scale insects) have four wings in the winged stage.  Some insects, like the bees and some butterflies, have special structures that hold the fore and hind wings together so that they can look like they only have two wings at first glance (tricky!), but they have four if you look closely.  The flies don’t have hind wings at all!  Instead, they have these little knobby things:

Crane fly halteres

Crane fly

I talked about these structures, called halteres, in a previous post so I won’t say too much about them here.  Briefly, the halteres are remnants of the hind wings in flies and act as gyroscopic organs to tell flies how they are positioned in the air as they fly.  The halteres are likely the reason flies have such amazing control over their flight.  All flies have halteres, though sometimes they’re hidden under the wings and hard to see.

So, adult flies have two wings and two halteres.  Most other adult insects have four wings or no wings and no halteres.  Easy, right?

Not always!  Sometimes it’s hard to get a good look at the wings so that you can count them.  Luckily, the eyes can often provide a clue to whether an insect is a fly or something else.  Flies tend to have very large eyes that wrap around the front and/or sides of their heads, sometimes even meeting in the middle:

fly eyes

Fly eyes

You’ve tried swatting flies, right?  It’s pretty hard to do!  Not only are flies expert fliers, but they also have those giant eyes.  They can see you coming at them with a fly swatter and move out of the way before you squish them.  Not all flies have giant eyes like the fly in the photo, but most of them do.  Bees and wasps tend to have smaller eyes than flies, which can help you distinguish the two groups.

Flies often have strange antennae too.  These are called aristate antennae:

aristate antennae

Aristate antennae

For the most part, if you see an insect with large eyes and antennae like this (with a large, pouch-like structure with a bristle coming off it), you’re looking at a fly and not a bee or a wasp.  This is a rather typical fly with large eyes and aristate antennae:

fly aristate antennae

A fly with large eyes and aristate antennae

Not all flies have aristate antennae though.  Many of them, such as the crane fly, have longer antennae.  Flies tend to have short antennae compared to other insects, however, and they are often very complex in structure.  Bees and wasps have longer, simpler antennae than flies, making the two groups easy to tell apart.

Finally, flies generally have mouthparts designed for sucking liquid food.  The variation in mouhtparts among the flies warrants its own post though, so I’m not going to go into detail here.  If you’ve ever been bitten by a mosquito or a horse fly or watched a house fly lap up food off a dirty plate, you have an idea of how some of the fly mouthparts work.

I want to end this post with a bit of trivia.  Ever wonder why a crane fly, a flesh fly, or a hover fly is considered a true fly while a mayfly, a dragonfly, or a stonefly is not?  They all fly, but they’re not all flies.  Take a close look at how I spelled those names for a hint!  According to traditional entomological naming practices, a true fly in the order Diptera has the “fly” part of its common name separated from the rest of the name while things that are not true flies have the “fly” part tacked on to the end.  Thus, a crane fly is a true fly while a dragonfly is a flying insect belonging to an order other than Diptera.  This distinction is muddled a bit these days with people changing how the names are spelled here and there, but for the most part this trend still holds.  Next time you see the word “fly” separate from the rest of a name, you can be pretty sure that the author is referring to something belonging to the order Diptera and not some random flying insect with four wings.  Consider my favorite quote from Shrek:

“You mighta seen a house fly, maybe even a superfly, but I bet you ain’t never seen a DONKEY FLY!”

If you follow the traditional entomological naming format, one would have to assume from this quote that Donkey is a true fly, NOT a donkey!  To indicate that Donkey is not a fly and is in fact some other flying creature, he should technically be a Donkeyfly.  :)

For more information about flies, I highly recommend Morgan Jackson’s wonderful blog, Biodiversity in Focus.  He takes much better fly photos than I do and his love for flies oozes out of his writing.  Be sure to check it out!


Unless otherwise stated, all text, images, and video are copyright ©

Predaceous diving beetles and water scavenger beetles – What’s the difference?

It’s been a while since I’ve done an identification post, so it’s time for a new one!  Today I’m going to focus on two aquatic beetle groups that a lot of people have a hard time telling apart from one another: the predaceous diving beetles (family Dytiscidae, the dytiscids) and the water scavenger beetles (family Hydrophilidae, the hydrophilids).  Once you know exactly which parts you should be looking for it’s easy, so let’s jump right in!

For these two groups of beetles, you really need to look at some body structures to properly ID them.  This means it’s a whole lot easier to ID them if you take them out of the water for a close look.  However, the body shape may give you a clue.  Let’s look at the dytiscid first:

Dytiscid lateral

Dytiscid, side view

The dytiscids are extremely streamlined and smooth.  Notice how the top of the beetle is rather domed?  And how the bottom is rounded?  These are characteristics of most of the dytiscids that allow them to swim very efficiently.  If you cut one in half across the middle of the abdomen, the shape of the cross-section would be nearly oval.  Now compare this to the hydrophilid:

Hydrophilid lateral

Hydrophilid, side view

The hydrophilids are also streamlined and smooth, but they are a different shape.  Notice how the underside of the beetle is mostly flat, compared to the broadly rounded belly of the dytiscid.  Also, you can’t see it in this view, but the beetle is shaped like an inverted V  or U along the abdomen so that the eltyra slope down away from the center line of the bug like the keel of a boat.  If you cut one of these beetles in half, it would be roughly triangular of semi-circular in cross-section.  So, the dytiscids tend to be very curvy while the hydrophilids are more angular and have some flat edges.  This doesn’t hold true for every member of either group, but it is a general trend.  With practice, you’ll start to notice general body shapes that will let you identify them without taking them out of the water.

Now let’s flip the beetles over for a moment.  First, I’ll draw your attention this structure:

Hydrophilid spike

Hydrophilid spine

Many hydrophilids have a long, sharp spine that runs down the center of the thorax and over the base of the abdomen.  It can be thick and heavy like this one or long and slender.  Not all hydrophilids have these spines, but if you see the spine, you can be sure that it is a hydrophilid and not a dytiscid.  Dead giveaway!  But let’s pretend for a moment that this beetle is one of the hydrophilids that don’t have a spine.  Then we need to look at a different part.

As you probably know, the abdomen and the thorax of insects are made up of several subsections.  The thorax is made up of three sections, with one pair of legs attached to each.  The abdomen is historically made up of 11 sections, but many insect groups have combined sections and now have less than 11.  The first section of the abdomen directly behind the thorax (also called A1) is an important section to look at when identifying beetles because it helps you determine which of the four suborders the beetle in question belongs to.  Dytiscids belong to the suborder Adephaga while the hydrophilids belong to the Polyphaga, so their A1 sections look different on the underside of their bodies.  Let’s look at this section on the hydrophilid first:

Hydrophilid A1

Hydrophilid A1

I know it’s hard to see in the photo, but the legs of this beetle sit on top of A1 and do not split it into two parts.  You can follow the line of the A1 section closest to the back end of the beetle across the entire beetle without interruption.  The dytiscids are different:

Dytiscid A1

Dytiscid A1

Their hind legs break the A1 section apart so that part of the section lies on either side of the legs.  In these beetles, you cannot follow the line of A1 closest to the back end of the bug all the way across the beetle without interruption because the legs get in the way.  If you look closely at the photo (which is admittedly not as clear as it could be), you can see the first section of the legs (those two little bumps the rest of the legs are attached to) extending beyond the A1 section and the two parts of A1 on either side.

It’s going to be impossible to figure out whether a beetle swimming in the water has a broken or unbroken A1.  Even if you scoop the beetle out of the water though, this structure can be difficult to see, especially on some of the smaller beetles.  My students have a very hard time with this characteristic and a lot of them never quite figure it out.  This is where the antennae come in handy!

The antennae of dytiscids and hydrophilids are very different, so it’s easy to tell the two apart.  Finding the antennae on these beetles is an entirely different matter though!  Insect mouthparts have a lot of little dangly bits called palps and it just so happens that a lot of aquatic beetles have their palps sticking out right where you’d expect to see antennae.  Let’s take a look, starting with the dytiscid.  This is not an antenna:

Dytiscid not antenna

Dytiscid, not antenna

Nor is this:

Dytiscid not antenna

Dytiscid, also not antenna

The hydrophilids aren’t any easier.  This is definitely not an antenna:

Hydrophilid, not antenna

Hydrophilid, not antenna

Nearly all of my students eventually try to run through the identification key using these parts and invariably end up in the wrong place, especially with the hydrophilids.  I don’t blame them!  The palps in both beetle groups are in the right place to be antennae and look a lot like what you’d expect an antenna to look like.  In my experience, aquatic beetles are sneaky buggers and like to hide their antennae, especially if you preserve them for a collection or for identification later.  You frequently find them folded down under their heads alongside the inner margin of their eyes.   This is definitely true in the dytiscid pictured above.  I pulled the antenna out so you can actually see it in this photo:

Dytiscid antenna

Dytiscid antenna

See why I say they’re sneaky?!  These antennae look a lot like the palps, only longer.  The antennae of dytiscids are filamentous, which means that each segment of the antenna is about the same length and width as the segment before and after.  Now let’s compare that to the hydrophilid antenna:

Hydrophilid antenna

Hydrophilid antenna

Hydrophilid antennae don’t look anything like the palps!  They have clubbed antennae, which means that the segments near the tip of the antenna are much wider than the ones near the base.  This means that the antennae of the hydrophilids look absolutely nothing like the antennae of the dytiscids!  If you’re looking at the right part, the actual antennae and not the palps, it is very easy to tell these two beetles apart.  Clubbed antennae = hydrophilid.  Filamentous antennae = dytiscid.  Simple!

You often need to look at a combination of these characters to be sure you’ve correctly identified one of these beetles, but it’s not too bad when you know what to look for.  I’ll end the post with a handy dandy chart summing up what I covered above.  Happy identifying!

Characteristic Dytiscidae
(predaceous diving beetles)
(water scavenger beetles)
Shape of cross-section of abdomen Approximately oval Approximately triangular or semi-circular
Spine along center of thorax Never has spine Spine often present
A1 segment Split into 2 parts by legs Continuous, not split by legs
Antennae Filamentous Clubbed


Unless otherwise stated, all text, images, and video are copyright © 2011

Damselfly Taxonomy Fail

People who know me in person learn one thing soon after they meet me (assuming they don’t know already): how to tell damselflies and antlions apart.  Even friends and relatives who have no interest whatsoever in insects still know how to tell these apart.  This is because the general inability of people to distinguish these two insects is one of my biggest pet peeves.  It really shouldn’t bother me – after all, the ratio of entomologists to non-entomologists in the world is probably tiny and I certainly don’t expect everyone to know more than a handful of basic facts about insects – but it bothers me nonetheless.  It bothers me so much, in fact, that people quickly learn the difference if they spend time with me.  It might have something to do with the fact that I loudly point out every instance of misidentified antlions masquerading as damselflies or dragonflies that I see.  This wouldn’t be such a big deal except that I see this mistake ALL THE TIME!  Drives me nuts, and the people who are with me when I rant about how antlions and damselflies aren’t the same thing tend to pick up on the differences really fast.  I think it’s a defensive mechanism.  If someone shopping with me preemptively points out an antlion misidentified as a damselfly, I am less likely to make a scene and embarrass them.  :)

I’m sure the vast majority of people in the world wouldn’t even notice how often antlions are mistaken for damselflies on products.  The only reason I notice is because I happen to really like damselflies and dragonflies and I actively seek products depicting them.  As an entomologist, people also give me insect gifts all the time.  Because I love odonates, I get more odonate gifts than anything else.  But not all of them actually depict dragonflies.  These are a small handful of things I’ve been given that had the word “dragonfly” somewhere on the label:


This was a wedding gift from one of my husband's friends.


I got two of these glass plates from my mom for my birthday in 2009



My sister gave me this shirt a few months ago. I'm thrilled that outdoor clothing maker Columbia is using insects in their designs, but...



One of my best friends' moms gave my husband and me two of these hand towels for our wedding.



This was the first thing my husband gave me after we started dating. He didn't know better at the time.

Did you notice what all of these things have in common?  If you didn’t, here’s a close up of the offensive body part:



Look at those antennae!  Big, long antennae!  Damselflies and dragonflies have short, bristly antennae.  They’re basically little hairs that stick off the front of their heads.  No adult odonates have long antennae, so as far as I’m concerned, none of the insects depicted in the items above are damselflies and are all antlions instead.  It might say “damselfly” on the label, but the people who named these products are wrong.  Wrong wrong wrong!

This pet peeve of mine is so stupid.  I don’t really care what insects are on the things people give me.  I will display nearly any insect in my home.  I am just as happy with things that have antlions on them, long, showy antennae and all, as I am with things with damselflies and dragonflies on them.  Antlions are fabulous insects worthy of being included on products for people to buy.  And I like every one of the gifts pictured in spite of the misidentification.  After all, someone I care about bought me something he or she thought I would like.  I’m darn well going to like it!

I also realize that antlions and damselflies look so similar that most people aren’t even aware that they’re two different animals.  Artists who make odonate images often don’t draw from life and assume that odonates have antennae like most other familiar insects.  It’s not a bad assumption.  Unless you’re an entomologist, there’s very little reason why you might be taught the difference between damseflies and antlions.  Still, it gets to me every time I see an antlion labeled as an odonate.  Ultimately, it all comes down to that label, the proof that the person designing the product doesn’t know what they’re putting on a t-shirt or assumes that the consumer won’t notice the difference.  And the really stupid part is that if there was no label identifying it as a dragonfly or damselfly, I wouldn’t even care! Like I said, the pet peeve is really stupid.  Wish I could get over it.  I welcome suggestions for how to do so!

Before I end my little odonates-don’t-have-long-antennae rant I just want to point out a few things.  Damselflies and antlions might look similar, but they are really nothing alike.  Odonate nymphs are aquatic while antlion larvae bury themselves in sand.  Odonates fly during the day while antlions fly at night.  Odonates can’t fold their wings flat over their backs while antlions can.  Antlions are holometabolous while damselflies are hemimetabolous, so they’re not even remotely closely related.    In fact, they are so distantly related that they have a taxonomy fail index value (as defined by Myrmecos) of 67.02.  That means that this misidentification is almost 3 times as bad as mistaking an opossum for a cat!

I imagine that all of you will now start noticing antlions misidentified as odonates.  Welcome to my world!  You will find them everywhere.  And if you ever happen to hear a loud woman in the next aisle complaining about long antennae on a damselfly shirt that she would have bought except she can’t bring herself to do it thanks to the misidentification, come say hi.  It’s probably me.  :)


Unless otherwise stated, all text, images, and video are copyright © 2011

Mayflies, Damselflies, and Stoneflies: What’s the Difference?

I haven’t done an identification post for a while, so its high time that I write another one!  I find that a lot of people have a hard time distinguishing the aquatic insect nymphs with tails sticking off the back, the mayflies, the damselflies, and the stoneflies.  They’re easy to tell apart once you learn a few basics!  A lot of people have read my post on how to tell the damselflies and dragonflies apart as nymphs, so let’s start with them.

Behold, the mighty damselfly:

damselfly nymph

Damselfly nymph

There are several things to look for that will let you know this is a damselfly nymph and not a stonefly or mayfly.  However, the mouthpart is a dead giveaway!  If you don’t know about the awesome odonate mouthpart, allow me to enlighten you.  Odonates have highly adapted mouthparts that form a long, hinged structure that they can thrust out toward prey to capture it and draw it back to the chewing mouthparts to be eaten.  There are pictures of this structure available on the post linked above and you can see a little part of it sticking out past the head of the damselfly in the image above.  Odonates are the only insects that have this style of mouthpart, so if you have a nymph with tails sticking off the back-end and you can see a long, folded mouthpart under the head, you’re looking at a damselfly for sure.

But perhaps you’re looking at an insect in the water and you aren’t able (or willing) to pull it out to look at the mouthpart – what then?  Well, take a look at the location and structure of the gills:

Damselfly gills

Damselfly gills

The three damselfly “tails” are really gills that they use to help them breathe and swim!  They are always located at the back-end of the insect and they tend to be broad and leaf-shaped with varying levels of pointy-ness.  As you’ll see in a moment, the stoneflies and the mayflies have gills in other locations and do not have broad, leaf-like tails.  If you see gills that look like the image above, you’re looking at a damselfly nymph!

Let’s move along to the mayflies:



You should notice some differences between the mayfly and the damselfly right away.  First, look at the tails:

mayfly tails

Mayfly tails

Nothing broad and leaf-like about these tails!  Mayflies have long, filamentous tails, often longer than their bodies.  They also usually have three tails like the damselflies, but some groups only have 2.  Clearly, the flat-headed mayfly in the photo falls into the latter category.  This causes some confusion when distinguishing the mayflies from the stoneflies, as you’ll see in a moment.  However, if you see 3 filamentous tails, you’ve got a mayfly on your hands!

Now let’s take a look at the location of mayfly gills:

mayfly gills

Mayfly gills

The gills  are always attached along the sides or the bottom of the abdomen in the mayflies, never on the thorax or sticking off the back. If you see gills in another location, you’re not looking at a mayfly.  Mayfly gills tend to be broad and leaf-like as in the damselflies, though they may be fringed or sharply pointed in some groups.  They usually have a pair of gills on nearly every abdominal segment, though the exact placement on the abdomen varies by group.

Now we’re left with the stoneflies:



Stoneflies and mayflies look a lot alike in most cases.  The mayfly in my photos above is a specialized species adapted for living in fast flowing water, but a lot of mayflies are shaped more like the stonefly depicted here.  How do you tell them apart when the body shapes are similar?  Let’s look at the tails first:

Stonefly "tails"

Stonefly "tails"

Stoneflies always have two tails.  Like the mayflies, they’re long and filamentous.  In some species, these tails are very long.  In others, they’re shorter than the length of the abdomen.  They’re never leaf-like.

Let’s check out the location of the gills too.

Stonefly armpit gills

Stonefly gill location

Unlike the damselflies and mayflies, stonefly gill placement is quite variable.  Many species don’t have gills.  Some species that do have gills don’t get them until they’ve matured to some specific point.  Some species have gills on the abdomen, but if they do they’re located only on the first few abdominal segments and never further down.  (This helps distinguish them from the mayflies, which almost always have gills on the 3rd-6th abdominal segments.)  But in most stoneflies with gills, you’ll find them in their armpits, as indicated in the photo.  Stonefly gills are very different from the broad, flattened gills of damselflies and mayflies.  They typically have a round main stalk with multiple branches.  These are called “finger-like” gills for some reason, but I think the structure is rather similar to the boojum tree, just on a smaller scale:

Boojum Tree

Boojum Tree. Photo by Bernard Gagnon, from wiki/File:Boojum_Tree.jpg.

I find that people have the most trouble telling the mayflies and stoneflies apart.  If the mayfly has three tails, no problem!  It’s a mayfly for sure.  However, you have to remember those pesky two-tailed mayflies that throw a wrench in the whole system.  Plus, mayflies are notorious for losing their gills.  If you’re working with preserved specimens, sometimes it’s hard to figure out where the gills did or did not attach.  How then do you tell a two-tailed mayfly with no gills apart from a similarly shaped stonefly with no gills?  It’s easy!  Look at the claws on the legs.  Mayflies have one claw on every foot.  Stoneflies have two.  It couldn’t be simpler.

As with any identification, the more animals you see, the easier this gets.  For those of you who have little experience collecting and identifying insects, getting a specimen IDed to order can be a challenge at times!  Remembering the characteristics of tons of insects can be hard too.  I thus present this handy-dandy chart that summarizes the information I covered above:

Mayfly Damselfly Stonefly
Location of Gills abdomen end of abdomen when present, thorax, base of abdomen
Shape of Gills leaf-like, plate-like, or fringed leaf-like finger-like
Style of Mouthparts chewing chewing + hinged segment folded under head chewing
Number of Tails 2-3 3 2
Shape of Tails filamentous leaf-like filamentous
Number of Claws 1 2 2

If you forget the characteristics of the mayflies, damselflies, and stoneflies, use this chart as a quick reminder of what to look for!

Next up: another thrilling edition of Friday 5!  This week’s will feature 5 places I’ve found a particular type of tiny insect in my home.  Check it out to discover where these little beasts may be lurking!


Unless otherwise stated, all text, images, and video are copyright © 2011

Caterpillar Camouflage

Today I have a short post for you!  I was out collecting with my students during class last week and one of them took us to a nice spot on campus, a secluded little courtyard of one of the old buildings with a handful of citrus trees.  We looked around and found some stink bugs on a tree, some butterfly cocoons hanging off the buildings, and some spingtails.  One of my students found this:

Papilio cresphontes

Papilio cresphontes

If you think this looks like something that was ejected from the back end of a bird, you’re not alone!  This is the caterpillar of the giant swallowtail (Papilio cresphontes).  As you might imagine, looking like bird droppings has its advantages.  This caterpillar blends very well into the background and it is hard to recognize that it is an insect at all.  That’s the whole point of looking like bird droppings!  Any insectivore (an organism that eats insects) looking for a tasty caterpillar to eat is likely to pass right by this one because it looks so much like something else – and something most animals wouldn’t consider eating.  The appearance of this caterpillar is part of its defense against predators.  If it stays still, most predators won’t even notice it’s there.

But say something happens to bump into the caterpillar (such as an insect systematics student looking for insects for her collection) or otherwise detects the caterpillar’s presence.  Then the caterpillar brings out it’s backup defense!  It’s depicted in this video:

That little orange slimy looking thing that pops out of the caterpillar is called an osmeterium.  Normally, it’s hidden in a pouch inside swallowtail caterpillars, right behind the head.  When disturbed, the caterpillar can squeeze some of it’s hemolymph into the osmeterium, causing it to pop out of the pouch.  The everted osmeterium is then waved at the predator.  Now how might this little organ be useful in deterring predators that might want to eat the caterpillar?  It’s covered in potently stinky chemicals!  Any animal that gets a big whiff of a foul smelling substance from something it’s considering eating, especially from something that looks a whole lot like bird poop in the first place, is probably going to pause for a moment and consider whether it’s worth eating.  Most things will leave the caterpillar alone rather than eating it.  And when the predator wanders off and leaves the caterpillar to itself, it can pull the osmeterium back into the pouch behind its head until the next time it’s needed.

Pretty fun, eh?  If a caterpillar that looks like bird poop isn’t fun, I don’t know what is!  :)


Unless otherwise stated, all text, images, and video are copyright © 2010


Where to look for dragonfly identification information

A lot of the people who have sent me dragonfly swarm reports have expressed an interest in identifying the dragonflies they’re seeing in their yards.  I think this warrants a post on where to find information about dragonfly identification!  Today I’ll cover some of the books I really love and some of the best online resources you can use.  I’ll also tell you what you can do if you’re stuck and need the advice of an expert to help you figure out the dragonflies that you’ve seen.  I’m a scientist, so I have a lot of technical books that I can use to help me identify dragonfly species very precisely using a microscope and other special tools, but this post is meant to help people who are not dragonfly experts to find accessible information.  I hope you will find this useful!

Dragonflies Through Binoculars cover

I am a huge book lover, so I personally turn to books whenever I want to ID a dragonfly or damselfly that I’ve seen.  I have several favorites, but I use two over and over again because they are so thorough and include ALL of the species in a particular area.  Dragonflies Through Binoculars by Sidney Dunkle is a great source of information about the North American dragonflies.  It includes photos, descriptions, distribution maps, and flight dates for each of the species.  It also does a great job of highlighting the distinguishing characteristics so you can tell species apart even if they are very similar in appearance.  This is a great book and I always take it with me when I travel.  The only downsides are that the book doesn’t include the damselflies and it it now 10 years old, so some of the information might be slightly out of date.  The book I turn to again and again when I want to have all of the dragonflies and damselflies in one place is Dragonflies and Damselflies of the West by Dennis Paulson.  This book shares all of the great features of Dunkle’s book, but it is is newer and includes the damselflies.  I LOVE the behavioral information in this book!  However, if you live outside of the western part of the US and Canada, this book isn’t going to be as useful.   Luckily, dragonflies are popular, so there are a lot of great resources out there!  Your best bet is getting on Amazon and searching for either dragonfly or odonata and your state or country.  There are tons of local guides available, so it’s definitely worth looking for one for your area!

odonata central screen capture

There are several great online resources, but I am particularly fond of Odonata Central.  Odonata Central is an amazing website!  It include up-to-date information about flight seasons, distributions, characteristics, etc.  Even if you know nothing about the dragonflies you’re seeing, Odonata Central is an excellent resource.  For example, to see a list of every species in your area, you can click on the checklist link at the top of the page.  The website will guide you to your location (in the US, you can get information for your county) and a list of all of the species in your area will appear.  You’ll also see links for photos, maps, and information about each species on the list.  By clicking through the images and reading the descriptions, you will likely be able to identify the species in your area.  The best part: this works for almost any location, including areas outside of North America.

Many, many people (including Odonata Central) have photo galleries of dragonflies online and simply scrolling through photos can take you a long way toward identifying the species you see in your area.  I love the Digital Dragonfly website’s image gallery, though not all American species are included.  Because I live in southern Arizona, I also frequently check websites such as Arizona Odonates and California Dragonflies and Damselflies for photos and identification information.   To find websites with information about your local dragonflies and damselflies, check out the links page at Ode News or the links page at Odonata Central.  They both have comprehensive lists of good, reliable information available online.

Bug Guide screen capture

If, after you have tried the field guides and scrolled through photo galleries, you just can’t decide whether your dragonfly is a neon skimmer or a flame skimmer, where can you turn?  There are two great resources available at your disposal.  The first is BugGuide.  In addition to great photo galleries, you can also submit photos of dragonflies or damselflies and request an ID.  Bug Guide is a network of insect and spider enthusiasts who volunteer their time helping people ID bugs they’ve seen.  When you submit an ID request, one of the many Bug Guide users will likely know which species you’ve seen an give you an ID!  To get the most specific response, take a photo of at least the back and the side of the dragonfly or damselfly as clearly as you can because the characteristics that distinguish species are most often in these areas.  Then upload your photos to the Bug Guide by clicking ID Request at the top of the page and following the instructions.  Most people get responses to their inquiries within a few days.

Did you know that there are entomologists all over the US trained to help non-entomologists identify insects?  Land grant universities are often required to maintain research collections of various groups of organisms (including insects, snakes, fish, crustaceans, plants, etc) and to provide outreach to the public.  If you have a land grant university in your area, you likely have someone who can help you ID insects and provide information about them at the university.   The Cooperative Extension service is the main outreach component of most land grant universities and nearly every county in the US has an office.  The Cooperative Extension service employs a large number of entomologists, so give your county office a call!  If your county’s entomologist can’t ID a dragonfly for you, he or she likely knows a person who can.  And finally, Odonata Central maintains a member directory that includes many dragonfly experts and/or enthusiasts around the world.  If you click on View All at the top of the page and search for your location, you might be able to find a odonatologist nearby who can answer your dragonfly ID questions and give you more information about your local species.  That said, tracking down their contact info might not be easy in every case.

As I said earlier, dragonflies are very popular insects, so there are tons of resources available!  In fact, the volume of information available can be overwhelming if you don’t know where to begin.  Hopefully, this post will direct you to the best resources available and make it as easy as possible to figure out which dragonfly species you’ve been seeing.  Good luck!

I’m getting away from dragonflies for the next few posts, but check back near the end of October for a summary of the results of my dragonfly swarm data collection effort this summer.  I’ve collected more reports than I ever thought I would, so it should be an interesting read!


Unless otherwise stated, all text, images, and video are copyright © 2010

Migratory Dragonfly Species – Less Common Species

Well, my plan to get the less common migratory dragonfly species up last week failed miserably.  I was going to try to get it done before I went on my little Labor Day mini-vacation.  After working 16 hour days for two weeks before I left, I realized that wasn’t going to happen.  ”No problem!” I thought.  ”I’ll bring my materials with me so I can do the post while I’m on vacation!”  Then I forgot to bring most of the things I needed to do the post.  Basically, the plan was doomed from the start!  So, I’m finally back home and once again have everything I need to get the post done.  Sorry for the delay!

The dragonflies depicted and described here are migratory species, but they’re less commonly observed migrating than the ones included in the common migratory species list.  You’ll see these species in swarms, either static or migratory, but you’d want to look here after you look at the pictures of the common species.  They’ll make up a smaller part of the swarm or will not swarm with the same regularity that the common species exhibit.  Still, I thought this would be a useful resource for people who wish to identify the dragonflies they see swarming in or over their yards.

Like last time, let’s start with the big dragonflies, the darners in the dragonfly family Aeshnidae.  This gorgeous animal is the lance-tipped darner (Aeshna constricta):

Aeshna constricta male

Aeshna constricta male.  Image by David E. Reed and from

Aeshna constricta female

Aeshna constricta female, green form. Photo by Larry de March and from

I think the mosaic darners from the genus Aeshna are some of the most beautiful dragonflies and this one is no exception!   Things to look for: Large, 2.8 inches long.  Males with brown thorax with blue stripes on the side.  No stripes on face of male.  Front-most stripe on side of thorax green on half closest to legs, blue on half closest to wings in males.  Bright blue markings on abdomen in mature males.  Females have all markings either blue, bright green, or yellow depending on form.  Females may have orange-brown wing tinting on the half closest to the body, especially in yellow form.  Lance-tipped darners are found in the northern half of the United States and in southern Canada.  You can tell them apart from other migratory mosaic darners in their range based on the lack of stripes on the face and the wedge shaped cerci (those dangly bits hanging off the back).

The other less common migratory darner is this one:

Aeshna eremita male

Aeshna eremita male. Photo from

Aeshna eremita male side view

Aeshna eremita male side view. Photo from

This is the lake darner, or Aeshna eremita. This species looks very similar to the other mosaic darners (including the lance-tipped darner above), but it’s the biggest one in the US and Canada.  Things to look for: Large, 3.1  inches long.  Both sexes with brown thorax.  Stripes on side of thorax blue above and green below with a conspicuous notch in the center (this is very easy to see in the image of the side of the dragonfly at left).  Found in northern United States and southern Canada, with a narrow finger extending southward to Utah and Colorado in the west.  You can tell them apart from other migratory mosaic darners in their range based on the size and the big notch in the stripes on the side of the thorax.

Distinguishing the mosaic darners without catching them can be difficult, even for people who know them well!  If in doubt, try to get a good photo of the top and side of the dragonfly (like the one above) or get as good a look at the color patterns on the abdomen and the thorax as you can.  I’ll tell you where you can send photos or look for good identification information to ID your dragonflies in future post (coming soon!).

The skimmers (family Libellulidae) are much easier to tell apart, especially the migratory species!  This one is very easy:

Celithemis elisa male

Celithemis elisa male. Photo from

Celithemis elisa female

Celithemis elisa female. Photo by Steve Scott and from

This is the calico pennant (Celithemis elisa), one member of a genus of highly recognizable, medium sized dragonflies.  Things to look for: 1.8 inches long.  All individuals begin their adult lives with the yellow markings in the image of the female, but markings become red as males age.  Pattern and coloration of the wings are specific to this single species – if you see this pattern of wing spots, it’s this species.  You’ll find this species across the eastern half of the United States and a very small section of extreme southeast Canada.

Next up we have a dragonfly with a very limited distribution:

Erythemis berenice male

Erythemis berenice male. Photo from

Erythemis berenice female

Erythemis berenice female. Photo from

Meet the seaside dragonlet (Erythrodiplax berenice)!  I’ve had a chance to see this beautiful dragonfly on a trip to visit my sister the Park Ranger and it’s a stunner, especially the females.  Things to look for: Small dragonfly, only 1.3 inches.  Slender bodies.  Males start out with some yellow markings on the top of the abdomen, but these fade to black with age.  No coloration on the male wings.  Females similar shape with yellow markings on top of abdomen.  One female form with the black thorax seen in the males, the other (as seen at left, the spotted form) with a series of black and yellow stripes along the thorax.  Spotted female with brown spots on wings.  Found along the eastern and Gulf coasts and along southwestern lakes with high salt contents.

Now for the king skimmers from the genus Libellula.  The first one is the bar-winged skimmer (Libellula axilena):

Things to look for: medium-sized dragonfly, 2.2 inches long.  Brown thorax and abdomen.  Abdomen with a thick black stripe down the center top.  Males may appear white in some areas as they mature due to prunescence.  Black markings across the upper surface of all four wings.  This pattern is sometimes seen in the slaty skimmer (Libellula incesta), which is found in the same areas and is about the same size.  Distinguish the males by looking at the face: slaty skimmers have a brown face while the bar-winged skimmer has a black face.  Also, the slaty skimmer is not known to be migratory.  Found through the deep south and in the states along the Atlantic coast.

The next king skimmer is this one:

Libellula quadrimaculata

Libellula quadrimaculata. Photo from

This is the four-spotted skimmer or Libellula quadrimaculata.  Things to look for: medium dragonfly, 1.7 inches long.  Wings with black spots along top margin of wings, halfway between base and tip.  Hindwing with a black triangular spot at the base of the wing.  Abdomen brown near thorax and darkening to black near the posterior end, yellow stripes along side.  Both sexes similar.  Common in the northern half of the US, the Four Corners states, and most of Canada.

And the last king skimmer:

Libellula vibrans male

Libellula vibrans male. Photo from

Libellula vibrans female

Libellula vibrans female. Photo from

This is the great blue skimmer or Libellula vibrans.  Note the similarity of the female to the bar-winged skimmer, with which it shares part of its range.  Things to look for: medium-large dragonfly, 2.2 inches long.  Dark black spot along upper margins of wings, halfway between base and tip, and a black streak at the base of each wing.  Tips of wings amber.    Male body pale blue-white with blue eyes.  Females brown with a black stripe down the center of the abdomen, blue eyes.  Distinguish from bar-winged skimmers based on wing coloration patterns and the color of the eyes.  Range throughout southeastern US.

And we’ll finish up with three of the small dragonflies:

Pachydiplax longipennis

Pachydiplax longipennis male

Blue dasher (Pachydiplax longipennis) female

Pachydiplax longipennis female

This is the blue dasher, also known as Pachydiplax longipennis.  Things to look for: Small to medium body, 1-1.7 inches long.  Males pale blue-white, sometimes with black and yellow striped thorax, and bright green eyes.  Females black with yellow markings on body.  May have some coloration on the wings, light brown or amber in color.  Found throughout most of the US except the northernmost states of the west-central section.  The blue dasher is a very common species in much of its range and is often seen at small ponds, such as those found in yards and small parks.

And last but not least, two meadowhawks!  This one is very common:

Sympetrum corruptum male

Sympetrum corruptum male

The variegated meadowhawk or Sympetrum corruptum. This is likely the dragonfly you’re seeing if you see a migratory swarm west of the Mississippi River.  Things to look for: Smallish sized dragonfly, 1.5 inches long.  Body mostly grey with a red stripe down the center of the abdomen.  Red markings wrap around the abdomen as well, demarcating the boundaries of the abdomen’s subsegments.  Abdomen also has a series of small, white spots along the lower edge of the side.  These spots are more prominent in the females than the males.  Females replace the red markings with yellow on the abdomen.  Both sexes may look tan as they fly.  Found throughout the western half of the US and southwestern Canada.

And finally, the ruby meadowhawk (Sympetrum rubicundulum):

Sympetrum rubicundulum male

Sympetrum rubicundulum male. Photo by Stephen Cresswell and from

This species unfortunately looks nearly identical to another meadowhawk (the cherry meadowhawk, Sympetrum internum) and shares its range with it, but this species is a known migratory species and the cherry is not.  Things to look for: Small dragonfly, 1.3 inches long.  Abdomen red with black markings on sides.  Wings veins dark (they’re orange in the cherry meadowhawk).  Face yellow or brown (red in cherry meadowhawk).  Abdomen rather bulbous where it meets the thorax, narrows through the center, and expands again toward the back.  Found throughout the northeastern quarter of the US and parts of southern Canada.

And that’s it for the migratory dragonfly species!  Between the common and the less common species, y0u’ll likely find the majority of the dragonflies you might see in swarms in your area.  Next time, I’ll go over what’s known about static dragonfly swarms (feeding swarms) and then I’ll make some suggestions for where to go for dragonfly identification information.  Until next time!


Have you seen a dragonfly swarm?

I am tracking swarms so I can learn more about this interesting behavior.  If you see one, I’d love to hear from you!  Please visit my Report a Dragonfly Swarm page to fill out the official report form.  It only takes a few minutes!



Want more information?

Visit my dragonfly swarm information page for my entire collection of posts about dragonfly swarms!


Unless otherwise stated, all text, images, and video are copyright © 2010