Tuesday, November 9, 2010

Mite-y Beetle Families

Click to enlarge
I came across several of these beetles when a rotted piece of firewood broke apart.  Their distinctive appearance makes them easy to identify as a Horned Passalus (Odontotaenius disjunctus),  a.k.a. Bess Beetle or Patent Leather Beetle for its shiny body.  It is a member of the Passalidae family.  It is unique in the family in its ability to stand freezing temperatures.  Unlike many insects species which are hard to separate, the horned Passalus is the only species in the family which occurs in the US north of Texas and Florida.

The Horned Passalus is the "largest showy beetle in the US". *  "The prontium (back plate of the thorax) is square with a deep middle grove, separated from a deeply grooved  elytra by a deep waist".**   It has powerful mandibles capable of chewing through oak but do not bite and can be safely handled (if handling beetles is your thing).

These  beetles and their families live their entire life in well rotted wood.  I call them families because they are a rather tightly knitted group.  The white grub-like larva cannot eat by themselves and are fed with food which has been chewed by the adults.  Their nutrients must include microorganisms, as the larva won't develop in sterilized rotted wood.

Adults communicate by stridulation (squeaky sounds made by rubbing body segments together), creating at least fourteen different calls.   I can picture a patient graduate student with a tiny microphone hovering over a rotten log, wondering what they are saying to each other.  I suspect they are saying, "Doesn't this highly educated, advanced biped have something better to do?"  Update November 2015-  Check out their stridulation at this link.  Recorded by Will, Kaiden and Hilton at the WOLF School. ****  

Mites under "chin"
Notice the mites on the underside of the beetle to the right.***  Many beetles carry mites as passengers.  This is particularly true of beetles that live underground or in dead vegetation. We discussed this in the blog about Sexton beetles.  You "mite" be even more interested in the beetle/mite association.  If so go to Macromites Blog.

Like a few other beetles, my friend has been on his back, unable to roll over without help.  I suspect that if you spent your entire life in rotted wood chambers with something to hang on to, you would consider learning to roll over a waste of time.  When I put him back in his log, I thought I heard him squeak out a "Thanks".

*      Beetles, Peterson Field Guides
**    National Audubon Field Guide to North American Insects and Spiders, p. 555.

***  "Passalids almost invariably have associated mites - several families of mites are found ONLY in association with passalids, and many genera and species are similarly restricted - suggesting a very long association between the two groups.   I know of no mites that are harmful to the passalids, although there may well be some (e.g. tracheal inhabitants)."  (Herper.com)
**** WOLF is a 5th grade school focusing on nature studies and conservation.

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