Sexton Beetle, with Hitch-Hiking Mites

2010 October 9

I found this beetle in the bare ground next to our garage on August 10. It is similar, but not identical, to some that we found eating a dead mouse about three years ago:

This is definitely one of the Sexton Beetles, genus Nicrophorus, which are large and pretty distinctively colored carrion beetles. They are particularly known for their habit of not just eating carrion, but of mated pairs actually getting together and actively burying small dead animals so that they can have the corpse pretty much to themselves[1].

Based on the yellow fuzz on its back, it looks to be Nicrophorus tomentosus, which is the only species of sexton beetle I’m seeing on BugGuide that has fuzz anywhere other than the underside. It is also pretty dirty, but I didn’t clean it off because I didn’t want to dislodge the mites:

All those little mites crawling all over it looks pretty bad for the beetle, doesn’t it? If those were parasites, that beetle would probably be done for. Luckily for the beetle, they are not parasites. They are actually more like a detachment of Marines on a Navy ship.

They are Poecilochirus mites, and they are using the beetle as a transport. See, these mites eat the eggs and larvae of carrion flies, but they don’t have any way of getting from one piece of fly-infested carrion to another, what with not having wings and with carrion being pretty widely distributed. So, they hitch a ride on large carrion beetles, which will take them where they want to go.

Once there, the mites invade the corpse and start eating fly eggs. Carrying these mites is to the beetle’s advantage, too, because carrion flies are The Competition at the the corpse. So, if a beetle can offload a bunch of mites to clear out the fly eggs, there will be more carrion left over for the beetle larvae. Everybody wins! Except for the flies.

This isn’t the first time we’ve seen these mites, by the way: one of them cropped up in the pictures of theAmerican Carrion Beetle earlier this summer. The mites are evidently not dedicated to a particular species of carrion beetle, and will hitch a ride on pretty much anybody who’s available.

[1] As David Brady so eloquently put it over on Insect Picture of the Day back in 2007,

Carrion beetles need a tiny corpse, such as a dead mouse or vole, in order to reproduce. When they find one, they use pheromones to attract a mate. After mating, the male and female stay together until their young are raised. As with any healthy relationship, the first thing the young couple must do is hide the body. Over the next 24 hours, they bury the corpse and dig a crypt around it, stopping to mate, on average, about 70 times. (Ah, newlyweds!)

6 Responses
  1. October 11, 2010

    I am delighted to have found your site! The pictures are incredible, and the narritive is a good read. I was searching Google for photos of caterpillars to try to identify one I found. It was perhaps a TigerMoth Larvae. I live in SE Michigan, and look forward to reading your past and present posts. Thanks, SV

  2. October 12, 2010

    Glad you like it. Did you find out what your caterpillar was?

  3. October 13, 2010

    A link is on the way in a post scheduled later today. Awesome photos of the mites.

  4. October 18, 2010

    Wow – incredible macros shots!….to show the hitching mites – very cool…. Glad we stumbled across your blog from the Nature Blog Network. Happy to follow your entomology adventures 🙂

    We’re two traveling wildlife field biologists new to the network as well….

  5. barb quenzi permalink
    August 11, 2011

    Boy, you are really good!!! That looks like the suspect.

  6. October 24, 2012

    Thanks a lot for this!
    This actually helped me identify the mite that’s been living in my African snail tanks. I think they came in the moss I picked, does make be wonder what they’ve been feeding on in the tank in order to keep up a population in the tanks though.

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