Monday, December 3, 2012

Earwig Look-alike

At first glance, it's easy to confuse the Rove Beetle (order Coleoptera) with the Earwig (order Dermaptera). I mean, their bodies look so similar, except that the Rove Beetle doesn't have menacing, pincer-like cerci jutting out from the end of its abdomen. However, they belong to distinctly different taxonomic orders.

Here is a comparison of diagrams:
Rove beetle. © 2004 Ken Wildman. 

Earwig, side view. Drawn by Sam Tremain, 2010. 
And of photos:

European Earwig (Forficula auricularia)
Rove Beetle (family Staphylinidae)






So, while there are other differing characteristics between the two insects, the presence (or absence) of forcep-like cerci is a good rule of thumb for identifying casual sightings. (Note that the earwig shown is a male, having curved cerci, but females, distinguished by their straighter cerci, still look quite different from rove beetles. Note also that other families of rove beetles do NOT resemble earwigs much at all, so it should be easier to identify them).

That being said, it can nevertheless be difficult to narrow the ID down to a precise genus and species. For this rove beetle, I'm conjecturing that it is perhaps Platydracus fossator, the Red-spotted Rove Beetle (although many have orange spots). This species is a member of the subfamily Staphylininae, or Large Rove Beetles (tribe Staphylinini, and subtribe Staphylinina). However, it could instead belong to the subtribe Philonthina and be the species Philonthus caucasicus. What do you think? If you can identify this Rove Beetle, I would be grateful for any suggestions. Here are the rest of the photos:


The main features I focused on in my attempt to ID this specimen were the size, shape, and color of the abdomen, pronotum, and elytra. Obviously the red coloring of the elytra serve as a distinctive marking for this Rove Beetle. I felt that the two species named above were the best fits, but I could be going in the wrong direction with those. So if you can provide any information, I'd appreciate it.

Also, if you'll recall, I posted some photos of a fearsome-looking beetle larva. Well, I suggested that it could be the larva of a Rove Beetle. Therefore,

this...


...could have come from this:


I'm intrigued now to see if I come across any more of these adults or larvae.

References:
http://entomology.ifas.ufl.edu/creatures/misc/beetles/rove_beetles.htm (rove beetles of the world)
http://www.plantsolutionsnj.com/good-bug-rove-beetle-or-bad-bug-earwig/ (rove beetle vs. earwig)
http://bugguide.net/node/view/326636 (Philonthus caucasicus)
http://bugguide.net/node/view/24118 (Platydracus fossator)
http://www.kenwildman.com/insects.htm (source of rove beetle diagram)
http://bugguide.net/node/view/31277 (Staphylininae)
http://www.biology.ualberta.ca/bsc/ejournal/bnkmm_12/otherpgs/pglst.html (table of contents)
http://www.biology.ualberta.ca/bsc/ejournal/bnkmm_12/otherpgs/collection.html (specimen collection)
http://www.pbase.com/tmurray74/rove_beetles_subfamily_staphylininae (specimen collection)

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