A Beetle Moves a Mouse

Carrion beetles on a rat

This long-dead pack rat, Neotoma floridana, from our well house gave us a chance to witness a major orgy of carrion beetles.  Roughly 40 were scrambling over the carcass with more underneath it.  The 10:1 majority were the common American carrion beetle, Necrophila americana, dull black overall with a yellow anterior pronotum and a central dark spot.  Mating pairs were common with a lot of partner switching.

There is surprisingly little detailed information online about this common beetle.  Wikipedia states "It lays its eggs in, and its larvae consume, raw flesh (particularly that of dead animals) and fungi. The larvae and adults also consume fly larvae and the larvae of other carrion beetles that compete for the same food sources as its larvae."  They are primarily active in daytime.

Nicrophorus tomentosus with mites (upper left) and Necrophila americana

In the writhing mass I could occasionally spot a gold-necked carrion beetle, aka tomentose burying beetle, Nicrophorus tomentosus, named for the dense yellow hair on its pronotum.  We wrote about them with an emphasis on the mites they carry extensively in this blog last October.  We will return to them below.

RCB - note tooth on femora

Occasionally in the swirling mass of beetles I got a glimpse of another beetle I hadn't seen before.  It stayed mostly under the rat and I finally caught one to photograph.  This was a red-lined carrion beetle (RCB), Necrodes surinamensis.  Aside from the orange markings they also have a distinctive  expanded hind femora with a large tooth.

 Bugguide says "Rather nocturnal and is found at lights, unlike related genera. Adults locate carrion and mate on or near a carcass. They feed on fly larvae there. Eggs are laid on soil near the carcass. Larvae feed on fly larvae and carrion and pupate in soil. Adults overwinter in under litter."

All of these carrion beetles have a foul smell (no surprise their considering their life style) but that is due to the defensive chemicals they produce like all carrion beetles and their larvae.  RCB is even more sophisticated.  "It can eject anal fluid as a spray rather than an ooze. The abdominal tip, which projects beyond the posterior margins of the elytra, serves as a revolvable turret by which ejections are actually aimed."  Unlike bombardier beetles who spray from a dedicated gland, the RCB is unique as its spray is from the anus, a mixture of toxin and fecal matter, adding insult to injury. * (Editor's note: the author is a retired gastroenterologist.)

Unlike the other carrion beetles, there is detailed information on RCB in this paper by Brett C. Rattcliffe.  While the details of how they feed on the fly maggot was too much for even me, it is interesting that they are frequently canabalistic on their larvae.

Just as I finished this blog, my nephew Jon found beetles on a long-dead mouse.  When he came back 40 minutes later, the carcass had been moved 2 feet and he could see it twitching.  He watched as a Nicrophorus tomentosus beetle (with the orange jagged markings) would scout ahead, then come back and get under the mouse and start moving it again.  Berndt Heinrich recently described their technique of crawling under the animal lying on their back and using their legs to propel the victim forward.

Jon called me to the crime scene and I videoed the action.  Warning: This video is very graphic- do not watch before eating.  See it here on Youtube. 

3mm fly and a small rove beetle

You can see most of the other insects that feed on carrion as described in this Entomologytoday.org link crawling on and in the mouse.  The mouse has lost lots of it hair already and several holes allow them access to the body cavity. In addition to the usual beetle suspects, there are metallic green blow flies, black and white striped Sarcophagidae flies, slender black rove beetles and a variety of small oval black beetles, ants, and lots of tiny orange 3mm flies that were flying in and out of the picture.

The Nicrophorus tomentosus beetles that are moving the mouse in little jerks are lifting 20 times their own weight, a prodigious feat, all done to provide a home for their larvae.  They will protect their eggs, parent their offspring and even may share a carcass with other beetles.  You have to love a beetle like that, or at least respect it.