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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"|
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.