Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
Clickable Guide
Moths Butterflies Flies Caterpillars Flies Dragonflies Flies Mantids Cockroaches Bees and Wasps Walkingsticks Earwigs Ants Termites Hoppers and Kin Hoppers and Kin Beetles True Bugs Fleas Grasshoppers and Kin Ticks Spiders Scorpions Centipedes Millipedes

Upcoming Events

BugGuide is a National Moth Week Partner. How to add your National Moth Week 2021 photos. July 17-25.

Photos of insects and people from the Spring 2021 gathering in Louisiana, April 28-May 2

National Moth Week 2020 photos of insects and people.

Photos of insects and people from the 2019 BugGuide Gathering in Louisiana, July 25-27

Discussion, insects and people from the 2018 gathering in Virginia, July 27-29

Photos of insects and people from the 2015 gathering in Wisconsin, July 10-12

Photos of insects and people from the 2014 gathering in Virginia, June 4-7.

Photos of insects and people from the 2013 gathering in Arizona, July 25-28

Previous events

Thermonectus marmoratus

Thermonectus marmoratus
Sycamore Canyon, Santa Cruz County, Arizona, USA
July 31, 2003
Size: 10mm
Will a contributing editor please move this beetle entry to the family Dytiscidae? There isn't a listing for the genus Thermonectus and I'm unable to create one. Thank you!

as to size Aaron? I saw some diving beetles in Pima Canyon the other day that looked just like these. The ones I saw were on the order of ~3mm. Couldn't get a good photo with my camera.

Hi, Bob
This beetle is in the 10mm range as an adult

According to, the genus is "Thermonetus". Is this correct? I added a genus and a species page, so you could add the images, or I could do it for you.
Very neat looking beetles! I am used to more drab ones.

American Beetles...
has the spelling Thermonectus. I tend to trust that reference much more than since I have found many errors on other pages and Ross Arnett was the expert on North American beetles (and if he didn't write the Dytiscid chapter I'm sure someone who had great expertise did). I am by no means an expert on beetles but I thought I might give my two cents.

Sounds good. Thermonectus it is. I have seen it both ways all over the Internet, and I don't believe I will try to track down any original descriptions!
By the way, do any of you have any juicy tidbits on either the genus or the species? I know nothing of these beetles.

I know...
of a couple of studies, one that isolated the defensive secretion (mirasorvone) and one that studied diet preferences (they prefer dead stuff with thin larvae of aquatic insects). These are the citations:

Velasco, J. and A. Millan. 1998. Feedings habits of two large insects from a desert stream: Abedus herberti (Hemiptera:Belostomatidae) and Thermonectus marmoratus (Coleoptera:Dytiscidae). Aquatic Insects 20(2):85-96.

Meinwald et al. (too many authors for me to name!). 1998. Mirasorvone: A masked 20-ketopregnane from the defensive secretion of a diving beetle. Proc. Nat. Acad. Sci. U.S. 95(6):2733-2737. (you really have to like chemistry to read this one!).

Other than that I know they are also found in lakes and hot springs and this species is basically restricted to the western states.

I updated the page based on info in the two articles. So do you work with these beetles?

Silly me. Now I read your profile...
I saw that there is something on these in the proceedings of the 1995 Invertebrates in Captivity Conference, but my library does not have it.
Did you know that the predominant steroid is named for the actress Mira Sorvino?

So are these for public display?

A little bit of a late response...
Sorry for being tardy. Yes, these beetles are on display at Tulsa Zoo. We have an aquarium with about ten animals in it, and have created an area for egg deposition. We often see larvae in the water, and I've been collecting them as I find them in hopes of rearing them to adulthood. I'm actually checking in on this species account tonight to add a photo of the eggs, which I just saw for the first time today.

I work mainly with aculeate hymenoptera but I'm never opposed to a good beetle:-) Since my wife is still in school I have access to journals through her account. I'm afraid the only thing I can do is get the full text on to my computer and summarize the info in the guide page. I couldn't find open access to the articles through a web search. That's too bad, but it's the case with most journal articles. Since I have no affiliation with a univeristy at the moment getting a hold of literature is becoming a real problem for my paper on spider wasps, too.

Mira Sorvino...I wonder why. I wonder if one of the chemists knew her or maybe had a little crush on her. I guess it's no different than naming a bug after someone or someplace...although some names don't really roll off the tongue like they should [Anoplius acapulcoensis...Yuck!]

I'm not sure...
I've never seen it "Thermonetus," but that's not to say it's incorrect. Is there a definitive authority out there that can assist?

Comment viewing options
Select your preferred way to display the comments and click 'Save settings' to activate your changes.