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Diving Beetle - Cybister fimbriolatus - female

Diving Beetle - Cybister fimbriolatus - Female
O'Fallon, St. Charles County, Missouri, USA
July 23, 2011
Size: 30.5 mm --> (1.2 inches)
HiRes photo HERE.


I collected this water beetle in a movie theater parking lot back in July under a streetlamp at night. There's a small pond next to the parking lot.

I brought it home and placed it in one of our 30 gallon fish tanks containing two fairly sizeable goldfish. The goldfish and the water beetle don't seem to bother each other and they have lived peacefully for the past couple of months with no problems. Home sweet home for the water beetle, as it were.


The water beetle doesn't really seem to enjoy eating goldfish flakes. However, it absolutely loves dry cat food, especially the little red bits found in Purina's Friskies brand. It also readily devours crickets.


Anyway, off and on for the past couple of months, I have been wondering which species of water beetle it is. I haven't had any luck figuring it out on my own. So, I finally decided to try and get some photos of the hyperactive little bugger and upload them here for identification. This, of course, was no easy task!

I have heard it said that the only thing harder than trying to grasp a Dytiscidae with a pair of tweezers is trying to grasp Mount Everest with a pair of tweezers. Of this, I have little doubt!

Therefore, in an attempt to make the photo session easier on the subject and myself, I decided to place the hyperactive little bugger in the refrigerator for about 1/2 an hour, hoping to incite a hibernation-like response. It didn't work. The little bugger never slowed down! So, my photo session was not as controlled as I would have liked.

The water beetle was forever running away from the camera and diving off the coffee table and onto the carpet. Naturally, there are some carpet fibers that attached themselves to the water beetle and, unfortunately, showed up in the photos. I apologize for that.

Anyway, the water beetle is back in the fish tank and won't let me get near it with a net to redo the photo shoot. So, these photos will have to do for now.

Can anyone help me identify which species of water beetle this is?

Images of this individual: tag all
Diving Beetle - Cybister fimbriolatus - female Diving Beetle - Cybister fimbriolatus Diving Beetle - Cybister fimbriolatus Diving Beetle - Cybister fimbriolatus

RIP, Spunky
Just an update: Spunky the water beetle (as named by our 4-year-old daughter) passed away yesterday from what I assume was old age. She will be sorely missed. Hopefully, next summer we'll be able to catch another one. They make great additions to the fish tank and offer hours of endless amusement.

- Bill

Moved from ID Request.

fem. Cybister
experts will give you a sp. name

Thank you
That helps a lot! It most resembles a Cybister fimbriolatus. The bright green head and pronotal collar had me stymied for awhile, but the more I look at it and compare it with other C. fimbriolatus photos, the more I think it's just a slight variation/mutation of a local Midwest population.


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