Field Stories: Attack of the Giant Water Bug!

Today I’m going to share a story about an experience I had at my field site a few years ago.  It’s about a young scientist trying to do field work for her Ph.D. and a determined father giant water bug who took great offense at her attempt to remove his eggs from the pond for study in her lab.  This particular story has the makings of an excellent bad, B-grade horror movie, so I hope you will enjoy it!

For those of you who don’t know, Arizona is an area of high traffic for illegal immigrants.  We get all kinds of people wandering into our country from other locations, stumbling through the desert looking for a better life in America.  Unfortunately, it means we also get some hefty drug trafficking.  The area where I do my field work is a high-traffic area, so I always make sure I have someone with me when I do field work.  I also like to have another person with me in case I get stuck in the mud in bottom of the pond and need to be pulled out (see my post about my field site if you don’t know why this is important!).  On the day in question, I had a friend with me, another environmental physiologist who works on insect eggs.  I’ll call her K for the sake of this story.

me in Papago in wadersK and I made the 45 mile drive out to the pond.  We chatted about work and our lives on the way there and were in a generally good mood by the time we arrived.  I put on my very stylish chest waders (see image at right), and wandered out into the pond.

When I pull sticks out of the pond, it is common to find the father clinging to the bottom of the stick.  They frequently sit still for only a few seconds before dropping back into the pond.  Occasionally, one will hold on a bit longer and I’ll have to shake the stick a bit to get him off.  The emergent brooders are well-known for protecting the eggs they have fathered.  If you tap a stick with eggs on it, you can frequently get the water bug to rush out of the water and up the stick in an attempt to protect his eggs from predators.   They can actually be rather ferocious.

On this particular day, I pulled a stick out that had a male attached to it.  He didn’t come loose with my usual shaking method, so I wasn’t sure what to do.  I had a handful of sticks with eggs in the other hand, so I couldn’t just push him off the stick.  I poked him with one of the sticks in my other hand, certain that he would be startled and fall into the water.

Instead, he crawled up the other stick.  Fast.  Right toward my hand.  Doing that “How dare you mess with my kids!” behavior.  I started shaking the stick really hard, trying to knock him off, but he still kept coming for me.  Not wanting to be bitten (and not wanting him to screw up the eggs I’d harvested when he crawled over them), I whacked him gently with another stick and he fell into the water with a satisfying “plunk.”  I waded back out of the water with my sticks, and knelt on the bank to trim them down.

If you thought the story was over at this point, think again!  A few minutes into trimming sticks, I felt something scrabbling around my neck area, scrambling over the straps of my waders toward my head.  Something big and strong.  Something that felt suspiciously like a certain angry giant water bug that had already tried to attack me…  I asked K, “Whoa!  What’s on my neck?” as I reached up and flicked whatever was on my neck off.  I was horrified to see that what fell to the ground WAS the giant water bug!  He’d climbed all the way up my waders and had ended up inches from my jugular!  He was clearly out for my blood.  :)  I may have let out a little shriek of horror and K laughed.  She knew full well that she would have done exactly the same thing if it had come after her.

Site of this adventure!

Site of this adventure!

So I grabbed the persistent little guy and tossed him back into the pond, thinking that was that.  I went back to stick trimming and egg counting, but a few moments later, I heard K laughing.  “He’s coming back!” she said.  I didn’t believe her, but I turned around anyway, ready to be a sucker since she’d already made fun of me that morning.  Sure enough, there was the darned water bug, climbing out of the pond, onto the shore, and headed right for me.  Again.  Now this is where I think the B-grade horror movie would come in.  If the water bug was a couple of feet long, it would have been perfect – me sitting on the ground, helplessly scrambling to get up, while the giant water bug bore down on me!  You’d see him crawl onto me and a few scenes later, some random hiker would find my dead body, sucked completely dry, as ominous music played in the background.

In reality, I picked the bug back up and chucked him back into the pond.  AGAIN.  Surely he was finished trying to exact his revenge for stealing his eggs from him.  Hadn’t I clearly demonstrated that I was the bigger, stronger opponent in this confrontation?

Apparently not.  A few minutes later, the bug came for me again.  He crawled out of the pond once more and headed straight for me.  This time, I was finished with my sticks and was watching the shore.  I saw him emerge and let him get a couple feet out of the water, marveling at his tenacity, before I picked him back up, yet again, and tossed him back into the water,  yet again.  If there was an award for the most protective giant water bug father, this would clearly be the winner.  He was quite determined.

K and I packed our stuff up and went back to the car.  Who knows.  The bug may have crawled out again and started looking for me one more time, but we weren’t there to see it.  We joked all the way home about the incident.  We kept imagining the bug clinging to the back of the seat, ready to reach his raptorial forelegs around the headrest as he grappled with me, his sworn enemy, as I drove home.  That was one persistent little bug!

In the horror movie version of this incident, the giant bug would have indeed clung to the back of the seat, then slipped out of the car and into the house while I unpacked my gear.  He would waited until dark, after I’d fallen asleep, then attacked.  Neighbors would notice that they hadn’t seen me for a few days and call the police.  An officer would calmly open the door and jerk back in horror as a gigantic beast rushed past him, eager to find new victims as he wandered the streets of Tucson…


Text and images copyright © 2009

Biological Trade-offs, or Why Brooding is Bad For Dad!

In biology, we talk a lot about trade-offs.  This usually means that when something gets better in one aspect of an organism’s biology, something else suffers.  Consider a tree species in a forest and its ability to survive a forest fire.  Now imagine that this species almost always experiences one type of forest fire.  If it almost always encounters the same type of fire, it probably doesn’t need to hold onto any of the traits that allow it to survive other types of fires.  Those traits require resources that could go toward other things – getting taller, growing faster, making more seeds or leaves, things that will help it survive the fire it always encounters.  Over time, the tree adapts to this fire and loses its resistance to other types of fires.  But what happens when a new kind of fire comes along, one the tree hasn’t ever experienced?  How well will it be able to resist that?  Because the tree has adapted so that it survives the fire it has always experienced, it has lost part or all of  its ability to resist new or very rare fires.  In this scenario, there is a trade-off between wasting resources to survive an event that almost never happens and using those resources to better survive the one that happens all the time.

Almost every biological organism exhibits trade-offs at some level, from viruses and bacteria to humans and other mammals.  Giant water bugs are no exception.  There are at least two major trade-offs related to giant water bug brooding: egg size and brooding costs (check out my post on giant water bug parents for more information about brooding behaviors!).  Let’s talk about egg size first.

Lethocerus indicus eating a small fish

Lethocerus indicus eating a small fish

Giant water bug eggs are, well, giant!  For aquatic insects, they have particularly enormous eggs.  In fact, one researcher, Dr. Bob Smith of the University of Arizona, has suggested that the size of the eggs was what led to the origin of brooding behaviors in the first place (Smith 1997 – full citation available at the end of this post).  Smith suggests that the giant water bugs started off a lot smaller than they are now and probably laid their eggs in water like most of their close insect relatives.  Giant water bugs are predators, and to become more efficient predators, they needed to get bigger.  In order to produce a bigger adult bug, Smith suggests they either needed to add an additional instar or they needed to start from bigger eggs.  True bugs, including the giant water bugs, almost all have 5 instars, so it seems that it is hard to for them to add one.  So, that left making the eggs bigger.  The eggs increased in size, allowing the bugs to become bigger as adults.  Eventually, the eggs got so big that they were no longer able to survive underwater, probably because they couldn’t get enough oxygen.  So, brooding evolved because the eggs got too big to survive without help.

In this scenario, there is a trade-off between making bigger eggs that require care, but result in bigger adults, and making smaller eggs that result in smaller adults, but do not require care.  You know which side of this trade-off eventually won: brooding evolved to allow the eggs to get bigger, and the giant water bugs became the huge, fierce predators that they are today!

Another trade-off relates specifically to the brooding behaviors of giant water bugs .  Brooding is likely bad for the father water bug, but the eggs do not survive if they are not cared for.  A water bug father thus faces this trade-off: he can care for his eggs, but at a cost to himself, or he can abandon his eggs to protect himself, but at the cost of his offspring.  Either the eggs are going suffer or the father is going to suffer.  Usually, the father makes a sacrifice himself in favor of the survival of his offspring, though the occasional aborted egg clutch has been observed.

So just why IS brooding bad for dad?  This is a question that several giant water bug researchers have addressed and there have been many suggestions.  Three broad categories of brooding costs have been identified (spelled out in an excellent paper by Kraus et al 1989):

Abedus herberti

Brooding Abedus herberti male

1. Brooding decreases a male’s mating opportunities. A male who is brooding cares for only one clutch of eggs at a time.  This means that while he is caring for eggs, he does not mate with other females.  If he did not have to care for his eggs, he could mate with many more females.  Thus, brooding decreases a male’s opportunities to mate.

2.  Brooding interferes with a male’s ability to move around. A brooding male experiences decreased mobility compared to non-brooding males.  At the very least, he is stuck in one place while he broods.  A back brooder has eggs glued to his wings, so he is unable to fly.  An emergent brooder has eggs stuck to a immobile object, so he can’t take his eggs with him if he needs to move to another location.  Back brooders might also suffers further costs including increased buoyancy (though Kraus et al provide evidence to the contrary), slower swimming speeds, reduced ability to find and capture food, and reduced ability to escape predation.

Lethocerus medius

Lethocerus medius brooding eggs

3.  Brooding increases a bug’s exposure to predators. Giant water bugs are big and full of high quality protein.  Brooding males are likely at a higher risk of predation than non-brooding males.  Back brooders may spend more time at the surface and have an increased surface area while they are brooding.  Emergent brooders spend more time out of the water while brooding.  In fact, a brooding emergent brooder is right out in the open, visible to everything!  Most emergent brooders will also try to defend their clutch from anything that might try to take it away, including predators and the occasional graduate students who need their eggs for their research.

So, brooding males sacrifice mating opportunities, mobility, and safety from predators to brood.  One might then ask, why do they do it?  One simple reason: giant water bug eggs do not survive if are not cared for!  Biologists generally believe that the ultimate goal of all biological organisms is to pass their genes on to the next generation.  If so, a male water bug will do whatever it takes to ensure that his offspring survive, that his genes are passed on.  This tips the trade-off in favor of the eggs, to the detriment of the father.

Next time, I’ll share another field story, one about an amazing water bug father who fought to protect his eggs as I tried to collect them.  It would make a good premise for a B-grade horror movie, and just in time for Halloween, so tune in!

Literature Cited:

Kraus, W.F., Gonzales, M.J., and Vehrencamp, S.L., 1989.  Egg development and an evaluation of some of the costs and benefits for paternal care in the belostomatid, Abedus indentatus (Heteroptera: Belostomatidae).  Journal of the Kansas Entomological Society 62, 548-562.

Smith, R.L., 1997.  Evolution of paternal care in the giant water bugs (Heteroptera: Belostomatidae).  In: Choe, J.C. and Crespi, B.J. (eds), The Evolution of Social Behavior in Insects and Arachnids, Cambridge Univ. Press, Cambridge, pp 116-149.


Text and images copyright © 2009

Kraus, W.F., Gonzales, M.J., and Vehrencamp, S.L., 1989.  Egg development and an evaluation of some of the costs and benefits for paternal care in the belostomatid, Abedus indentatus (Heteroptera: Belostomatidae).  Journal of the Kansas Entomological Society 62, 548-562.

Giant Water Bug Parents

Now that I’ve made a quick detour to talk about ants and other stinging insects and the dragonflies at a local wetland for a few posts, it’s back to the giant water bugs!  Today I want to go over parental care in giant water bugs.  If you remember from my post on insect child care, giant water bugs use a special type of parental care: paternal parental care.  This means that only the father participates in the care of offspring, and it is a very unusual behavior among insects.  So let’s go over how the water bugs care for their eggs!  First, though, I need to provide a little background information about giant water bug taxonomy (the organization of biological organisms) so everyone can make sense of it all.

I’ve already gone over the order, family, and American genera of the giant water bugs in previous posts, so I’m not going to go over them again here.  (Please see my taxonomy page for more information if you get confused along the way.)  However, there is another taxonomic group that falls between the family and the genera that I haven’t discussed yet, one that is important when considering paternal care behaviors in the giant water bugs.  This group is the subfamily.  You can easily tell when you are looking at a subfamily, at least when dealing with animals, by the suffix -nae at the end of the name.  Most giant water bugs belong to two big subfamilies, Lethocerinae (which includes only the genus Lethocerus, the truly giant water bugs) and Belostomatinae (which includes everything except Lethocerus, usually the smaller, rounder, and/or less robust water bugs).  There is one genus, however, that is very rare and only found in a very small part of South America, HorvathiniaHorvathinia is so rare, in fact, that researchers don’t even know where to look for it in the wild or whether it does any sort of paternal care like its close water bug relatives.  Horvathinia is generally placed within its own subfamily, Horvathininae, but some researchers think it might belong to either Lethocerinae or Belostomatinae instead.  Time and more DNA analyses will answer this question, but for now we’re going to ignore it.  After all, we don’t know what sort of parental care it uses, so we don’t need to talk about Horvathinia more here.

So, why do we need to know the subfamilies?  There are two basic known types of paternal care in giant water bugs.  These behaviors are known collectively as brooding behaviors – the word brood refers to a group of offspring all cared for at one time – and they are divided along the subfamilial lines.  This means that Lethocerus, a lethocerine, uses a different brooding behavior than the belostomatines, such as Abedus and Belostoma.  Let’s go over belostomatine brooding first as it is generally more familiar outside of the entomological community.  This is Abedus herberti:

Abedus herberti

Abedus herberti

Isn’t he a handsome father-to-be?  This is one of my favorite aquatic insects – I think they are gorgeous, amazing insects!  Take a look at those brown, round things on this bug’s back.  Those are the eggs that this bug fathered!  The belostomatines are back brooders, which means that the males care for the eggs attached to their backs.  How to the eggs get there?  In the belostomatines, the male and female mate, and then the female lays a few eggs on the back of the male.  The male then insists that they mate again (more about this in the next post), and then the female lays a few more eggs.  Several hours later, the female finishes laying whatever eggs she has available (up to about 150 in A. herberti) and leaves the area.

The male cares for the clutch of eggs on his back in several different ways.  All of the belostomatines carry their clutches to the surface periodically.  This allows the embryos developing inside eggs to breathe more efficiently – it is a lot easier to get oxygen from the air than from the water.  (In fact, providing oxygen in this way may be the primary function of back brooding behaviors.)  In the the bug you see here, Abedus herberti, the father further cares for his clutch by doing push ups underwater.  The eggs are able to absorb some oxygen directly from the water, so the push ups are probably a way to stir the water around the eggs and help the developing embryos breathe more efficiently when they are submerged.  Other species of belostomatines will do other underwater behaviors.  Eggs that are abandoned (male belostomatines can abort their eggs if they aren’t developing properly) or deposited anywhere other than on the backs of the male never hatch.  In contrast, almost 100% of brooded eggs hatch.  Brooding is thus an obligate behavior, one that is necessary for the continued survival of these species.

Now let’s take a look at how a lethocerine broods and compare their behaviors to those of the belostomatines.  This is Lethocerus medius:

Lethocerus medius

Lethocerus medius

As you can clearly see, the eggs are not on the back of the male in this species.  Instead, the eggs are laid on a stick above the water line.  Can you see them?  If not, take a look at the stick below the bug – those light colored, rounded blobs are the eggs.  (You can see a previously hatched clutch under the back end of the bug as well.)  This bug obviously cares for his eggs very differently than the belostomatine we looked at above.  If he’s not carrying his eggs around on his back, how does he care for them?

Lethocerus medius is an emergent brooder.  This means that the eggs are laid on vegetation above the water line instead of on the backs of the males.  However, like in the belostomatines, the eggs still need care and will die without it.  Giant water bug eggs have likely been brooded for millions of years.  During that time, it seems they have lost most of their ability to retain water.  Lethocerine eggs that are left out of water without parental care dry out so badly that the embryo inside dies.  So, lethocerines, like the one you see here, care for their eggs by bringing them water.  The male will typically remain attached to the stick that holds his brood, but is usually found at the base of the stick underwater, using his respiratory siphon to breathe.  Every now and again, the male will climb up the stick to his clutch and let all the water on his body drip down onto the eggs.  There is evidence that suggests that the males of some species might also swallow water that they then regurgitate onto the eggs.  Once the eggs are nice and wet, the male then climbs back down his stick and waits underwater until he has to water his eggs again.

So there you have it.  One group of giant water bugs cares for their underwater eggs by bringing them to the surface to get air and the other cares for their eggs, which get plenty of air, by bringing them water.  Pretty cool, eh?  Next time, I’ll discuss some of the costs and trade offs associated with parental care in giant water bugs.  In other words, I’ll be talking about why brooding is bad for dad.  Stay tuned!


Text and images copyright © 2009

Insect Child Care

As humans, we take the care of children for granted.  If you have a kid, you take care of it until it is old enough to move out and live on its own.  Lots of other mammals care for their children in similar ways, teaching their offspring how to survive in the world without their parents.  But this sort of parental care behavior is very rare in insects.  The insects I study, the giant water bugs, have a very special form of parental care and I’ll talk about that in my next post.  Today, I want to go over some of the different insects that use parental care so that you might learn a bit about the different ways that insects can care for their young.

This is a carrion beetle (also known as a burying beetle):

carrion beetle

Carrion beetle

If you follow my blog, I’ve talked about this beetle before in my post about my mold problem in my insect collection, so it should be familiar.  Carrion beetles are some of the more disgusting animals in the world, at least as far as most people are concerned, so please skip on to the next photo if you have a weak stomach.

So how exactly do carrion beetles care for their young?  Let’s go through the process, keeping in mind that it works a little differently from species to species.   First, the male-female pair finds a dead animal.  This could be a mouse, a snake, a bird, a small opossum – anything that’s in the size range a pair of beetles can handle.  Let’s say the beetle above has found a mouse.  The beetle and its mate will pull all of the fur off, roll the mouse into a ball (often colorfully called “mouse balls” in entomological circles), and bury it to prepare the carrion.  The pair will mate and then the female will lay her eggs near or on the carrion.  When the eggs hatch, the larvae will feed on the rotting carcass and the parents often help them feed.  The parents also help make the carrion last longer by eating fly larvae (maggots) that compete with their young for food.  Some carrion beetles spit digestive enzymes on the carrion to keep it fresher longer and others will carry mites that provide this service for them.  In fact, the parents are so busy taking care of the carrion that it requires both of them to keep molds, maggots, and other organisms from completely taking it over and depriving their children of food.  If the parents are successful, the larvae will feed for several days to a few weeks and go through all of their larval instars, then drop off the carcass to pupate.  At this time, the parents abandon the nest and leave their offspring to fend for themselves.  So, carrion beetles care for their young from the egg stage until pupation.  They are also among the very few insect species that have this sort of bi-parental (two parent) care. It is very unusual for both the father and the mother to care for the young.

A more common parental care behavior is the sort you find in the webspinners.  This lovely creature is a webspinner:



Isn’t he gorgeous?  These are actually rather unusual insects that aren’t common most non-tropical (i.e. temperate) locations.  Many entomologists will actually never see one of these alive in their lives!  Luckily for me, Arizona just happens to be one of the places where they are very common, so I was able to get some photos of this webspinner on my back porch one afternoon.

Take a look at the forelegs and look at the tarsi, those little segments near the end of the leg.  See that one big oval shaped tarsus where the arrow is pointing?  This is a specialized tarsal segment.  Were you curious why these are called webspinners?  If so, here’s the reason: that specialized tarsal segment contains a silk gland.  Webspinners are actually able to make webs!  They don’t make webs like most spiders though.  They make long, tube-like webs, called galleries, underground or in a food source.  The galleries are where the parental care takes place.  A male and female webspinner mate in a female’s gallery.  The male leaves right away and the female lays her eggs in her gallery.  As the nymphs hatch, they live within the gallery of their mother under her care.  When they reach the adult stage, they may leave the nest to find another place to live (especially if they are males – they don’t stick around in their mother’s nest very long) or continue to live in the gallery, expanding it so that it fits more and more individuals.  This sort of parental care should sound very familiar, even if you know very little about insects.  If it’s not coming to you right away, I’ll give you a hint: ever see an ant farm?  Webspinner galleries are a lot like ant nests and the sort of care that they exhibit is very ant-like.  One female establishes a nest that can end up containing several generations of offspring.  Paternal care by a single adult female is relatively common among insects, especially in the social insects like ants, bees, and wasps.  But webspinners are rather different from the ants, bees, and wasps too – they don’t have one single female who produces all of the offspring in the nest.  The female who establishes the gallery originally produces a second generation and might produce several more, but the other females in the nest are all able to produce their own offspring as well.  So, to recap, webspinners use maternal parental care (the female parent cares for the young) and care for their offspring from the egg stage through adulthood, and even sometimes beyond!  This is very different than what we saw in the carrion beetles where both parents were necessary for the survival of the offspring and care ended as soon as the larvae pupated.

Now we’ve come to the really rare parental care behavior: paternal care, or care only by the father.  This sort of behavior is only known in a VERY few insects, including the golden egg bug (Phyllomorpha laciniata) and the giant water bugs.  I’m going to talk about the giant water bugs in more detail in my next post, so for now, check out the photo of the golden egg bug at this link:

(I apologize for not having my own photo, but these are only found in Europe and I’ve never been there.  I’m also not keen on stealing other peoples’ photos without permission.)  Did you see the gold colored eggs on the back of the male in the photo?  These bugs are, like SO many other insects, named after a characteristic they possess.  These bugs have bright gold eggs, so they’re called golden egg bugs.  So how do they care for their offspring?  This species is probably just evolving their paternal care, so it’s still a bit sloppy compared to the elegant system you find in the giant water bugs, but here’s the general idea of how the system is thought to work.  The eggs of these bugs have traditionally been laid on plants near the ground.  However, the vast majority of the eggs left by themselves are eaten by ants.  The females of this species are therefore starting to deposit their eggs on the back of other members of their own species, mostly the males, gluing them to the backs of these individuals so that they are protected from the ants until they hatch.  The bugs themselves don’t like having ants on them, so they’re inclined to keep the ants away from the eggs they carry as well.  Pretty neat huh?  The offspring thus benefit from the selfishness of the adult that carries them.  I call this a sloppy system because females basically have to ambush a mating pair to be able to lay eggs on their backs.  Most golden egg bugs really don’t want to carry the eggs and will try to get away.  Mating pairs have more important things going on and keep doing what they’re doing while another female lays her eggs on the male.  The male bugs then carry the eggs around with them until they hatch, at which point the egg shells fall off.  Golden egg bugs thus care for young only in the egg stage and then the nymphs are on their own.  Unlike the carrion beetles, only one sex usually cares for the eggs, and unlike the webspinners, the males are usually the caregivers.  In the giant water bugs, the other insects that use paternal parental care, the system is a little different.  The male and female mate, and then the female lays her eggs in a way that ensures that the male cares for his own offspring.  The females mate, lay their eggs, and leave.  The male is left on his own to care for the eggs until the nymphs hatch from them.

Paternal parental care is probably the most rare form of parental care known in insects, but all of the giant water bugs observed to date use this form of parental care.  Tune in next time for more information about the amazing parental care system of the giant water bugs and prepare to be dazzled and amazed!


Text and images copyright © 2009