Giant Water Bug – Toe Biter

2009 May 30

[Scene: my office, afternoon of May 21. The phone rings]
Me: Hello?
Sam: Dad! Mom caught a GIANT WATER BUG! She tried to pick it up, and it GRABBED her! She shook it off, and caught it in a DIAPER! We put it in a jar! It’s GIANT!
Me: Wow!
Sam: Well, OK. Bye! [click, hummmmmm][1]

Sam and her bug in a jar

Sam and her bug in a jar

A minute later S_ called back to give the details, and Sam had the story substantially correct. They had just pulled out of the grocery store parking lot, when S_ saw what she thought at first was a small bird fly by, until it landed on the road [2] in a very un-birdlike way and she realized it was a very large insect. So she jumped out of the car[3], and caught it pretty much the way Sam described. Then she drove home with the diaper-wrapped[4] bug in one hand, feeling it squirm around forcefully from time to time. Once they got home, she popped it into a mason jar with a screen lid, and that’s about the time that Sam called me.


Sam wanted to keep it as a pet, so once I got home, I took Sam to Wal-Mart and picked up a small 1-gallon aquarium kit. We also picked up a feeder goldfish. Then we set up the tank, made sure the lid was on and the aerator was working, put in the water bug and the goldfish, and watched.



Nothing much happened for a long time, other than the fish swimming around and the bug periodically moving from one perch to another, and finally we went to bed.

The next morning around 5:00, I heard Sam yelling from her room, so I went to see what was wrong. At first I thought she’d been scared by a bad dream, but then I realized that . . . something . . . was making a scrabbling noise from her yellow toy bin. So I went over to look, and . . . there it was. The giant water bug was in the bottom of the bin, scrabbling to try and get out. The thing is, Sam’s room is at the extreme other end of the house from where the aquarium is, so the bug had to get out of the aquarium (by squeezing through the opening in the lid that the aerator tube passed through), then fly the entire length of the house, then crawl under Sam’s door (which was closed), and then fly again to fall into the toy bin. It’s easy enough to see how it did it, but the why is another question.

Anyway, I got it back into the aquarium easily enough, and put a largeish rock on the lid to keep the bug from getting out again[5]. Later that morning after I’d gone to work, the bug finally took an interest in the goldfish, and ate it. S_ got some good pictures of the event. She says that the bug first bit the fish in the eye, which I expect dissolved its brain[6] and killed the fish almost instantly.


Then it settled down to inject digestive fluids into the fish body proper and suck out its insides. S_ says that it would stab a spot, suck for a while, then move to another spot and start again while the fish gradually deflated.


So. This is clearly a giant water bug. Given the size (about three inches long), it is most likely one of the six species in the genus Lethocerus. I think it’s either the regular American Toe-Biter Lethocerus americanus, or maybe the Eastern Toe-Biter, Lethocerus griseus. There’s supposed to be a groove in the front femur of Lethocerus americanus that is characteristic of the species, but I can’t quite tell if it is there or not. Giant water bugs are among the largest insects in North America, and reportedly quite tasty (the ones in Asia are even bigger, and are often eaten). The ones in North America live for about two years, starting out as small nymphs that prey on other small arthropods, but eventually graduating to eating minnows by they time they reach adulthood. They overwinter as adults (which is why this one turned up so early in the year), and lay their eggs in the spring and summer. In some species, the females lay their eggs on the back of the male, and he looks after them until they hatch, but other species lay their eggs on weeds in the water.

The giant water bugs do not breathe water, they trap an air bubble under their wings and breathe from that. Periodically, they will refresh their air supply by poking the tip of the abdomen through the surface, pushing out the stale air, and pulling in fresh air, like it is doing here:


That air bubble makes them very buoyant. Ours has to either swim hard, or hang onto something to stay submerged, otherwise it pops right to the surface. Once it gets out of the water, the skin is so water-repellent that the water beads up and runs off immediately. They fly pretty strongly, and given how we found this one, they are obviously pretty mobile – the nearest body of water substantial enough to support appropriate prey for a giant water bug was about a half-mile away from where it was found.

They make pretty cool pets, but I’m not so sure I would say they are good pets. Keeping it in goldfish is a bit more expensive than keeping a spider supplied with flies and crickets, and they are really prone to escaping if there is any opening in the lid of the aquarium that they are kept in. And the way that they get around the house once they escape, combined with the potential for a very painful bite if you, say, step on one, suggests that maybe other arthropods are a better choice for a pet.

UPDATE: I was given a dead (but fully intact) giant water bug to photograph in March 2012, and here are some more-detailed pictures of particular parts of its body that we didn’t get a good view of with the live one.

[1] Phone conversations with a 3-year-old can be a bit abrupt.

[2] We have the ideal conditions for road mirages right now (pavement heating in the sun with cooler air), so it often looks like the pavement is covered with water. S_ thinks that the bug mistook a road mirage for a small pond, and tried to land in it.

[3] Interestingly, nobody in the cars stopped behind her blew their horn at her or anything. I expect they were probably sitting there watching, and wondering “what on earth is going on there?”

[4] Yes, it was a clean, unused diaper. It was for Sam’s younger sister, incidentally.

[5] At the time, I thought that it had pushed the lid up and squeezed through, so the rock seemed like a good idea. But then, it got out again the next night, so I checked more carefully and found that the hole in the lid was wider, and the bug was narrower, than I had thought. So, we covered the hole in the lid with tape, and now the bug stays inside at night (although it still crawls up and claws at the lid when it gets dark).

[6] Like assassin bugs, giant water bugs inject digestive fluids into their prey to liquefy the insides, and then suck up the resulting slurry. Their bite is reputed to be extremely painful. Not so much because it is an actual venom[7], but because it is dissolving your flesh. This one later ate a second goldfish, and did the same thing – stab through the eye first, then go to the body proper. So, it looks like biting the eye first is no accident, but is a behavior evolved specifically to kill the fish as quickly as possible.

[7] Venoms, like bee venom, often have compounds that specifically cause pain by activating your nerve endings, but a lot of venoms don’t actually cause all that much gross physical damage to your tissues. Giant water bug bites are not like that at all. They are more like an internal acid burn.

107 Responses
  1. Larissa permalink
    May 7, 2013

    I recently went outside to get some fresh air when I heard a scratching noise by my recycling bin. So I snuck up to it thinking it was a mouse. Looked inside and there was a giant water bug inside of it. I was so grossed out! Took a picture and went inside. I have 2 kids. 18 months and 8 years old. Hope to never see another one around here and hope it dies in the bin.

  2. megan permalink
    July 2, 2014

    Well about three days ago my neighbor found one of these in a bucked behind his house. He had no idea wat it was and immediately brought it to my parents for help. Them knowing that I was going to college did summer to become a zoologist immediately woke me from my nap as a “test”. I quickly researched it n found out wat it was. My neighbor agreed to let me keep of n study it. I named him Luciser cause my friend believed it was like a mini Satan lol. Well we feed him snails n beetals but went n bought him a small goldfish yesterday. Well long story short we watched him eat it just as everyone said they would, but he shortly died about 2hours after feeding. Can anyo e tells us why?

  3. July 2, 2014

    One possibility is that the place you bought the goldfish from might have been medicating them with something toxic to insects. Perhaps treating them for some type of arthropod parasite? You could ask them, although I’m not sure if they’d admit it if they were.

    It is also possible that it was just a coincidence, sometimes insects that we keep as pets just die abruptly for no obvious reason. But 2 hours after eating the fish is awfully close timing to be completely random.

  4. angela mcwilliams permalink
    July 26, 2015

    I found one of these in Oklahoma city Oklahoma. I don’t know what to do with it?

  5. Bug Barb permalink
    July 26, 2015

    You should NOT hold it or handle it with your hands!!!!!!
    The bite HURTS a lot, so I’m told.
    That’s why their nickname is “TOEBITER”.
    It has a single fang-like thing that it uses to fill its prey with venom.
    If you have a small aquarium or a large jar, fill it with non-chlorinated water.
    Put a piece of styrofoam or wood that will float, so the bug has something to grab onto.
    Place the bug in the aquarium/jar and put a lid on it.
    If you don’t have a lid, plastic wrap will do, just poke a bunch of holes in it for air.
    Feed the bug crickets or small fish alive.
    It is a fascinating bug to keep.
    It is really cool if you get a male with eggs on his back.

  6. Debbie Middleton permalink
    September 7, 2015

    These giant water bugs have moved into our pond and are killing our baby koi. Any suggestions on how to capture or eliminate?

  7. Bug Barb permalink
    September 8, 2015

    They like to ambush their prey, so eliminate hiding places, if you can. Don’t reach under the floating item to remove it, the bug might be lurking there. Get a small net and hunt them down. Or you could go buy a bunch of cheap, rosy red minnows or goldfish. When you see one being eaten, just scoop it out with a net and step on it. If you see a large adult waterbug with weird things on its back, act quick. It is a male covered with eggs that will soon hatch into about 60 baby predators.
    Good-luck and keep us informed.

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