Sexing Giant Water Bugs

Female giant water bug

Female giant water bug

I am asked how to tell male and female giant water bugs apart more often than I would have ever imagined.  It would seem that there are a limited number of people in the world who can sex water bugs, so I have a rather steady stream of people asking me how to do it.  A few weeks ago I started looking around online to see if there was any information about sexing water bugs, but there’s really nothing available.  Well, there’s one article that is absolutely and completely wrong (I’m not even going to link to it, but don’t listen to anything the person who wrote the eHow article on the subject says!), so that’s no help at all.  It’s high time that this information be made available online!

Sexing belostomatids (aka, giant water bugs) isn’t always trivial.  The males and the females have the same coloration, so you can’t use color differences.  The females are often a little bigger than the males, but there’s a lot of variation in size in both sexes and it can be difficult to tell whether an individual is “big” or “small” unless you have many other individuals to compare with it.  You can sometimes use behaviors to distinguish sexes, especially during the mating season.  For example, if a bug is carrying eggs on its back or climbing up a stick to tend to eggs, it’s a male.  But… you also can’t be sure you have a female just because one doesn’t have eggs, even during the peak of the mating season.  Instead, you need to rely on a structure that varies reliably between the sexes.

Giant water bugs DO bite, but you’re going to have to hold them in place if you want to tell which sex you’ve got.  That usually involves picking them up, so if you do choose to sex water bugs yourself, be careful!  When I pick up water bugs, I use my middle finger and my thumb and press the bug down onto the bottom of whatever habitat/container they’re in.  I then grasp water bugs by the sides of the thorax, as it’s a very rigid part of the body where you can get a firm grip, and use my index finger to support the bug (I apologize that I only have a grainy black and white photo of this…):

Holding giant water bugs

Holding giant water bugs

You need to hold on tight, especially with the larger species, because they are surprisingly strong and will try to wiggle free.  Once you get a good hold on one, you’ll need to flip it over.  The part you need to look for is on the bottom of the abdomen:

Genital plate

Genital plate

This structure is called the genital plate, and it conceals the reproductive organs underneath.  Don’t worry!  You don’t need to go digging around to find internal parts and can use the shape of the genital plate itself.  The shape of the plate varies from genus to genus, but there are some general rules.  The genital plates of male water bugs are smoothly rounded at the tip (the part closest to the back of the bug) and complete (i.e., have no splits or gaps).  For example, the genital plate of males in the genus Abedus look like this:

Abedus male genital plate

Abedus male genital plate

The arrow points to the continuous and smoothly rounded tip of the genital plate.  Here’s a drawing in case the shape is difficult to see in the photo:

Abedus male genital plate

Abedus male genital plate

See?  Rounded at the tip, no splits or gaps.  The females are different.  In some water bug genera, there are splits, notches, or gaps at the tip of the genital plate, so that the line around the tip of the plate is broken.  Many of them have flattened areas at the tip of the genital plate so that they are not completely round.  Most have two distinct little tufts of hairs, either at the edges of a notch at the tip of the genital plate or alongside the midline of the genital plate near the tip.  For example, here’s a female Abedus:

Abedus female genital plate

Abedus female genital plate

In this image, the arrow pointing up from the bottom indicates the flattened, slightly notched part of the genital plate while the arrow coming from the side points to the tuft of hair on the right side of the midline.  The drawing:

Abedus female genital plate

Abedus female genital plate

The little tufts of hair can be quite small and the shape of the genital plate only subtly different from the male, but there are definitely two little tufts of hair on either side of the midline, a flattened area at the tip, and a small split at the tip of the genital plate in Abedus females.

These structures can vary in appearance from species to species, and especially between genera.  For example, this is the genital plate of a male Lethocerus:

Lethocerus male genital plate

Lethocerus male genital plate

Even though it’s much longer and narrower than Abedus, the arrow indicates the same sort of rounded, unbroken tip of the genital plate.  There is a fringe of hair along the tip of the plate in this species, but note that there are no distinct tufts of hairs anywhere.  There’s a groove that runs the length of the middle of the plate, but it doesn’t leave a gap at the tip.  In contrast, here’s the female:

Lethocerus female genital plate

Lethocerus female genital plate

The arrow here points to the tuft of hair to the right of the midline.  In this species, the tufts are at the very tip of the genital plate rather than on the upper surface and recessed from the edge as in Abedus.  There is also a small notch between the two tufts, though it’s a little difficult to see in the photo.

And that’s it!  Smooth, round genital plates in males and flatter, sometimes broken genital plates with two tufts of hairs in females.  In the US, the genital plates of the genus Belostoma are very similar to those shown here for Abedus and other American Lethocerus are similar to the Lethcerus pictured here, so the images here will help with sexing US water bugs.  Other genera in other countries follow similar patterns, but may have some slight differences.

Good luck!

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

Friday 5: 5 Water Bugs

As part of my Ph.D., I’ve had an opportunity to work with the eggs of several different giant water bug species.  I’ll talk about my studies and what I’ve learned here eventually, but one of the things I like most about my research has been working with live water bugs from all over the world.  It’s a really great perk if you’re a bug geek like me!  Today I’m going to highlight 5 species I’ve had living in my office or lab at one point and share a few facts about them.

Abedus herberti

Abedus herberti

Abedus herberti

You’ve all seen this one before!  This is the giant water bug I work with most, the back brooder that is native to Arizona.  This bug is a fairly good size (usually an inch or more) and has an elegant oval shape that I find oddly pleasing.  I think they’re the cutest of the giant water bugs (my completely subjective personal opinion!), but they’re also a lot less aggressive than most of the other bugs I’ve worked with.  In fact, they’re rather laid back for water bugs!  They’re still a lot of fun to watch though.  Granted, they tend to sit very still in one place for long periods of time, but they have some fascinating behaviors that I’ll talk about in future posts.

Lethocerus medius

Lethocerus medius

Lethocerus medius

This is another Arizona native, and one you’ve seen here before.  This is the biggest species in Arizona, but actually one of the smallest Lethocerus species overall.  Not that 2+ inches makes for a small bug, but giant water bugs get much bigger than these!  Medius is a lot of fun to work with, but they’re very different from their Abedus cousins.  They’re aggressive, willing to eat anything they can get their claws on, and live in some really disgusting habitats.  They’re also emergent brooders and will fight anything that tries to mess with their eggs.  I like their feisty personality, though I’ll admit that sometimes they startle me when I feed them.  They are rather vigorous when it comes to capturing food and I can say from personal experience that it’s a little disturbing to see a 2 inch long predatory bug climbing up the tweezers toward your hand!

Lethocerus indicus

Lethocerus indicus

Lethocerus indicus

This is another emergent brooding Lethocerus, but indicus is a lot bigger than medius!  I’ve only had one live one, but I kept her in a tank on my desk for over a year and enjoyed watching her. She was from Vietnam and made for an excellent conversation piece because she was so enormous.  She would also get into these epic battles with the goldfish I fed her, splashing water all over my desk as she wrestled with her soon-to-be dinner.  I was really sad when she died, but I’m practical too.  Nothing illustrates the giantness of giant water bugs like pulling out my nearly 4 inch long specimen at an outreach event  and saying that giant water bugs get even bigger.  I wish I could photograph the facial expressions people make upon hearing this news!  Many are shocked, really and truly shocked, to learn that there are insects that big living in water.  Come to think of it, I should cue up some Jaws music next time I pull my indicus out…  Okay, that would be mean and just make people more scared of water bugs than they already are, which is completely against the point of outreach.  Maybe I should stick to some nice, quiet Grieg instead, perhaps “Morning” from Peer Gynt.  :)

Diplonychus rusticus

Diplonychus rusticus

Diplonychus rusticus

This is another Vietnamese back brooding bug, but this is a genus that we don’t have in the New World.  I was so excited to have these!  They are odd-looking little water bugs with strangely shaped heads, but their air straps, the little protrusions on the back-end that they use to collect air at the surface, are so beautiful!  See those little fluffy bits sticking off either side of the back-end?  Those are the air straps and they expand out into these gorgeous feathery things when fully extended.  I spent hours watching their respiratory behaviors and filmed many more hours of it.  I might revisit the data sometime after I’m done with my degree and have more time to look over my videos again.  For now, I settle for looking through my rather terrible photos now and again and remembering how fun it was to have such a great bug in the lab.

Belstoma micantulum

Belostoma micantulum

Belostoma micantulum

Belostoma micantulum is not a giant giant water bug.  In fact, it’s one of the smallest species of giant water bug, topping out at about 3/8 inch.  They’re surprisingly agile and aggressive little bugs though, and, as you can see in the photo, are willing to capture and eat animals that are relatively quite large.  They also have eggs that are big for their bodies that they drag around with them on their backs, one of the reasons that I included them in one of my studies.  These little guys came from Argentina and lived only a short while, but it was fun to watch such tiny and fiery little bugs swimming around their bowls like they owned the place.

Ah, water bugs!  I just love them!  And getting to work with species from other counties is really exciting.  Not quite as exciting as it might be to, say, travel to the bugs in their native lands, but pretty darned thrilling for someone who spends a lot of time in a lab like I do.  And look out for another water bug post soon!  I just had a paper accepted, so I feel like I can actually share one of my favorite studies with you all now, maybe in a few weeks.

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

The Long, Involved Process of Giant Water Bug Mating

For my dissertation, I am researching how giant water bug eggs benefit from the care provided by their fathers.  It’s a really interesting subject and I’ve learned many exciting things.  You’ll hear more about my work in the future.  You can’t just study the eggs of giant water bugs though because they are intricately linked with the adult males.  To do my work, I have to know a lot about brooding behaviors so that I understand how the eggs in different groups respond to the particular care they receive.  To get eggs to work with in the first place, I also have to know a lot about giant water bug mating practices and preferences.  For example, I have learned that it is nigh impossible to convince giant water bugs in the genus Lethocerus to lay eggs in the lab.  Sure, you can do it and some people have successfully, but my lab doesn’t provide the right conditions.  Thus, I have to collect mine in the field.  The genus Abedus is much more cooperative.  Put a gravid female (a female full of eggs, ready to be fertilized and laid on the back of her mate) and a male in a little bowl of water with a rock and the next morning you usually have 30-100 eggs that you simply scrape off the back of dad.  Easy!

The process by which those eggs are fertilized and deposited by the female onto her mate’s back is anything but easy though.  Water bug mating is a very long, involved process in the back brooders, but there’s a good reason for it.  Ponder this for a moment: you’re a giant water bug male and you’ve just found the water bug woman of your dreams!  You want to be her baby daddy, but children tie you down.  They’re expensive too: while you carry her eggs around with you, you won’t be able to fly, are more vulnerable to predators, will have a harder time swimming, etc – huge costs if you’re a studly male giant water bug!  Plus, you suspect that your new lady love may have been a bit promiscuous in the past…  If you’re going to be a water bug daddy and raise your gal’s expensive kids, you want to be darned sure that those kids are yours before you commit.  Luckily, giant water bug mating practices ensure just that.  Let’s go over how it works, shall we?

The most important step of all comes first: finding a mate.  If you can’t find a member of the opposite sex, having kids is pretty much out of the question.  The back brooders I work with the most, Abedus herberti, exhibit a very interesting behavior to attract mates: they do frantic push ups:

As you can see, the push ups create little waves in the water.  And, if you know anything about how ear drums work, you have a pretty good idea of what these little waves do: the male water bugs are calling out to potential mates by creating waves in the water that are perceived as sound by the females.  It’s the water bug equivalent of a pickup line!  If the female wants to mate, she’ll track the male down and indicate that she’s willing to mate.

Once the pair gets together, they stay in near constant contact until they’re finished mating.  The bugs will climb all over each other and rub each other with their legs.  But first things first!  They mate:

giant water bugs mating

Giant water bugs mating (Abedus herberti)

This usually takes several minutes and involves the usual parts coming into contact with one another and the transfer of sperm from the male (red dot) to the female (white dot).  When they’re done mating, the female will try to climb onto the male’s back to lay eggs.  However, I’ve never seen a male that will allow his mate to lay eggs after mating only once.  No, they have to mate again!  And probably again.  And maybe once (or thrice!) more, for good measure.  If the male isn’t ready for his lady to lay her eggs, he’ll move around so she can’t lay and do more push ups to indicate that he wants to mate again:

As you can see in the video, there’s a bit of a struggle: the female wants to lay her eggs, so she’s persistent.  But the male’s also determined to mate again, so he keeps thwarting her attempts.  Eventually, however, the male will have mated enough and will allow the female to climb on his back to lay eggs:

Abedus herberti mating

Abedus herberti laying eggs. Female at top, male at bottom.

So, the bugs mate several to many times and the female lays her eggs.  They’re done, right?  Wrong!  The males generally only allow the females to lay 1-4 eggs at a time.  After that, he shakes her off his back and insists that they mate again.  Then she lays a few more eggs.  Then they mate again.  Then they rinse and repeat, oh, 10-50 more times.  The male eventually looks something like this:

water bug dad with eggs

Water bug dad with eggs

The whole process can take several hours!  As I said, it’s a very involved behavior.  Then the female swims away and leaves dad to take care of the kids until they hatch.

Let’s think back to those expensive kids for a moment.  Females are essentially big bags of eggs and do not care for their young at all.  It is in their best interest to mate once, lay as many eggs as possible as quickly as possible, and be on their way.  But the males will drag their needy children around for 1-3 weeks.  If they’re going to bear the costs of parenthood, they want to be sure that the kids they’re lugging on their backs are actually theirs.  The mating system that I described helps them do just that!  Suppose a female has mated before.  Many insects can store sperm so that sperm from multiple males mix together as the eggs are fertilized and laid (or oviposited if you want to use the technical entomological term).  For male water bugs, this isn’t the ideal situation.  To help ensure that all the eggs on their backs are their own offspring, they insist on mating 10, 15, 20, 30, 50 times.  In doing so, a male flood the female’s reproductive tract with his sperm, making it highly unlikely that any of the eggs on his back belong to other males.  It’s a complicated mating system, but it is an important one, at least for the male.  This way, he’s sure that he’s not wasting energy and resources caring for another man’s kids and is instead devoting himself entirely to his own children.

This is just one of the many interesting behaviors that giant water bugs exhibit!  I think my bugs are absolutely fascinating, so look for most posts about them in the future.  :)

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

Friday 5: Fun Facts About Giant Water Bugs

This week’s Friday 5 features a subject near and dear to my heart: giant water bugs!  If you aren’t familiar with these beasts, they have some really amazing characteristics that make them a fascinating group of insects to study.  I’ve already covered giant water bug parental care and feeding in other posts.  Today I’m going to share 5 fun facts about giant water bugs.  I hope that knowing these facts will help you fall in love with these wonderful bugs!

Lethocerus medius

Lethocerus medius, the biggest giant water bug in Arizona, can reach lengths of nearly 2.5 inches!

1.  The largest true bug (i.e. member of the insect order Hemiptera) in the world is a giant water bug.

Lethocerus maximus is truly a giant, reaching nearly 5 inches in length!  However, if you want to add one to your collection, you’ll have to visit northern South America.  The Lethocerus in the US are piddly in comparison, topping out at about 2.5 inches – half the size of the biggest species.

Abedus cannibalizing eggs

A male Abedus herberti cannibalizing his own offspring after he scraped them off his back.

2.  Giant water bugs can be cannibalistic.

A hungry giant water bug will eat almost anything it can get its claws on, including its own young (only when very hungry or something has gone wrong with the eggs a male is caring for), the young of other individuals, and each other.  Female Lethocerus are also known to rip apart the egg clutches deposited by other females when there aren’t enough males with good egg laying sites to go round.  However, I haven’t observed giant water bugs eating each other in the field unless there is very little other food available and they are getting desperate.  It would seem they prefer not to eat each other, but they will when they have no other choice.

Abedus herberti mating

Abedus herberti mating.

3.  Giant water bug mating can take several hours, especially in the back brooding species.

Mating is a long, involved process in the back brooding giant water bugs.  First the male does little push ups in the water.  These are thought to send vibrations through the water that the females respond to.  After a male and a female find one another, they mate.  Then the female climbs on the back of the male and lays a few eggs, maybe 4.  Then the male shakes her off and they mate again.  Then she lays a few more eggs before being shaken off again.  This goes on and on until most of the back of the male is covered with eggs, sometimes 150 altogether!  You can see how this might take a long time.  The water bugs in the photo took over 6 hours to lay all of their eggs.

Belostoma micantulum

Belostoma micantulum, a giant water bug from Argentina, is one of the smallest giant water bugs in the world.

4.  Not all giant water bugs are giant.

Belostoma parvum, a giant water bug from northern South America, can be less than a centimeter long.  It’s a not-so-giant water bug!  In fact, several species of giant water bugs in the genus Belostoma are actually quite small and don’t live up to the “giant” in their name at all.  The giant water bug pictured here is Belsotoma micantulum, a tiny little giant water bug that maxes out at a little over a half an inch long.  Pretty cute though, especially when munching on a mealworm that is WAY too big for her!  :)

flood

The only flash flood I've ever personally witnessed, though it's hard to see how big this flood was in this photo! Clicking on the photo will take you to a cruddy, low-res video I shot of it and posted on YouTube.

5.  At least one species has a nifty flood-avoidance behavior.  

Imagine you’re an aquatic insect and a flash flood is headed your way.  You’re going to be ground into a bloody pulp if you stick around.  What do you do?  If you’re the giant water bug Abedus herberti, you climb out of the stream before it floods!  This species crawls out of the water and walks perpendicularly to the bank until it reaches shelter away from the stream.  After the flood passes through, it crawls back into the water and carries on with its regular activities.  Awesome behavior!  And you can see a video of it online by visiting Dr. Dave Lytle’s website.  He filmed Abedus herberti leaving the stream after artificially simulating flood conditions with a fire hose.  The video is hilarious, so I encourage you to take 30 seconds out of your day to watch it.

Aren’t giant water bugs cool?  I love my bugs.  Considering they mostly just sit in one place hoping that food will swim by, it never ceases to amaze me just how many wild characteristics these bugs really have.  Hope you enjoyed this little peek into some of the many fascinating things these bugs have going for them!

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

The Anatomy of Insect Eggs

I work with giant water bugs in my research, but the main focus of my work is actually their eggs.  All the behaviors I observe and the physiology I measure are related to the egg stage of their development.  Today I thought I’d give a crash course in insect egg anatomy using my giant water bugs as models.

But first, a quick disclaimer!  Giant water bugs have strange eggs.  The insect developing inside the eggs require parental care and cannot survive without it in the wild (you can get them to hatch without the parents under certain laboratory conditions) and the exact locations of the structures on the eggs you’ll see here are different from many other insect species.  Still, giant water bugs have the same structures as other insect eggs and those structures do the same things for the insect developing inside the egg as they do in other species.  Just remember that parental care of eggs is rather rare in insects, and the paternal parental care of the giant water bugs barely exists outside their group.

Okay, first things first!  Let’s start with a cluster of eggs:

Abedus herberti

Abedus herberti

Some insects lay their eggs in clusters and others will lay them one by one and really spread them out.  Water bugs lay in clusters so you can see the cluster of eggs where it has been laid: on this male Abedus herberti’s back.

If we zoom in a bit closer, we can start to see what the eggs look like:

Abedus eggs

Abedus herberti eggs, up close!

Abedus herberti eggs happen to change in structure about halfway down, so that’s why you can see the brown change to grey in the photo above.  Some insects do this, others do not.  Regardless, the shell of insect eggs has a special name: the chorion.  Let’s zoom in a bit more and get a good close look at the chorion on the top of the egg:

Abedus egg top

Abedus herberti egg top

This image was taken using a scanning electron microscope (SEM) so that you can get a VERY close look at the structure of the chorion!  This egg was mounted onto an SEM stub upright so that you are looking down at the top of the egg here.  Notice the area indicated by the arrow.  That area is called the micropylar region.  If you look very closely at the image (you can click on it to make it bigger), you can see little white marks within the micropylar area.  Those lines represent the micropyles:

micropyles

The micropyles

Eggshells are meant to contain the animal growing inside them and protect them from the environment.  If anything needs to get into or out of an egg, it has to go through the shell.  That’s where the micropyles come in!  Female insects produce the eggs, but the chorion is deposited before the eggs are fertilized.  Sperm have to get inside the eggs to fertilize them and have to go through the shell to do so.  They enter through the micropyles to pass through the chorion to the egg waiting inside.  The arrow in the photo above shows one micropyle within the micropylar region of Abedus herberti.  There is a second micropyle to the left.  This species has anywhere from 2 to 7 micropyles arranged in an arc, but other insects have different numbers and arrangements of micropyles.

Let’s zoom back out a bit and take a look at the structure of the top of the egg again:

Abedus egg top,showing aeropyles

Abedus herberti egg top

In this image you can see the fine structure of the chorion and see all the little polygons that cover the surface of the egg.  Many insect eggs exhibit raised polygons similar to the ones you see in the Abedus herberti egg.  These are an artifact of the chorion production process in females.  I’m not going into it now because the process by which insects produce eggs is long and involved and better suited to a series of posts (I wrote 19 single spaced pages on this subject as part of the written part of my Ph.D. comprehensive exams!), but those polygons represent the shape of cells that are involved in building the chorion and they’re visible on many insect eggs.

The embryos developing inside the egg need oxygen to survive, but they have to get it from the atmosphere outside the eggshell.  That means the oxygen has to cross the eggshell before the embryos can make use of it.  Sperm enters the egg through micropyles.  Oxygen enters through aeropyles.  The arrow in the image above points to an aeropyle on the chorion of Abedus herberti and you can see several of them dotting the surface of the egg.  I think they look rather like lunar craters!  Let’s take a closer look at an aeropyle:

aeropyles and plastron network

Aeropyles and plastron network

The two holes in the center of the image are aeropyles, little holes in the chorion that allow the embryo inside to get the oxygen it requires.  The exact path oxygen takes from the atmosphere to the developing insect is a little complicated and probably varies from species to species, but the aeropyles are where the path begins.  The number and arrangement of the aeropyles varies across species quite a bit.  Some insects have them distributed across the entire chorion.  Others keep them localized in specific areas (Google “pentatomid eggs” for some good examples).  Many aquatic insect eggs don’t have aeropyles at all and depend on oxygen flowing directly through the shell.  Some aeropyles have sieve-like covers over the opening and others are just big gaping holes like the ones you see in the image above.  There’s a lot of variation, but they all share a common goal: allowing oxygen to enter the egg.

Did you notice that the area within the polygons near the aeropyles looks kinda spongy in the image above?  That’s because the eggs in this species have a structure called a plastron network.  Plastron networks are meshworks made up of many tiny projections of the chorion.  This meshwork is thought to trap air against eggs when they are underwater so that they don’t drown.  Many terrestrial eggs have these plastron networks and this structure may allow them to survive accidental submersion for some time.  Water bugs also usually have plastron networks that may be responsible for their survival while they are underwater.  Lots of other aquatic insects that lay their eggs in water don’t have these structures at all.

The structures I mentioned above are the typical structures you find on most insect eggs.  However, you can find other structures depending on the species.  Giant water bugs absorb water from the environment and the water passes through a structure at the base of the chorion called the hydropyle.  A few other insects have hydropyles.  Other species will have structures to keep their eggs in place once they’ve been laid.  Still others might have horns or other structures that allow them to respire more efficiently.  Just like the animals growing inside them, insect eggs show a lot of variation in color, structure, and arrangement of the structures and can differ a lot from species to species.

I’m still taking entries for my contest for a few more days!  If you want to win the mug, be sure to leave a comment here for your chance.  The winner will be announced Wednesday.

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Unless otherwise stated, all text, images, and video are copyright © 2011 DragonflyWoman.wordpress.com

Notes from NABS Day 2

meeting logoEvidence for Overland Dispersal in a Flightless Aquatic Insect

Hello again from the NABS/ASLO 2010 meeting!  Today I’m focusing on Day 2 of the conference and my favorite talk of the day.  But first, two things I learned:

— Some aquatic insects are capable of moving a very long distance to get to new or better habitats.
— The person who designed the layout of the Tuesday poster session should be tarred and feathered for coming up with the absolute worst possible layout.  While I feel like my poster went over fairly well (I even had 2 judges tell me that it was very well done , giving me some miniscule glimmer of hope that I might win one of the tiny number of awards at NABS this year), it was a physically miserable experience.  The posters were arranged like this:

poster session

One of the two poster session rooms, the one my poster was in, before the poster session began.

The space was about 8 feet long and about 8 feet wide and each of these little alcoves held 6 posters each.  You could comfortably fit maybe 5 people in this space.  And THIS is what it looked like with 8 people:

poster session

The alcove in which my poster was located during the poster session.

I was forced to stand out in the aisle because I didn’t fit.  Wow that’s bad design!  Still, my scientific experience during the session was great once I got past the bad lighting, the inability of the AC unit to keep up (it was probably 85 or 90 degrees in the room – hotter than outside!), and the cramped quarters.  I got a lot of good feedback.  Considering this poster was the entire reason I came to the meeting, this is a good thing.

But back to my favorite talk of the day.  The title of my Day 2 favorite talk is at the top of the page and is probably easier to understand than yesterday’s if you’re not a scientist.  The talk was given by Kate Boersma, a Ph.D. student in Dr. Dave Lytle’s lab at Oregon State University.  The Lytle lab does some excellent research and Dave has been a star in the aquatics world since he was granted his professorship at OSU, so it’s no surprise that I liked Kate’s talk the best of the ones I heard today.  Plus, she’s a colleague of mine, a fellow giant water bug researcher, so you can’t go wrong.  She works on one of the same water bugs I study, the lovely Abedus herberti:

Abedus herberti mating

Abedus herberti mating.

Kate’s talk was about dispersal of this insect, or the movement from one habitat to another.  But before I get into the presentation, let me say a bit about dispersal in aquatic insects, especially as it pertains to insects in the arid (=dry) southwest.

Aquatic insects living in streams don’t really stay in one place.  They move around a lot, but there is a tendency for them to move downstream.  After all, simply losing your grip on whatever you’re holding onto in the water is enough to sweep you off into the current and far away from your home.  Invertebrates moving downstream by passive means (being swept along by the current), either intentionally or accidentally,  is called invertebrate drift.  Generally, moving downstream is something you want to avoid if you’re an aquatic insect.  Fish eat the insects and other organisms that make up the drift, so there is a high risk of predation for drifting insects.  Streams can also change a lot over their length, so it’s to an aquatic insect’s benefit to stay in the place that is best suited for it.  Insects CAN move upstream though.  They will crawl, or in some cases swim, upstream through the water.  Alternatively, many species with terrestrial adults are known to fly upstream to lay their eggs, thus ensuring that the population at the uppermost portions of a stream (the headwaters) remain stable.  Any movement of an organism from one area to another is called dispersal.

If an area becomes unsuitable for any reason, the insects need to move to another area if they are to survive.  This means dispersing.  This happens frequently in the arid southwest, but how insects move between habitats, the cues they use to signal that a move is necessary, and whether dispersal is limited strictly to up and downstream movements are still poorly understood.  Kate hopes to explain how Abedus herberti chooses to move to a new habitat, how far they can move, and in what direction.  And this brings us to the subject of her talk.

First she described the conditions in the area in which I also do my research.  We have a lot of streams, but many of them are dry most of the year (these are called ephemeral streams because they water only flows for a short time).  Even streams that flow most of the year can mostly dry out during the summer, leaving behind isolated pools of water into which the entire invertebrate population of the stream must go.  As these pools get smaller and smaller, it becomes stressful for the organisms living in them.  Abedus herberti is also flightless, so if the pool dris completely and they can’t find a new source of water, they die.  If they are able to instead move to another habitat nearby by crawling across the land, they might be able to avoid death and prevent the local extinction of populations within the area.  There is some genetic evidence that suggests this is possible, but Kate is the first person to really look into it.

Kate has been interested in which environmental conditions, which cues, prompt A. herberti to move from one habitat in search of a better one.  In her talk, she described a study she did recently.  She expected that pool drying would prompt a water bug to move from one habitat to another, so she set up an experiment.  She set up several opaque tubs filled with water that held smaller tubs inside them.  These inner tubs were assigned one of two treatments: either they were left dry or they were filled with water.  She then placed bugs inside the inner tubs, left them for a period of time (honestly, I didn’t get the time frame down, but it was something on the order of overnight or a week), and then compared the number of bugs that she found in the water-filled outer tubs in each treatment.  She discovered that more bugs moved from a dry tub to the wet outer tub than from a wet tub to the wet outer tub.  This suggests that the insects use pool drying as an excuse to leave the poor quality habitat in search of a better environment.

Kate also presented data on the distance that these bugs are able to move overland, though she did not collect the data herself.  Her labmates collected water bugs from several different pools, marked them, released them back into the pools, and then came back much later and recorded the location of the marked bugs they found.  They discovered that A. herberti prefers to stay in the same area, if not the same pool, in which they were found originally.  However, some had moved.  Of these, the females were found to have moved about 20 meters (just under 65 feet) while the males moved only 12 meters (about 39 feet).  The bugs clearly don’t move very far if they don’t have to.

However, Kate also showed a video that she happened to get through pure serendipity: a rather crispy looking male giant water bug who had left his aquatic habitat, had climbed into a dry streambed, and was hurrying downstream.  This was visual evidence that the bugs are able to move over land if conditions warrant the behavior.  She was also able to calculate a land speed for the bugs of about 4.6 meters (15 feet) per minute.  This is pretty fast for a one inch long animal!  She further calculated the maximum distance the bugs might be able to travel based on some data I had given her regarding they length of time the bugs can remain out of water.  Her calculations suggest that these bugs might be able to move as much as 6624 meters (4.12 miles) before they dry out and die!

So, Kate showed that overland dispersal can occur in Abedus herberti, that they use pool drying as a cue to disperse, and that while the bugs prefer to stay in one place, they occasionally travel across land for some distance in search of a better home.  Pretty neat, eh?  I thought so.  :)

Tune in tomorrow for another edition of Notes from NABS!

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Posts in this series:
Day 0 – Introduction to the Series
Day 1
– Invasive Crayfish
Day 2 – Giant Water Bug Dispersal
Day 3 – Dragonfly Captive Rearing
Day 4 – Integrating Service-Learning Programs into College Courses
Day 5 – Impact of a Small Preserve on Stream Health

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

More giant water bugs eating

I’ve been super busy with work recently and haven’t had time to put together one of my normal, long-ish blog posts.  But, I wanted to get SOMETHING up this week!  This will be short on words, but hopefully big on the wow value.

Several weeks ago, I wrote a post on giant water bugs eating and included a video of the medium sized species we have in Arizona (Abedus herberti) eating a mealworm that I gave it.  That post details how giant water bugs eat, so I recommend that you check it out for more detailed information on what you’ll see here.  Abedus herberti isn’t nearly as big as another Arizona native, Lethocerus medius, and while it’s mode of eating is still impressive, it’s nothing compared to what L. medius can do.  Species in the genus Lethocerus are the largest true bugs on the planet and are real powerhouses when it comes to taking down vertebrate prey.  These bugs are big, so they can eat really big things like snakes, turtles, frogs, fish, and birds.  So, in my insect behavior class we fed a goldfish to the Lethocerus medius we’d been experimenting with all semester, a goldfish that was about the same length and likely much heavier than the bug.  The bug hadn’t eaten for over a week to prepare it for the goldfish demonstration.  This was the result:

Now if that isn’t the coolest thing ever, I don’t know what is!  This right here should be enough to convince anyone that giant water bugs are the best insects one Earth.  (Okay, okay – so I’m a little biased!)  Now normally this bug would just sit in one spot and wait for food to swim by (they’re called sit and wait predators for a reason), but not this one.  He was so hungry he actually hunted down and captured his food before eating it.

Next up will be my one-year anniversary post.  I can’t believe I’ve been at this for a year already!  This calls for a celebration.  I might even give something away as a reward for sticking with me this long…

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