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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