Stereotypical Ladybug Behavior (Well-Nigh Wordless Wednesday)

You always hear about ladybugs eating aphids, but I’ll be honest: I’ve watched thousands of ladybugs, and I’ve never actually seen one eat an aphid.  Until, that is, I got this photo of a seven-spotted ladybug eating an oleander aphid on common milkweed recently:

Ladybug eating an aphid

Woo!  A ladybug doing what everyone always talks about them doing!  It was an exciting moment for me for some reason.  :)

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth.

Fly on Fly Noshing (Well-Nigh Wordless Wednesday)

Last week, I was helping an employee measure leaves for a project she’s doing for her master’s degree when she came across this awesome robber fly:

Robber fly on bid leaf magnolia

Robber fly on bid leaf magnolia

Watching robber flies always feels kinda like watching one of those nature documentaries to me, the kind where a cheetah is chasing a gazelle.  You feel sorry for the gazelle when the cheetah gets it, but you are also secretly just a little happy to see the cheetah take it down.  Robber flies are the cheetahs in this scenario and the little midge it’s got is the gazelle.  You can’t help but root for the robber fly a bit, even though it’s sitting there sucking out the brains of another insect.

Isn’t nature gloriously gruesome sometimes?

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth

Well-Nigh Wordless Wednesday: Sluuuuuurp!

I was out with my intern a few weeks ago looking for caterpillars and showed her some spicebush swallowtail and black swallowtail caterpillars before we made our way to the pipevine to look for pipevine swallowtail caterpillars. She hadn’t ever seen the pipevines, so I pointed out a few and we started looking around to see how many we could find on the plants.  I peered into the leaves trying to find a big caterpillar that was about to pupate when I saw a really odd-looking, shriveled caterpillar.  I assumed it was dead, but when I looked a little closer it moved.  So I looked even closer and saw this:

Jumping spider eating a pipevine swallowtail caterpillar

If that spider could smile, it totally would!  He (or she) looked quite pleased with himself and was dragging the wrinkly carcass around with him as he tried to hide under a leaf.  He was NOT letting that thing go – it was probably the score of a lifetime!

Isn’t nature grand?

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth

Dragonfly Swarms: Static Feeding Swarms

At long last, I am finally getting to the information about static swarms in dragonflies!  Apparently posting once a week is a bit ambitious for my current schedule and even my weekend became one giant black hole of work.  I’ve had no time to blog!  Better cram this post in quick while I have a few free minutes…  :)

Before I jump into what’s known to science about static dragonfly swarms, take a moment to ponder the amazing swarm depicted in this image I found online:

Isn’t that glorious?!  I can’t be sure that this is a real photo, but based on what others have reported and what I’ve observed myself, this is certainly not outside the realm of possibilities!  The people in the photo aren’t enjoying the experience, even though the dragonflies in the swarm were completely harmless.  I wish I were in their place!  I would run out and stand in the middle of the swarm, soaking up the sound of the dragonfly wings fluttering against one another and the sight of several thousands of my favorite animals flying in a single location.  This is what my heaven looks like!  (And yes, you read that right: I did just say that my heaven involved massive numbers of flying insects.  What can I say?  I’m an entomologist!)

Now for the science!  If you’ve read any of my swarming series, you know that dragonflies migrate, sometimes in mass migratory swarms, and that migrating dragonflies have patterns of behavior similar to migrating birds.  I have also speculated, based on my own observations and those of people who reported swarms to me early this summer, that the non-migratory swarms (what I call static swarms) are feeding swarms.  Today, I’m going to go over what’s known about these swarms.  Unfortunately, most of this information is either buried in the scientific literature where it’s largely inaccessible to the public or in a $100 dragonfly book that, while truly brilliant, is also largely inaccessible.  And let’s face it.  Apart from college libraries, only odonatologists (scientists who study dragonflies) and other entomologists are going to shell out that kind of cash for a dragonfly book.  For those of you who don’t LOVE DRAGONFLIES SO MUCH that you’re willing to run out and fork over 100 bucks for a book (i.e. you’re normal), I’ll summarize what is known about static swarms here!

First of all, the static swarms are almost always feeding swarms!  I’ll go over the reasons why you might see these feeding swarms in a particular area in a moment, but first a few interesting facts.  First, this behavior appears to be exclusively anisopteran.  This means that the behavior is observed in dragonflies only, not their close relatives the damselflies.  This is probably because dragonflies exhibit vastly superior flight compared to damselflies. However, among dragonflies, many species of both perchers and fliers will take part in the swarms and fly for extended periods of time.  Both males and females swarm, though males are more commonly observed.  Swarms can be made up of several different species, and can even include other organisms, such as the vertebrate birds and bats.  If birds or bats are present, they will usually be found just above the dragonflies, feeding on the same insects the dragonflies are eating rather than on the dragonflies themselves.  And for those of you who are shocked at the number of dragonflies in the swarms you’ve see, you likely only saw the tip of the iceberg!  In one of the only studies looking at the number of individuals swarming within a population, only 16% of the dragonflies in the area participated in the swarm.   Just think: if you see 1000 dragonflies in a static swarm, that means that there were likely 6250 total dragonflies nearby!

You’ll most often see dragonfly swarms near dusk or dawn, and it’s thought that the dragonflies can see flying prey (most often mosquitoes or non-biting midges, but also termites, ants, and honey bees)  better when the sun is close to the horizon.  During these times, you may notices that dragonflies appear very suddenly, fly in circular patterns over a very specific area for some time, and then disappear as quickly as they arrived.  This is because the dragonflies are attracted to large groups of prey organisms.  Once the prey numbers drop or they become less active (e.g. as it get darker), the dragonflies move on.  If the prey return the next day, the dragonflies likely will too.  In some particularly productive areas where prey are consistently available, you might even see a swarm form nearly every day for months.

There are several reasons why dragonflies might congregate in one area versus a similar area nearby, but in nearly every case there is an abundance of prey species present in the area containing the swarm.  Dragonfly swarms will form where other insects are swarming.  Most people have seen a big swarm of gnats at one point.  Those swarms are like a dragonfly buffet!  The dragonflies will swoop in and out of the fly swarm, picking off flies and eating them on the wing before going back for more.  This is likely what happened in August when the dragonflies descended on Milwaukee.  Massive numbers of mosquitoes in the area drew dragonflies into the city and large swarms formed where the mosquitoes were congregating.  Dragonfly swarms often form when there is a seasonal emergence of ants or termites as well.  This was the case in the swarm I witnessed.  The ants and termites were emerging out of the grass and the dragonflies were catching and eating them as they emerged.

Dragonflies might also be attracted to objects that attract other insects.  If prey insects are consistently attracted to a particular object, dragonflies can learn to associate that object with a good meal.  In one study, dragonflies were found over a set of traps intended to attract other insects, feasting on the insects flying in toward the trap.  The prey insects eventually stopped coming to the traps, but the dragonflies returned for several more days.  In this case, the dragonflies were attracted to the traps and not the insects themselves because they’d learned to associated the traps with an abundance of prey.

Dragonflies might also be observed swarming in areas where a weather front has just passed through.  Insects often get trapped in fronts and are pushed along with the winds for some time before being deposited somewhere else.  When they finally free themselves from the front, they might find the dragonflies ready!  Dragonflies take advantage of these windfalls of prey by forming swarms and eating the insects as they arrive.  This sort of feeding also happens during migratory flights.  The same fronts that deposit large numbers of prey insects in an area help the dragonflies fly long distances, so prey is readily available when the dragonflies stop to rest and feed.

In wooded areas, many insects will congregate in sunny, open patches.  Lots of dragonfly swarms form in small sunny patches to take advantage of the other insects that are attracted to the spaces.  The swarms of prey insects will move as the sun changes position, os the dragonflies will move too.

In high winds, insects will congregate in lee areas (areas protected from the wind).  Lees promote dragonfly swarming behavior because of the high abundance of insects found in these areas.

Finally, and I think most remarkably, some dragonflies will swarm in areas where insects are being stirred up due to some sort of disturbance.  Mowing your lawn?  It disturbs the small insects living in your grass and cause them to fly around more than they usually would.  The prey draws the dragonflies in and swarms form.  Similarly, some dragonflies have learned to follow large, slow moving objects (these could be people, bicycles, cows, cars, etc) because they disturb prey insects as they move and encourage the prey to fly – often into the eager grip of a hungry dragonfly.

So all of this boils down to one simple concept: any time you have an abundance of dragonflies in an area as well as a significant prey population, you are likely to see dragonfly swarms.  The behavior is thus fairly common in many different species of dragonflies.  That said, the chances of a single person seeing more than one or two swarms in their lifetime in a single area can be quite low.  The conditions have to be just right for swarms to occur, perfect for both a large number of prey insects AND a large number of dragonflies to exist in the same area at the same time.

Next time (and I’ll get the post up much more quickly this time), I’m going to discuss some of the references available for identifying dragonflies, both in print and online.  In the meantime, keep sending me swarm reports!  I am beyond thrilled with the participation in my swarm project, so keep ’em coming!

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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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Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.wordpress.com

Giant Water Bugs Eating

I didn’t post anything last week because I was in the midst of chaos with family and friends, making final preparations for my wedding last weekend.  But now I’m back at the computer and getting things done!  Since I just took a short break, I thought I’d take this opportunity to express my thanks to everyone who’s been keeping up with my blog.  I appreciate your comments and your support!  It’s gratifying to know that something I enjoy doing so much is informative and helpful to others.

Lethocerus indicus eating a small fish

Lethocerus indicus eating a small fish

Today I thought I’d post a short video that illustrates how giant water bugs eat.  Giant water bugs are fierce predators and are known for being able to take down very large prey such as snakes, fish, turtles, and even birds!  Even more amazing is that they accomplish these feats while they barely move at all!  Giant water bugs are called sit and wait predators.  If you think about that phrase for a moment, the behavior it describes should become obvious: giant water bugs sit in one place and wait for prey to swim by.  As much as I love giant water bugs and try to get people excited about them, I’m the first to admit that they sit in one place for long periods of time without moving at all.  In fact, they can even be a bit boring to watch at times.

Abedus herberti

A giant water bug in the pose they normally adopt while waiting for food to swim by.

However, any boredom instantly disappears if the giant water bug you’re watching encounters food!  Part of what makes them exciting to watch is their structure.  I wrote about how to tell the American giant water bug genera apart several months ago and talked about the raptorial forelegs that giant water bugs possess.  Most of the time, you’ll see giant water bugs sitting underwater, holding onto a rock, the bottom of the pond or stream, or a piece of vegetation with only their hind two pairs of legs.  The front legs, those strong raptorial forelegs, are held in front of them, as in the photo above.  If food swims by, they thrust those muscular forelegs forward very rapidly, fold the legs over the food, and then retract their legs back toward their bodies, bringing the prey close to their heads.

The giant water bug then begins to eat its food.  First, it has to find a place it can insert its piercing-sucking mouthparts, that beak that you can see hanging off the front of the head of the bug in the image above.  It will probe the prey item with its beak until it finds a soft place into which it can insert its mouthparts.  The water bug then injects the prey with chemicals that break the tissues down, turning them into a sort of soup.  Finally, the bug sucks the liquid out of the prey and into its own body.  This part is rather like what you do when you take a drink or eat a smoothie with a straw!

Depending on the size of the prey item, the eating part of the process can take a very long time, up to 10-12 hours.  It takes a long time to inject all those chemicals and suck up the resulting soup.  But the prey grabbing happens VERY fast!  So fast that most prey items probably don’t even see the bug before it’s too late.  And so fast that the very first time I fed a bug as a graduate student, I dropped the forceps in which I held the prey (a mealworm) and jerked my hand out of the way as hard as I could.  There may or may not have also been a loud girlie shriek involved, one that I may or may not have been very happy that no one else was in the lab at the time to witness.  :)

So, to get an idea of just how fast water bugs are when they grab food, I recorded my lab bugs the last time I fed them.  Without further ado, I give you a giant water bug (species: Abedus herberti) eating a mealworm!  Pay special attention to how fast the bug grabs the mealworm.  If you look closely, you can also see it probing the mealworm with its beak!  Look for the probing in the space between its eyes and its left foreleg:

Pretty cool eh?  That speed and power in their forelegs allow giant water bugs to catch and eat some very large things.  How amazing is it that an insect, and an aquatic insect at that, can capture and consume a bird?!  And I’m not talking about little birds either.  There is a published report of one taking down a woodpecker.  Now that’s just impressive.

I should be back to my usual posting schedule now, so look for a new post next week!  I’ll be installing an educational aquatic insect pond at the Biosphere II soon, so I’ll be posting about that for sure.  But first, another quick video, this time of a non-insect aquatic invertebrate: the flatworm!

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Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.wordpress.com