Archive | February, 2014

American Cockroaches

28 Feb

blattidae_american_cockroach_side_view

I sat in on a introductory entomology lecture about cockroaches this week, so this seemed like a good topic.  Above you see my least favorite insect and also my frequent friend and visitor for night time assays in the greenhouse this past summer, the American cockroach.

I like this picture because it shows off a lot of great cockroach adaptations: the flattened body for fitting through tight spaces, the head tucked defensively under the pronotum, with the eyes wrapped around the top of the head for good vision in this postion, the long delicate antennae for sense perception in the dark, and the cursorial legs for running at high speeds.

My feelings about cockroaches have evolved since I entered entomology, and while I still don’t welcome them in my house, I now consider them fairly interesting to observe in other places and I even keep a small colony of hissers.  I think I crossed a hurdle while I was desperately collecting insects for my class collection during my own introductory grad student course.  After months I had somehow managed not to encounter a single cockroach of any species, which left me down an entire order.  When I finally saw one of these large ladies scurrying across a pavilion floor I jumped on it with my bare hands.  (In terms of weird cockroach collecting methods this still does not top the dinner doggy bag incident.)

Go away or I will glow at you

7 Feb
Glow in the dark Elateridae: Pyrophorus

Pyrophorus sp. click beetle collected in Argentina. (aka Deilelater sp.)

Here’s a cool beetle I found a while back, all the way down in Argentina.  This is a member of the family Elateridae, the click beetles, so named for their snapping/jumping defense mechanism.  Click beetles are cool enough that I really ought to give them their own post, but for now I’ll just direct you to Ted McRae’s recent excellent post on the subject.  There are tons of species of click beetles, all pretty easily identifiable by their elongate shape, back pointed pronotum, and the mesosternal spine they use to go click.

This particular click beetle has an extra trick up its sleeve.

Luminescent, phosphorescent click beetle

Pyrophorus sp. click beetle with glowing eye spots on pronotum.

The glowing click beetles are a genus (recently revised into several genera) notable for the two glow-in-the-dark spots on their pronotum.  Several species are native to the Southern US.  In researching these beetles I find a mixed bag of explanations for why they glow.  The adult beetles bioluminesce at night, and this light, which can vary in color from species to species, is involved in species-specific recognition cues in mating, much like fireflies (Feder & Valez 2009).

The eyespots also brighten when the beetles are startled, suggesting a warning, anti-predator function.  Facultative aposematism (warning colorations that are only sometimes used) can be especially useful when an organism has different categories of predators, some of which will find it distasteful and learn to respond to warning coloration and some of which will not (Sivinski 1981).

Finally, both the larvae and the adult beetles bioluminesce and the light may also function as an attractant for small insect prey, particularly for the larvae.  (My source for this last bit is Wikipedia.  Make of that what you will.)