Mating Ground Beetles

In the last two days, I've observed 2 pairs of black ground beetles (Pterostichus sp.) mating. As you can see in the photos, the smaller male climbs atop the larger female in order to mate.

Couple #1:

Coming back a couple of hours later, the pair were still mating. Who knows how long they had been together before that? Or how long the courtship phase lasted before actual mating took place?

Couple #2:
In these photos you can better see the region of the beetles' bodies which contains their respective reproductive apparatuses.

A simplified discussion of the general reproductive system of insects can be found at http://www.cals.ncsu.edu/course/ent425/tutorial/repro.html. Note: on this site, if you move your cursor over an underlined term, that part will turn red on the diagram to show its location. If you wish to read a very in-depth, scientific (but dated, 1932) study of specifically beetles' reproductive system, go to http://jcs.biologists.org/content/s2-75/297/49.full.pdf.

In basic terms, reproduction among ground beetles is sexual, with the females' eggs being fertilized by the males' sperm, which fuse with them. An interesting (and somewhat humorous) note concerning this particular pair is that when I lifted up the flower pot, looking for slugs, etc. but not for beetles, the motion startled the couple and the female scurried away with the male on her back! I couldn't help but laugh, because it all seemed so natural, as if they weren't in the middle of something, as if the female always carried her mate around. Of course I know that this was a purely instinctual reaction, and present survival almost always takes precedent over procreation, but it was quite funny all the same.

The male appears to have a little flap, a continuation of its "armor", which comes down over the end of its abdomen, as if to give it added protection from predators or rivals while mating. Unfortunately, this also conceals the mating itself, though as flush as the beetles' bodies are we probably couldn't see the actual genitalia anyway.