Dragonfly swarm!

I work out on a lake once a week as part of my job.  We’re managing the water quality of the lake, which involves a lot of hot, hard work and heavy lifting in the sun on a metal boat.  Sometimes the job is really awful, especially during the summer when it’s over 100 degrees in the shade and super humid thanks to the evaporation from the lake.  A few days ago, my coworker/friend and I got out to the lake as early as we could to avoid the forecasted 108 degrees.  I’m glad we got there early because we were treated to the most spectacular dragonfly display I’ve seen so far!  Take a look at the video of this behavior I posted on YouTube so you can see what it looked like:

Isn’t it fun to see so many dragonflies flying together at one time?  The swarm was made up hundreds of male dragonflies, all flying over the grass on the hill adjacent to the lake.  There were also several different species making up the swarm.  My friend (also a biologist) and I weren’t sure what the dragonflies were up to, so we speculated about what they might be doing.

One possibility was that the dragonflies were patrolling the area over the grass, protecting a territory they had set up.  Dragonflies, especially the males that made up the swarm, tend to be highly territorial.  You would usually see only one male in an area at a time, unless a male from another area is challenging the resident male.  It would thus be very unusual for so many male dragonflies to be in a single area at the same time, especially a position away from the water.  Dragonflies are known to be tricked into thinking they have found water when they have not on occasion (see my post about dragonflies patrolling over cars), but there was no reason to suspect they were being tricked en masse.  If dragonflies commonly mistook grass for water, they wouldn’t have been around for as many millions of years as they have!  The grass hadn’t been recently watered either, so they likely didn’t mistake it for water because it was wet.

When dragonflies patrol their territories, they tend to exhibit distinct flight patterns, making the same motions over and over again until something (food, mates, competitors) enters their territory and they veer off path to investigate.  The dragonflies in the swarm exhibited erratic, jerking flights, not the controlled, fluid flights of typical patrolling males.  Dragonflies of different species also tend to fly at different heights while patrolling and/or exhibit different flight patterns.  All the bugs in the swarm were  flying at the same height and using the same motions.  With all of these facts in mind, we ruled out patrolling over the grass.  The members of the swarm clearly weren’t patrolling.

We ruled out the possibility that the males were looking for mates for many of the same reasons.  A female dragonfly usually needs water to be able to lay her eggs.  She will fly out over the water, find a place that looks safe for her offspring, and mate with the male that controls that area.  If the dragonflies weren’t mistaking the grass for water, they wouldn’t be looking for mates.  Females wouldn’t come to the area over the grass to mate because the area wasn’t suitable for egg deposition.  So, mating probably wasn’t the reason for the swarm.

We eventually decided this had to be a feeding behavior.  If you looked just right, you could see thousands of little insects flying above the grass.  These little insects were buzzing around all over the place.  If the dragonflies were chasing little bugs that were flying erratically, they would be flying erratically themselves.  Also, there really wouldn’t be any reason why they should be over the grass instead of the water unless there was some benefit to their being there.  Because they find mates at the water, each moment a male dragonfly spends away from the water represents a lost chance for mating.  However, if there were a ton of food available on the hill that wasn’t available over the water, there was a benefit to flying over the grass.  If the food was particularly abundant, i.e. there was enough to go around, it would also explain why the dragonflies were tolerating one another and not chasing their competitors away.  It had to be a feeding swarm.

We collected a few dragonflies from the swarm (MUCH easier to catch in the swarm than as individuals over the water!), watched the swarm for a while, and then got to work.  It was a hot, miserable day on the lake, but my friend and I agreed it had been worth taking the time to watch the dragonflies.  It ended up making up for the discomfort of the work.

I looked into the swarming behavior when I got home from work and learned that it is indeed common for some dragonfly species to fly in large feeding swarms like the one we saw.  Looking into it further, I learned that the four species I was able to identify within the swarm are the ones most commonly known to make these sorts of feeding aggregates.  I hadn’t ever read about dragonfly swarms or seen one before, but it was gratifying to know that my friend and I were able to figure it out on our own, simply by thinking about what we knew about dragonflies and their behaviors.  It just goes to show that the more you know about an insect’s behavior, the better you are able to explain new behaviors you haven’t seen before!  Regardless, I was ecstatic to see the swarm!  It was an amazing experience and one I will remember forever.

In my next post, I’ll go over the species we found and how to identify them so you’ll know some of the species to look out for if you ever come across a dragonfly swarm yourself.  The dragonflies that made up this swarm are easy to tell apart.  In another post, I’ll talk about what we think the dragonflies were eating and the evidence we found for it.  Stay tuned!

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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!

Thanks!

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Want more information?

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

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Text and video copyright © 2009-2010 DragonflyWoman.wordpress.com

Dragonflies and Damselflies – What’s the difference? (Adults)

A couple of posts ago, I went over the difference between dragonflies and damselflies in the nymph stage.  Today I’m going to cover the difference between dragonfly and damselfly adults.  They’re very easy to tell apart once you know what you’re looking for, so let’s drive right in!

This is a dragonfly:

Anax junius adult

Adult dragonfly (Anax junius, male)

A few thing to notice about the dragonfly:

1) The eyes are broadly rounded and lie mostly flat against the head
2) The thorax (the green part the wings are attached to in the picture above) ismore broad than the abdomen (the blue part in this dragonfly)
3) The forewings and hindwings are different shapes
4) Body is quite large (The dragonfly in the picture, a green darner, is about 3 inches long!), though there is a lot of variation in size

All dragonflies share these characteristics.  Also, if you saw this dragonfly sitting on a plant or on the ground, it’s wings would be held in the same position you see in the picture, spread out flat and to the sides of its body.

Now compare the dragonfly picture to this picture of a damselfly:

damselfly adult

Damselfly adult (unidentified sp.)

Look for these things in the damselfly:

1) The eyes are largely spherical and protrude off the sides of the head
2) The thorax (the segment where the wings are attached) is narrow, about the same width as the abdomen
3) The forewings and hindwings are very similar in size and shape
4) Usually fairly small (at least compared to the dragonflies)

If you saw a damselfly resting at a pond, it’s wing would look different from a dragonfly’s.  Rather than holding it’s wings flat and to the sides of it’s body, it holds its wings straight up, pressed together over the top of its thorax.  This is what you would see in the field if you saw one from the side:

damselfly adult

Damselfly adult, side view (Enallagma boreale)

Ultimately, if you’re at a pond or river, the easiest way to tell whether an odonate you’re looking at is a dragonfly or damselfly is to look at how it holds it’s wings while resting.  If they’re lying flat, parallel to the ground, you are looking at a dragonfly.  If the wings are pressed together, held over the bug’s back, you’ve got a damselfly.  So what happens if the odonate you’re looking at doesn’t ever stop flying?  Let’s think back to the difference between perchers and fliers from my last post.  Fliers are almost always dragonflies and damselflies are almost always perchers.  If it doesn’t stop to rest every few minutes, it’s probably a dragonfly.

Okay.  Now imagine you have two pinned odonate specimens, one dragonfly and one damselfly, rather than seeing them in the field.  The wings are spread apart on both.  Can you tell the two insects apart?  We know you should look at the shape and location of the eyes, the width of the thorax, whether the forewings look like the hind wings, and the size of the body.  See if you can tell which one is which in this picture:

dragon and damsel

A dragonfly and a damselfly - can you tell them apart?

The answers are listed below so you can’t cheat!  Scroll down to check your answers.  Hopefully you got them right!

If you have problems remembering the difference when you don’t have a list of their characteristics sitting right in front of you, here’s a good way to remember them.  Think of the names of these insects, dragonflies and damselflies.  What sorts of images do these names conjure in your mind?  I personally think of medieval stories about dragons holding damsels in distress hostage to use as bait for daring knights.  Think of dragonflies as you would the dragon in this image: robust, strong, powerful, and really big.  The damselfly is more like the damsel in the dragon and the damsel image.  They are smaller, softer, and weaker than the dragon.

One final note about dragonflies and damselflies as I finish this up.  The odonates have become very popular with non-scientists recently and dragonfly watching has become a sort of sport similar to bird watching.  With the publication of several excellent field guides which contain all of the species in a region or the country, it is easy for people who are not familiar with insects to identify the dragonflies and damselflies they see without specialized training or equipment.  All you need is a good field guide and a pair of binoculars!  If this is something that interests you, I have two field guides that I haul around with me when I’m out camping, bug collecting, on class field trips, etc, that I would like to recommend.  The first is Dragonflies Through Binoculars by Sidney Dunkle.  The book is about $30 retail (less on Amazon.com) and covers all of the dragonflies in the U.S.  The book contains excellent distribution maps and flight season information, color photos of every species, the common and scientific names for every species, and multiple pictures for species where the males and females (and sometimes the younger males) are different colors.  The descriptions for each species highlights the distinctive characteristics you should look for to tell them apart from other similar species.  It’s a really excellent book.  The downside: no damselflies!  I recently acquired a book that covers dragonflies AND damselflies in the western U.S., Dragonflies and Damselflies of the West by Dennis Paulson, so that I have a field guide for the damselflies too.  It has many of the same features as Dunkle’s book and costs about the same, but includes both dragonflies and damselflies.  The downside to this book: the book doesn’t cover the whole country, so you need another book if you’re going somewhere east of Kansas or Nebraska.  Still, it gets the job done in my area and I find it very useful.  Dragonfly watching is a fun activity and I hope you will give it a try!  There’s nothing quite like the feeling of checking another dragonfly, one you’ve never seen before, off your checklist.

Answer to the dragonfly vs. damselfly quiz above: A is the damselfly (one of the largest in the country!) and B is the dragonfly.

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Text and images copyright © 2009 DragonflyWoman.wordpress.com

Dragonfly sighting!

I was planning on discussing the differences between adult dragonflies and damselflies in this post, but I can’t reist talking about a dragonfly I saw on Saturday instead.  This lovely little dragonfly is Pachydiplax longipennis, also known as the blue dasher:

Pachydiplax longipennis

Blue dasher (Pachydiplax longipennis)

Isn’t he gorgeous?!  Pachydiplax longipennis is a very common dragonfly in the Tucson area, medium sized (a couple of inches long) and usually found perching on vegetation near ponds.  As you can see, the males have a sort of whitish waxy coating over blue bodies (they are pruninose) and they have bright green eyes.  The extent of the pruinosity varies a bit from place to place, but here in Tucson it covers most of their bodies.

This particular male was perching on the bush next to my fiancee’s car (more about why he was near the car in a moment).  Dragonflies (not damselflies – see my next post to learn how to tell the two apart!) are generally split into two groups based on their behaviors.  Perchers, like Pachydiplax longipennis, sit on vegetation near water.  From their perches, they are able to protect their territories from other males, see females that come into their territories, and spot insects and other animals they might want to eat.  When disturbed for any of these reasons, they’ll dart off their perch and fight, mate, or grab their prey, but they spend a majority of their time sitting on their perch watching and waiting for things to happen.

The other group of dragonflies is made up of the fliers.  These dragonflies fly almost constantly, patrolling their territories for mates, aggressors, or prey on the wing.  They rarely stop moving unless they are mating or wrestling with a particularly large piece of food.  You would be hard pressed to get a photo like the one above if this dragonfly were a flier instead of a percher because they rarely sit still that long.

Back to why this dragonfly was near the car.  Dragonflies have amazing vision which they use to find territories, mates, and food.  See those giant eyes that take up almost the entire head of the dasher pictured above?  These are clearly very visual animals.  Dragonfly nymphs are aquatic, so their eggs need to be laid either in or near water.  So, dragonflies need to be able to find the water.  They do this by looking for certain patterns of polarized light as they fly overhead.  If a male finds the right pattern of light, the one that screams “Water!” at him, he’ll set up a territory and protect his patch of the water from other males in the area.  If he’s a percher, he’ll find a nice place to rest nearby and survey his territory from his perch.  Why, then, was this dragonfly near a car?  The clear coating on many cars gives off the same pattern of light as water in ponds.  As far as this dragonfly is concerned, the car is a pond!  He thinks he must protect it from other dragonflies that might be in the area, so he was perched in the bush nearby and watching the area around the car.

This dragonfly exhibited one other behavior while I watched.  This picture is unfortunately not as clear as it could be because he was having a hard time staying still, but you’ll get the idea:

Pachydiplax longipennis obelisk

Blue dasher (Pachydiplax longipennis), obelisk position

This dragonfly is in what is called the obelisk position, sitting on the antenna of my fiancee’s car.  Have any idea why they might rest in this position?  I’ll give you a hint: this photo was taken around noon on a hot and sunny day.  Dragonflies actually use this position as a way to help cool their bodies down when they are overheated.  Dragonflies, like all insects, are cold blooded (=exothermic) and their body temperature closely tracks the temperature of the air.  When it is very hot or very sunny, their body temperatures get too high and they must use a variety of behaviors to cool down.  Dragonflies are pretty unique in using the obelisk position.  Here’s how it works.  Imagine you are out under a very hot sun.  You have two choices of positions: standing upright or lying flat on your back.  Which position should you use to minimize the amount of sun that hits your body?  If you chose standing upright, you’re correct!  By standing upright, the summer noon sun will only hit your head and shoulders, leaving the rest of your body shaded.  If you laid on the ground, half of your body would be hit by the sun!  Dragonflies use the oblesik position in exactly the same way.  By extending their abdomens upwards, instead of holding it horizontally as they usually do (shown in the first photo), they minimize the amount of sun hitting their bodies.  The sun only hits the tip of the abdomen, part of the thorax and head, and part of the wings rather than the entire top surface of the dragonfly.  So, this dragonfly is in this position because he is hot and needs to cool down.  If the obelisk position isn’t enough, he’ll fly into a shaded area, even if it means abandoning his territory for a while.  Defending a territory isn’t worth risking death by overheating.

This dragonfly flew away shortly after I took this photo.  I disturbed him enough that he gave up on defending his “pond” and flew away to look for a place that had fewer dangerous large mammals.  I hope he found a backyard pond instead of another car!  I always find the car thing a little depressing.

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Text and images copyright © 2009 DragonflyWoman.wordpress.com

 

Dragonflies and damselflies – What’s the difference? (Nymphs)

I get lots of questions about how to identify aquatic insects, especially how you tell one apart from another that looks similar.  Most people are able to identify an adult beetle fairly well and the bugs are easy once you know what you’re looking for (see my post on the subject), but  many people seem to have a hard time telling the dragonflies, mayflies, and stoneflies apart.  The students I teach in my Aquatic Entomology class have a hard time with this at first too, so it’s not something that I’d expect most people to know how to do.  Still, it’s pretty easy once you know which insects have which traits.  Today I’m going to focus on the immature stage of the dragonflies and damselflies, the nymphs.  I’ll cover the adults in the next post and the stonefies and mayflies in my post after that.

First things first.  The scientific name for the order to which the dragonflies and damselflies belong is called Odonata.  Entomologists like me often call the insects belonging to this group odonates.  While it might seem complex to use the scientific word, it’s really pretty convenient.  Unlike in some countries, such as England, scientists in the U.S. have different names for dragonflies and damselflies.  It’s thus nice to have a word that refers to both at the same time and the word odonate fits the bill nicely.  If I’m referring to a the dragonflies and damselflies as a whole group, I’ll call them odonates.

The American odonates are divided into two groups, the damselflies (scientific name = Zygoptera) and the dragonflies (scientific name = Anisoptera).  There is a third group found only in limited locations in Asia called Anisozygoptera, but since we don’t have them in the U.S., I’m not going to talk about them here.

Let’s go over what makes an odonate an odonate before we get into the two different groups.  This is what a standard odonate nymph looks like:

Dragonfly nymph

Dragonfly nymph

This is a dragonfly nymph and we’ll get to how to tell it apart from a damselfly in a moment.  Odonate nymphs generally have long bodies, large heads with large eyes, and long, slender legs.  You can see all of these traits easily in the image above.  However, some other things, like mayflies and stoneflies, share some of these traits, so you need to look for the specialized odonate mouthparts if you want to be really sure you’re looking at an odonate:

dragonfly mouthparts top

Dragonfly mouthparts top

Dragonfly mouthparts side view

Dragonfly mouthparts side view

As you can see in the image above, odonates have a long, extendible mouthpart they keep folded up under their heads.  Odonates are predators and eat other insects, small fish, small tadpoles, and other aquatic organisms while they’re nymphs.  This specialized mouthpart is really cool because it allows an odonate nymph to hunt very effectively.  They are able to push the fluids in their body into their heads very rapidly, which causes the mouthpart to shoot forward with amazing speed.  Those little hooks you see at the end in the top view open and snap shut on the prey.  The mouthpart is then retracted, bringing the food into contact with the other mouthparts so it may be chewed up.  Pretty cool huh?  Granted, it’s hard to really understand how this works unless you see it.  I hope you’ll check out this video to see a dragonfly in action!

Okay, so all odonates have this mouthpart.  This is considered the defining characteristic of odonates in fact.  Nothing else in the world has this style of mouthpart, so if you see it, you know you’re looking at an odonate.  But how do you tell a dragonfly apart from a damselfly?  Let’s take a look at that dragonfly again:

Dragonfly cerci

Dragonfly with rear appendages highlighted

The arrow points to the dragonfly’s rear appendages, which consist of 5 parts (cerci, epiprocts, and paraprocts – big words you don’t really need to know and I only mention for those who like to learn these sorts of things).  Notice how they are pointed in the back?  If you have an odonate with short, spiky rear appendages like this, you’re looking at a dragonfly nymph.  The other way you can tell this is a dragonfly is the shape of the body.  It’s long and slender compared to most bugs, but it’s pretty short and stout as far as odonates go.  So, a dragonfly nymph is an odonate (i.e., it has that funky mouthpart) that is stout bodied and has short, pointed rear appendages.

Now take a look at a damselfly nymph:

Damselfly gills

Damselfly with gills highlighted

Can you see how this is different from the dragonfly above?  Take a look at the part the arrow is pointing to.  Like dragonflies, damselflies have appendages that stick off the back end, but they have 3 instead of 5.  They are also much longer and more flexible than the appendages in dragonflies.  This is because they are gills (more about gills in odonates in a moment) and not just pointy bits sticking off the back end.  Notice also the difference in body shape in the damselfly compared to the dragonfly.  Damselflies are much more slender along the length of their bodies than dragonflies and generally taper toward the end in a way that most dragonflies do not.

So, all odonates have the specialized, extendible mouthpart.  Dragonflies are odonates that have 5 stiff, pointed appendages on the back end and stout bodies.  In contrast, damselflies are odonates that have only 3 appendages (soft, flexible gills) and long, slender bodies.  Easy, right?!  Hopefully now you’ll be able to tell them apart in pictures or if you happen to find and/or see a live one.  There is a lot of variation in size, color, and shape, but dragonflies all share the characteristics described above and damselflies have their own set of characteristics.

I’ll end with a word about gills in odonates.  All odonate nymphs rely on gills to some extent.  The gills are obvious in damselflies, but where are they located in dragonflies?  Dragonflies actually have their gills INSIDE their bodies!  They have a specially modified rectal chamber within their abdomen and the gills line that chamber.  The dragonfly nymphs then pump water into and out of their rectal chamber to aerate their gills and absorb oxygen from the water.  This actually allows dragonflies to do one other cool behavior, but that is a story for another time.

Next time, I’ll discuss the differences between dragonfly and damselfly adults.  Most people probably encounter the adults more often than the nymphs, but few people seem to know the difference even in the adults.  It’s easy, so tune in next time!

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Text and images copyright © 2009 DragonflyWoman.wordpress.com

Metamorphosis!

Before I get into details about more individual insects and groups, I thought it might be a good idea to go over the different types of metamorphosis, or how insects develop.  As you probably know, insects go through several different stages of development and can look very different in each stage.  Let’s look a little deeper into how it works!

Because insects have their skeleton on the outside of their bodies (they have an exoskeleton), they can’t grow the way humans do.  Their skeleton only stretches so far, so if they need to get any bigger, they need a bigger skeleton.  So, they grow a new, bigger skeleton under the smaller one.  This skeleton is soft and flexible so that the whole thing can fit under the hard, outer skeleton.  Then they molt.  When an insect molts, it breaks out of the smaller skeleton and stretches its soft, bigger skeleton out by inhaling a lot of air and pushing fluids around inside it’s body.  When it’s fully expanded, the skeleton hardens (or sclerotizes).  At some point, an insect undergoes a final molt and become an adult.  Once an insect is an adult, it no longer molts.  This means that insects only molt when they are pre-adults, or immatures.

Insects molt several times during development, but the number of molts depends on the insect.  Dragonflies molt many times as they develop, some molting 20 times or more.  Other insects molt only a few times, such as the giant water bugs that undergo 5 molts.

Let’s get back to metamorphosis.  We’ll start with the really simple insects, the ones that don’t have wings.  These include the silverfish and firebrats, though the springtails and some other technically non-insects are sometimes included in this group.  These insects have a type of metamorphosis called ametabolous.  The word ametabolous is Greek and basically means “doesn’t change.”  In most insects,  the immatures look different from the adults to some degree.  In aematbolous insects, all non-egg immature stages look very similar to the adults except that each stage is just a little bigger than the previous one.  This is illustrated in a simple diagram of the life cycle of ametabolous insects:

Ametabolous metamorphosis

Ametabolous metamorphosis

Notice how these insects look alike, just different sizes.  Because the ametabolous insects do not have wings, it can be a little difficult to tell when a silverfish is an adult or an immature.  Only the adults can reproduce though, so if they’re capable of producing offspring, they’re definitely adults.

Other insects undergo incomplete metamorphosis, including the true bugs, grasshoppers and crickets, and dragonflies.  Insects that have this sort of metamorphosis are called hemimetabolous, which is Greek for “partial change.”  In this type of metamorphosis, the immatures look a lot like the adults, except they do not have wings.  Here’s a diagram illustrating this type of metamorphosis:

Incomplete metamorphosis

Hemimetabolous metamorphosis

Can you see the difference between this type of metamorphosis and ametabolous metamorphosis above?  Here, the immatures look a lot like the adult, but there are obvious differences between them.  If you don’t see the difference between the stages in this diagram, focus on the image at the top and the image at the center-right.  Notice how the wings are stretching out past the body in the center-right image and not in the image at the top?  The insect with the full wings is the adult.  All non-egg stages without complete wings are immatures, though many hemimetabolous insects do have wing buds visible.  The immature, non-egg stages of hemimetabolous insects are usually called nymphs.

The last type of insect metamorphosis is the one most people already know, the kind butterflies, flies, beetles, and many other insects use: complete metamorphosis.  These insects are called holometabolous insects, which means “whole change” in Greek.  The immatures of holometabolous insects look very different from the adult stage and are called larvae.  Most larvae are worm-like in shape, hence the “worm” portion of the common names of many insect larvae (e.g. mealworms, glowworms, bloodworms, etc).  Holometabolous insects also have an extra stage in development, the pupa, also commonly known as the cocoon or chrysalis.  When an insect pupates, or turns into a pupa from a larva, it undergoes a complete rearrangement of its tissues so that what emerges looks completely different from what went in.  Here is an illustration of the life cycle of a butterfly, probably the best known of all insect life cycles:

Holometabolous metamorphosis

Holometabolous metamorphosis

The caterpillar on the left lives on and eats plants while the adult butterfly on the right flies around a lot and eats flower nectar.  The pupa at the top is where the transformation from the larva on the left to the butterfly on the right occurs.  Each stage looks and often acts very different from the others.

So there you have it!  All insects undergo some sort of metamorphosis, but which type they use depends on what type of insect they are.  In general, the more primative the insect (or the further back in time it evolved), the less complex its metamorphosis.  The really primative insects, the ones that never even developed wings, use ametabolous metamorphosis and don’t change shape much between stages.  The most advanced insects use holometabolous metamorphosis and drastically change shape between stages.  The rest of the insects fall somewhere in between and use hemimetabolous metamorphosis, a style of metamorphosis intermediate between ametabolous metamorphosis and holometabolous metamorphosis.

I will finish this post with one final note about the words larva and nymph.  There is some debate among entomologists about whether we should call all immature stages larvae to make things more simple (they do, after all, both refer to immature stages in insects) or whether we should continue to call the immatures of hemimetabolous insects nymphs and those of holometabolous insects larvae.  There are many good arguments for and against both sides.  I personally think that we should continue to use both words, nymph and larva.  There is a strong scientific evidence that suggests the equivalent of the larval stage of holometabolous insects occurs within the egg in hemimetabolous insects.  Hemimetabolous insects have nymphs and not larvae because their “larval stage” is complete before they hatch.  There is also evidence that suggests that the pupa of holometabolous insects is equivalent to all of the nymphal stages of hemimetabolous insects combined.  The holometabolous insects  don’t have nymphs because their “nymphal stage” occurs within the pupa.  (For any scientists out there who might be interested in learning more about this, please see the excellent 1999 Truman and Riddiford article “The Origins of Metamorphosis” in Nature Vol 401, pp 447-452.)  There is thus a valid scientific reason for continuing to use both words.  I also like to use both because whoever I’m talking to about an insect immediately knows what type of metamorphosis it uses (and whether it’s primative, intermediate, or advanced) based simply on the word nymph or larva.  Although it’s slightly more difficult to learn two words originally, they are easier to use in the long run because they convey so much information in two short, simple words.

All this to present background information for my next few posts!  Next time, I’ll discuss a group of hemimetabolous insects that have many nymphal instars (or stages between molts in the immature stage) and some of my favorite insects: the dragonflies and damselflies.

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Text and images copyright © 2009 DragonflyWoman.wordpress.com

Musings on moldy bugs

Last fall, my swamp cooler acted up and everything in my apartment ended up getting moldy.  I found mold on a hat that was packed away in a closet, growing on my interior doors and cabinets, on a piece of jewelry made with natural materials, books, and sundry other objects.  Much to my horror, I also found a box of bugs in my collection had gotten moldy.  There are several things you don’t want to see when you look at your insect collection.  Damaged specimens that have been handled improperly or dropped (especially by someone else who didn’t tell you they did it) are always bad.  Carpet beetles get into your collection and eat all of your bugs.  That’s right – some bugs eat dead bugs!  Carpet beetles are the scourge of most entomological collections and can decimate an otherwise perfect collection in a very short period of time.  Most insect collectors use mothballs or cyanide-based chemicals to protect their collections from carpet beetles.

Mold isn’t something you want to see in your collection either.  I recently got around to attempting to clean off the moldy bugs in an effort to save them and, oddly enough, I learned some very interesting things in the process.  There seemed to be a nifty connection between the habits of a particular bug and the amount of mold that grew on it.  For example, this bug is a carrion beetle:

carrion beetle

Carrion beetle

I pulled it off a dead snake I found out in the field several years ago.  (Dead animals are an excellent source of insects!)  Carrion beetles are decomposers and eat dead, rotting things.  Needless to say, this insect was wallowing around in nasty things when it was alive, all kinds of bacteria and molds that were helping break the snake down as it rotted.  When I cleaned the mold from my insect collection, the carrion beetle was completely covered, as in 1/4 of an inch thick across it’s back!  I couldn’t even tell it WAS a carrion beetle until I cleaned it off.  When I thought about it later, it made sense to me that it would be one of the bugs with the most mold.  It lived in rotting animals and likely picked up some mold spores while it was eating its dinner.

Among the less moldy bugs was this wasp:

velvet ant

Velvet ant, a type of wasp

It makes sense that this bug didn’t have much mold on it if you know something about it.  In this photo is a wasp called a velvet ant.  This particular type of wasp is a parasite that stings other insects to paralyze them and then lays its eggs inside the still living body of its victim.  The larval wasps eat the insect as they develop.  The adult eats nectar.  This wasp isn’t crawling around inside the rotting remains of a dead animal and likely barely touches things that have a lot of bacteria and molds growing on them.  It makes sense, then, that this insect wouldn’t have as much mold living on it when I put it in my collection compared to the carrion beetle that was living in a soup of mold spores and bacteria.

Another bug with very little mold was this giant water bug:

Lethocerus medius

Giant water bug

It’s typical to dispatch aquatic insects in alcohol, so this guy was soaked in an antiseptic liquid for a time before it was pinned.  It makes sense that this insect wouldn’t have much mold on it’s body for this reason and indeed it had less mold on its body than any of the other insects.  Based on the amount of mold on this insect compared to the others in the box, I came up with a plan for how to clean them: alcohol.

So, I cleaned all of the insects in the box of moldy insects one by one with a paintbrush dipped in alcohol to counteract the mold build-up.  It worked for now, but we’ll see if it comes back this summer.  But for now my collection is looking pretty good once again.  This is what you want to see when you have a collection:

My collection

One unsorted box of my insect collection

A nice clean box of insects, free of live bugs and mold!

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