Tuesday, June 24, 2014

Backswimmer or Water Boatman?

Just a short post for “True Bug Tuesday,” addressing an identification problem that many people admit having. I am not an expert on aquatic insects by any means, but differentiating backswimmers (family Notonectidae) from water boatmen (family Corixidae) is fairly straightforward.

Backswimmer swimming upside down

My own experience has shown that backswimmers are generally far more commonly seen by the casual observer than are water boatmen. Backswimmers can even turn up in the fountains, swimming pools, and other artificial water environments water boatmen rarely frequent. Now, if you bother dragging a net through the water, especially over the bottom of a pond or slow-moving stream, then you may see water boatmen at least as frequently as backswimmers, if not more so.

Turn on lights at night anywhere near water and you may bet large numbers of water boatmen showing up, flailing about on the ground. Both water boatmen and backswimmers can fly as adults, but backswimmers seem to be mostly diurnal and will rarely if ever be attracted to lights at night.

Water boatman attracted to light at night

Physically, both kinds of insects do superficially resemble each other. Both are more or less oval or bullet-shaped, and the hind legs are very long, modified for rowing through the water. That is pretty much where the similarities end, however.

Adult backswimmers, at least those of the common genus Notonecta, are much larger than the average water boatman. Backswimmers, in cross section from front to back, have distinctly triangular bodies. They are shaped more like a boat than a water boatman. The top of a backswimmer is keel-like, affording it the ability to swim very rapidly upside down. Water boatmen are more flattened top to bottom.

Water boatman

The front legs of backswimmers are short, but shaped normally, with no obvious modifications. The front legs of water boatmen have spoon-shaped tarsal segments for scooping organic matter into the mouth of the bug. While backswimmers have a four-segmented rostrum (“beak”) they use to bite prey, water boatmen have the beak fused to the head. The face of a water boatman reminds one of an imperial storm trooper from Star Wars.

Water boatman. Note scoop-like front "feet"

Most water boatmen are brown on top, marked with fine, transverse black lines, giving them a slightly corrugated appearance. Backswimmers, by contrast, are usually boldly marked with patches of black, yellowish-brown, red, or white.

Top of backswimmer, © Lynette Schimming

Backswimmers frequent open water where they actively pursue mosquito larvae and other small aquatic insects. Water boatmen normally cruise the bottom, stirring up muck and microscopic organisms that they feed on. Consequently, water boatmen are often difficult to see when you are looking into the water. They are camouflaged, and/or they hide under leaf litter and other bottom debris.

Backswimmer, © Margarethe Brummermann

Look for backswimmers surfacing to take in air with those hydrophobic hairs around their rear end. The hairs also go down the middle of the underside of the abdomen, helping to trap air for their underwater lifestyle.

Source: Lehmkuhl, Dennis M. 1979. How to Know the Aquatic Insects. Dubuque, Iowa: Wm. C. Brown Company Publishers. 168 pp.

60 comments:

  1. Great blog with many interesting informations about insects!
    Greetings from Poland

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    1. Thank you for the compliment!

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    2. Thanks for this Eric. I live in the UK and have what I thought were Waterboatman in my aquarium. Given that they ate all my newtlets I now know they were Backswimmers.

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    3. Oh, Rupert, I am so sorry! I hope you are trying again with new newtlets.

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  2. Interesting. i'm not sure if what i seen is the same. My mother just called them " water bugs " but i remember the classical oval body with four dots on the water surface that sort of "slid" on the lake like an ice skate when they moved. but i never got in the water to check them out. lol and haven't checked water out in a long while. I think my hands are full with the bugs just inside this house.

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    1. Ah, you are talking about water *striders*, yet another kind of true bug that lives on the surface of the water, not underwater like these two.

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    2. A lot of these bugs are in my pool, where do they come from and how do I rid my pool of these critters?

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    3. They are capable of flying from pond to pond....Use a net to fish them out.

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    4. When I try to take the backswimmer out with a net, they just fly right back in the pool....

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  3. My friend's pool has water boatmen and they will bite you, just like a horsefly. They hurt. During the day, they were on the wall in the shade. If you stood there, they would come over and bite you on your back. I didn't see any backswimmers in the pool.

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    1. Excuse my polite but assertive disagreement with you. Water boatmen do *not* bite, and even backswimmers are usually non-aggressive. You may be describing some other aquatic insect. I'd have to see it to identify it, of course.

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    2. Great blog! I have lead many school groups and college classes to ponds and streams. I have yet to be bitten by anything other than mosquitoes and the occasional crayfish pinch. 20+ years...1 kid bitten...by a back swimmer. I had just given the safety talk when I heard a scream. A kid just 2 weeks in the country from Sudan...did not understand my safety talk and pushed a back swimmer past its limit.

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    3. Waterboatman may not go out of their way to bite, but try to handle one of the local Pennsylvania variety and be prepared for a bite and subsequent burn/itch you'd expecthink from say a wasp or white face hornet. Sure they may prefer to flee when disturbed but hold one in a cupped hand and it will let you know about yourself.

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    4. Hi, Erik. The next time I encounter a water boatman, I may have to experiment for myself!

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    5. I just picked on up out of my stock tank, held it between my fingers, held in my palm. Didn't get a bite. Jumpy little sucker though. Hoped out of my hand back into my sock tank.

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  4. Water boatmen are not aggressive but when cornered they definitely bite. I was bitten 2 days ago when one was in my towel. The bite is very swollen and red. I was bitten once years ago when I sat on one in a hot tub. It took a month to heal.

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    1. I am sorry you had a bad experience. Some kinds of backswimmers are smaller than the ones shown here. Water boatmen do not have the mouthparts to bite people.

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    2. What about stinging? I'm not sure, even with the descriptions given which I have in my pool, but I do know that when I captured one by hand I quickly dropped it after being either bitten or stung. It felt like a wasp sting. I have a picture but can't figure out how to post it.

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    3. Backswimmers can bite, and it does feel more like a sting.

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    4. I know the difference in both of these bugs and you are wrong. The water boatman bites!

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    5. With all due respect, I am *not* wrong. Thank you.

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    6. Amelia, this is very helpful, and you should not be ungrateful for this.

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    7. I was bitten by one of those creatures as a kid. Bloody hurt. Scooped it out of my neighbours pond and soon dropped it when it caught me. He'll of a bite on them.

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  5. hey thanks this info helped me answer a question in a class I am in

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  6. My friend had some water boatman swimming in her pool. After trying to pick one up, I can confirm that they do either bite or sting. This is in the Portland area, so I don't know if there are different kinds around the country.

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  7. I am curious what the difference is between the red and gray ones (male vs female?). They are 'luminescent' when they hide on the side of our faux-natural rock pool. I have both in my pool. Both bite. I scoop them up and squish them before they can fly back into the pool. They look more like your picture of a backswimmer. I am in Northern California.

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    1. Might be two different species. I do wish you would refrain from killing them. They are eating mosquito larvae in part, so saving you from *real* pests.

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    2. I was bitten 2 days ago on my back by a backswimmer in my pool. my daughter had to knock it off my back. it hurt a
      lot, now it has been swollen and very itchy, non-stop actually. I've seen them over the years if the PH levels were low, but this is the first time I've been bitten by one.

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    3. I'm sorry for your painful experience, Lorrie. I can empathize, I was bitten by one as a child.

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  8. the boatman that are in our pool sometimes, they definitely bite, absolutely no arguing that.

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  9. I encountered something today, I seen your blog and by the time I went out to take a photo ants had attacked it, I brushed them off and got a photo, I will post it here for you Bug Eric, and I will be so grateful for you to give me any information regarding this bug...

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  10. I know this is going to sound strange but I actually have an infestation of backswimmers in the crevices of the trunk of my car. I don't live by water however visited my daughter who has a marsh like river running through her apartment complex. Is it possible that the backswimmer made a nest? I just don't understand why they are in my car. I probably sleep about 10 to 15 per day out of the crevices of my trunk. But not in my trunk. Help... They are disgusting and I don't want them on my car and heaven forbid if they get in side my car

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    1. No, they do not make "nests." I wish I could offer you another explanation, but aquatic insects are not my specialty.

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  11. I made a short video of some I saw. I have never seen them before. They were dark brown... thank you for the info

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  12. Do water boatmen also have hydrophobic hairs?

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    1. Excellent question. I am not sure, but I suspect so.

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  13. Im not sure that I've had water boatmen in my pool but I've most definately have back backswimmers. They swim upside down with a dark/black underside and are light colored/whitish on their backs. I've been bitten by them a few times and even chased. To get rid of them one must scrub algae loose from ladders, sides of the the pool and bottom and vacuum out debris to waste followed by chemical treatment to all proper levels. Back swimmers are predators and feed on bugs that feed on debris and algae in your pool. Remove their food source and they will move on. Though they are nasty to us swimmers they are really the good guys eating insects, including water boatmen that are algae and debris eaters only.

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  14. Battling the same in my pool. Which one feeds on algae and the other feeds on that bug. Get rid of the algae they have nothing to deed on and will leave. They lay their eggs in the algae as well. My 1st time dealing with this in 5 years of owning a 35000 gallon pool. I'm beginning to get irritated. How do I submit photos?

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    1. As the post states, backswimmers are predator, waterboatmen mostly detritivores. Neither feeds on algae to my knowledge, but both can seek shelter there from other predators. I never offer "pest control" advice because pests are a human construct, they do not occur in nature.

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  15. I'm going through a problem where I want up with poison oak and it was hard to go away to get rid of it and meanwhile as it did go away I feel like my body is itching and I've been in a pool that's not really clean and I'm wondering if you were to get bit or stung can it give you a itching rash like like can it spread throughout your whole body

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    1. This is a medical question which I am not qualified to answer. I do hope you feel better soon.

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  16. I know these fellows well! Insects are one of my favourite kinds of creatures that God made, and they never get the kind of love they deserve. Actually, when I was a kid, I subscribed (well, my mom got it for me) to a science magazine that had an 8 page comic in each issue of a professor and a few kids who would shrink down to study insects. The water boatmen/backswimmers were one of them. **I just wish I could figure out what magazine that was as I would love to see it again**

    So, these two insects are totally different then? I mean, can they interbreed? I've wondered about this-I suppose they are different from your article, but if you can just confirm that, I would appreciate it

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    1. Yes, these are two completely different insects, would NEVER hybridize.

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    2. Gotcha. Thanks for replying!

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    3. By the way, the magazine I was talking about was Owl Magazine. And the comic was called "Mighty Mites"

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  17. I have a fascination with these little creatures mainly rooted in nostalgia. It’s interesting to know that what we called ‘swimmers’ in my friends pool growing up, are indeed backswimmers! I remember if I held them for too long I would get a ‘sting’ which now I know was a bite. They’re so cute to me and they actually look graceful when swimming. Like little seeds with legs 🥺 I have some insect tattoos and I’m planning to add a swimmer soon! Weevil of some type to follow. Anyways, thank you for the great read! 🐛♥️

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  18. Wait, the water boatman can also fly? As in, through the air...

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    1. Yes, the adults fly very well!

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    2. Wow this is news to me! I knew they breathed air but that's about all. I regularly pond dip with school children, I'll have to include that great fact and look out for them.
      Do they take to the wing straight from the water or climb to the edge do you know?

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    3. I do not know exactly how they exit the water to take flight. I suspect they must first gain purchase on emergent vegetation or something. They can certainly *enter* the water directly from the air.

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  19. Hello, thanks for your great information. How we can control them in aquaculture mud ponds both of them are in our area they attack carp larvae and we have big mortality when temperature raise and their community increase in water.

    We use some pesticides but they ar not effective.

    All around our farm ate rice farms and river.

    Thanks

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    1. I guess I need to pin some kind of post to this blog....I NEVER give pest control advice, and in fact recognize few insects as legitimate pests in the first place. "Pests" are an indication of human mistakes. They do not naturally occur. Thank you for understanding.

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  20. they WILL bite if you accidentally grab one or hit one while swimming. It stings like a hornet. And since it happened in our pool I know that was all that was in there.

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    1. You are definitely describing the backswimmer. Water boatmen do not have the right mouthparts for biting, and are seldom seen in pools unless they are heavily neglected, allowing algae and sediments to build up.

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  21. When I was young I got stung by a bunch of wasps when I was helping clear out an old palm tree, it hurt but nothing compared to whatever type of bite I got from a water bug in our pool. I'm not sure if it was a backswimmer or boatman but I remember it was fairly big and had "paddles" on the sides of it while it was swimming around and, me being the curious little kid I was, tried to push it under water with my foot and I felt it grab my toe and then a sharp pain. I just remember the pain felt much worse than the wasp stings and I never touched one again.

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    1. That would have been a backswimmer. I can empathize! I did the same thing once at summer camp when I was a kid.

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  22. When I was in 7th grade we had a science project to gather certain insects. There was a list of insects that do not pinch, bite, or sting, the water boatman/back swimmer was on that list. I had a kid pool in the back yard with a bunch of old water in it and there were water boatman/back swimmers in it. I looked for the biggest one and grabbed it. Wow, whatever it did to me hurt!

    That was over 30yrs ago, and I have never touched one since.

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    1. That would have been a backswimmer. I can empathize, I did the same thing once at summer camp.

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