Pit trap success - Common Black Ground Beetle -Pterostichus Genus

Beetle in insect pit trap
Photo by Brad Sylvester
copyright 2011, all rights reserved

On the first morning (August 4, 2011) after installing several very small pit traps in the forest floor in my backyard, I have met with success and captured a bug, a beetle to be more precise. It fell into the trap and appears unable to gain purchase on the smooth walls to crawl out.

The benefit of using these straight walled containers as opposed to undercut glass jars is that I can lift them straight up out of the hole without disturbing the hole. Then I can cap it, place a replacement container in the existing hole, and return to a more convenient observation area to figure out just what it is that I've caught.

Straight-walled pit trap containers slide in and out of
the hole easily for emptying and replacement.
Photo by Brad Sylvester, copyright 2011, all rights reserved

This specimen is clearly of the Order Beetles or Coleoptera. How do I know they are beetles? Well, once again, I'm going to say there are exceptions to the rule, but most beetles have a specialized set of wings that act as wing-covers to protect the wings they use to fly when not in use. The wing covers are generally hard and chitinous and when folded back in non-flying position, they completely cover the softer hind wings. The wing-covers or specialized fore-wings usually form a very straight line right down the middle of the beetle's back where they meet. The exception to the rule is a few species that have only vestigial traces of wings left and these might be a little harder to identify as Coleoptera right off the bat.

Also, I didn't know this, but bugguide.net assures me that Coleoptera or beetles, for the most part, have exactly 11 segments in each antenna. Some of my photos of this specimen are just barely clear enough to make out that there are indeed exactly 11 antenna segments present.

So then, we have all manner of sub-orders to choose from: Scarab beetles, water scavenger beetles, whirligig beetles, ground beetles... Wait a second, This beetle was captured on the ground among leaf litter, let start with ground beetles and see if we can find a match. Almost instantly we find the Common Balck Ground Beetle photo in the Audubon insect field guide. This is an approximate identification as there are many species that fall into this genus (Pterostichus). 180 species of Pterostichus have been identified in North America according to bugguide.net.

As is my usual motus operandi, I photographed this insect from a variety of angles and then let it go. Planning to do the identification from photos alone. In this case, my photos just aren't clear enough in the areas they need to be to make a positive identification of the exact species. There are many that can be ruled out, but the best we can do is drop this one into the Pterostichus genus and leave the species unresolved.

Common Black Ground Beetle (Genus: Pterostichus)
Photo by Brad Sylvester, copyright 2011, all rights reserved

I can also learn to keep the specimen until I make sure I have covered the identifying field marks either visually or in well-detailed photos.

Quick Facts about the Common Black Ground Beetle:
Diet: soft-bodied insects
Range: depends on the species, but Pterostichus can be found throughout North America
Habitat: varies a bit by specific species, but many are found in deciduous forest leaf litter and under rocks and logs. A few species can be found in planted fields (where anything that eats caterpillars is generally considered beneficial...)
Lifecycle: Common Black Ground Beetles lay eggs shallowly in the ground during the summer. They hatch into larvae in the same year and the larva hunkers down to wait out the winter when it gets cold. They will pupate and metamophosize into the adult beetle form from July to August depending upon region and species.
Lifespan: No information found, but there is also no mention of the adult beetle successfully overwintering (in New England) so it's likely these live from about July to at least the first hard freeze in November of the following year or roughly 15-16 months.
Activity: Bugguide.net says they are active in the daytime and thus are diurnal. This specimen fell into the trap between dusk and 9:00 am (which certainly allows daylight enough for them to be diurnal).