Found a predacious diving beetle in a barrel of crayfish

[Eclipse]

I went out to a local supermarket where they had live crayfish for sale. While messing with them I thought I saw a nasty cockroach in there scurrying with them so I pushed the crayfish away with the tongs they provided. I picked it up with the tongs when I realized it was a beetle of some sort so I took it home. I noticed the feathery hind legs and the clumsiness in its ability to walk. I put it in a Tupperware container and added a little bottled water to it to see if it was some type of aquatic beetle and behold. It's a swimmer! Upon research I found out that it's called a great diving beetle (Dytiscus marginalis Cybister fimbriolatus thanks for the correction!). I read that it predatory to critters it's size and will also scavenge on dead carcasses, but this doesn't seem to be the case with mine.

I've had it for about a day and it doesn't want to eat anything I give it. I've lived here for a few years and I haven't seen these anywhere around creeks or ponds here so I don't know if I should let it go out here. Any suggestions?

 

[Lucanus95]

That's a Cybister sp. I used to keep a few of these years ago. Mine accepted fish flakes, prekilled guppies, and earthworms.

 

[pannaking22]

It could still be settling in, so I'd give it a couple days before feeding it. They're pond dwelling and pretty easy to keep, but you'll want to make sure the water doesn't get too dirty otherwise it could die.

 

[beetleman]

awesome find! it looks like cybister sp. not dytiscus either way they are great to keep,quite long lived also,i have right now for about 2 years and going strong,i keep mine in a kritter keeper couple inches of water some floating plants and that's it. try feeding crickets,floating turtle pellets(mine loves em) frozen bloodworms,silversides. don't worry it will take to eating in no time,hope this helps alittle,they are great beetles to keep.

 

[The Snark]

It could still be settling in, so I'd give it a couple days before feeding it. They're pond dwelling and pretty easy to keep, but you'll want to make sure the water doesn't get too dirty otherwise it could die.

Which recalls vague memories of keeping these. They are adapted predators with a limited environmental 'comfort zone'. Water turbidity and quality and light all possible factors.

 

[RTTB]

The adapted for swimming legs are very cool.

 

[The Snark]

The adapted for swimming legs are very cool.

Outright amazing. A classical example of evolution; an invertebrate emulating the fins of a fish.

 

[ChanTheMan]

Personally, I would give it a place to hide, such as fake plants. Good luck with the beetle friend.

 

[Eclipse]

Looks like Cybister lateralimarginalis, thanks for the correction guys! I am going to change the water to spring water or RO/distilled water instead of the mineral enhanced bottled water I have it in now. I will also look for some plants for it to hide in. I'll also try some pellets and dried baby anchovy to see if it eats. I noticed that it's trying to grab onto the small branch that I put in its tupperware, but it keeps spinning it around so I'll have to change that. I'll keep everyone updated!

 

[Jacob Ma]

Outright amazing. A classical example of evolution; an invertebrate emulating the fins of a fish.

Convergent evolution, to be exact. Very cool when evolution happens between two totally different organisms, and you actually realize what's happening.

 

[Eclipse]

Update: I tried feeding it fish flakes, turtle pellets, live and dead insects, pieces of shellfish and it didn't eat any of it. I saw a video of them chowing down on an anchovy so I bought some dried, unsalted baby anchovies and threw one in its tupperware last night and it was gone the next morning. I tried feeding it again tonight and I witnessed him grabbing and chewing on the anchovy. I walked by and it dashed to the bottom and is now refusing to eat. It's really shy compared to the ones I seen online. I'm assuming because it has no hiding spots. I will leave the anchovy in there until tomorrow and I'll try live fish next week or so. I really just want to see this thing go to town on a meal so I know it's going to live.

 

[Ghoul]

Cool find! I've often seen insects that enjoy living in or on water, like the great diving beetles, backswimmers, water scorpions, water striders, whirligig beetles, and cadisfly larvae with their pretty houses. Back when I was a kid there was a lake near our house and I'd always catch, inspect and release everything I could find. I rarely saw the diving beetles though, and they were super fast so when I finally caught one in my net I was proud of myself lol.
Also I'm pretty sure they can fly, which I guess some people don't expect water living bugs to do. I was surprised when my backswimmer turned around and flew out of my jar to the nearby lake... I opened the window for it when I saw what it was trying to do. So yeah, keep that in mind.