American Carrion Beetle

2010 July 24

S_ found this large (probably 2 cm long), distinctive beetle in front of our garage on June 12.

It is very clearly an American Carrion Beetle, Necrophila americana. I actually think that this beetle species has already appeared on this site, as a larva.

They have sensitive-looking antennae which would be very helpful for sniffing out dead animals and similar things. However, they don’t necessarily eat carrion themselves: BugGuide says that the adults actually mostly eat fly larvae that they find on the carrion. I’ve also seen them a lot just kind of randomly foraging around, and on occasion have found them in garbage and decaying compost, so they obviously aren’t dependent on carrion (although they do like it[1]). The larvae are reported to be more likely to eat carrion directly, although they will also cheerfully eat fly larvae and larvae of other carrion beetles. For that matter, we constantly see larvae of either this species, or a related species, rummaging about in the leaf litter where there is no evidence of carrion at all.

So, S_ was OK with the idea of letting it crawl on her hand to get a sense of scale (although she did wash her hands afterwards). When I was editing the picture, I saw something a bit unusual underneath it:

Maybe that’s just a part of its body, but it sure looks like some sort of mite hanging on, I can even see two legs. The thing is, just because a mite is riding doesn’t mean that it is parasitic (although it could be). A lot of mites are actually “phoretic” – they just ride around on larger arthropods so that they can get to their actual food source. There are a number of mites that eat fly eggs and young fly larvae, and so they ride around on carrion beetles, who take them directly to the fly-ridden corpses where they can eat them[2]. This is actually beneficial to many of the carrion beetles whose larvae mainly eat the carrion, because those fly larvae are their competition. If the beetles carry around mites that make it easier for the beetle larvae to get more food, then that is all to the good as far as the beetle is concerned.

[1] Once, when I was about 10 or so, we had a bit of a mouse problem in the house, and so there was a mousetrap set in my closet. As it turned out, I forgot about it, and never heard it when it went off. Some time later, I happened to look into the closet and saw that it had caught a mouse – which was completely covered with these beetles, who were busily stripping it down to nothing. It was pretty grotesque.

[2] Carrion is a very competitive environment. While it is a very desirable, concentrated food source, there are so many things that want to eat it that it doesn’t generally last very long. So there is a lot of effort expended to get there fast, grow quickly, and try to fend off competitors. And, sometimes it is easier just to go ahead and eat the competition.

4 Responses
  1. July 25, 2010

    *thumbs up* One of Robert W. Chambers’ short stories featured one of these, iirc. And another starred a corpse-loving butterfly

  2. July 26, 2010

    There might be one of the butterflies that is attracted to corpses eventually. There are black butterflies around that I sometimes see landing on animal droppings, and I expect that they would be equally attracted to decaying flesh. I’m not sure which butterfly they are, since I haven’t been able to catch one yet, but I think they might be Mourning Cloaks.

  3. July 29, 2010

    Steven den Beste did a great series of posts describing why oil was so hard to replace because of the energy concentration found in it. Your description of carrion brings that to mind. Carrion: the oil well of the insect world!

    I had never heard of mites using beetles like mass transit systems. Fantastic! This is why I love your blog so much. It’s like these guys are remoras.

  4. November 14, 2013

    Great article. I will be dealing with many of tnese issues as well..

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