Friday, June 22, 2012

A new habitat

If you want to expand your study of insects, and what rational person would not, the best thing is to visit a completely new habitat, where like as not you will find a completely new suite of insects.

Let me recommend a road-kill opossum.

One morning when I went out I found a freshly dead opossum on the road right in front of the house. It was not damaged externally, but I knew the longer it stayed, the more smashed up it would get, and the worse it would smell. So I carried it down the street fifty feet (there was no other house around) and dropped it about fifteen feet off the road on the far side, which was railroad right-of-way, so again no one would be offended by it.

You would think a dead thing in Arkansas in the heat of summer could make a whole neighborhood unlivable, but I had noted in the past that dead things didn't last any time at all. You and I may not look at it this way, but a dead opossum is a whole mountain of free meat, and unlike vegetable food, meat is pure concentrated energy.  A lot of creatures will want their share of it, and they each have their methods of getting it. Bacteria, for instance. For invisible things they are shrewder and more organized than you think. You know that after a few days a dead thing begins to stink, and you probably think that is some natural chemical product of the rotting process. It turns out that is not true. There is no part of the rotting process that necessarily results in a bad smell. The bacteria manufacture that smell, and make it as horrible as possible, to drive vertebrates scavengers away from the corpse, and save it for themselves. Bluebottle and Greenbottle Flies are their chief competitors, and within very few days these turn the corpse into a frothing mass of maggots, again too nasty for most other scavengers to deal with. But within those first few days there is an opening for a host of small creatures to get in on the feast, and I decided I would observe the process.

The next morning I went out there with my camera, sat comfortably by the opossum, and noticed that, for a corpse, it was already full of life. Not long after life stops there is some smell of death, too subtle for us to perceive, but small creatures all around begin moving towards it. First of all, it was already buzzing with Greenbottle Flies, and their eggs were already hatching out the first maggots. But soon big droning beetles were arriving. For some reason, many of the beetles that feed on carrion have shortish elytra with the pointed tips of their abdomens sticking out behind. The first one like this I saw was Necrodes surinamensis (the Latin names frequently have nicro- or necro- or Thanato- all meaning death).

Now here is how the competitive jockeying plays out. These beetles, like the flies, lay eggs, and their young feed on carrion. The beetles themselves do not feed on carrion, they feed on the fly maggots. In other words they are clearing out some of the competition for their larvae. Here is one gulping down a maggot, with the Greenbottle Fly looking on.

Here's another beetle, Oiceoptoma inaequale, with a similar life history. But if you look closely, you will see that this one arrived with a small load of tiny flies on its back. These flies, Milichiids or something related, feed on the fluids of dead animals, and their gambit is to ride on the backs of carrion beetles or robber flies or other predators, or sometimes hang out around spider webs, and when they are brought to oozing meat they climb off and grab their share.

Here's another, slightly more colorful, beetle in the same genus, Oiceoptoma noveboracense. Perhaps we need a bit more color in all this blackness.

Here is the only one of these you are likely to see away from a corpse. This is Necrophila americana, the American Carrion Beetle (a very common beetle, not to be confused with the endangered American Burying Beetle).

The odd pattern on the thorax of this rather large beetle is meant to mimic the yellow fur with a bald spot in the middle found on the thorax of bumble bees. You wouldn't believe it when you see it here, but when it is flying towards its next cache of carrion with a loud buzzing flight, you have to look very carefully indeed to see it is a beetle and not a bumble bee. There is one other thing to remark here. This beetle arrived with a load of lice on its back (you can still see one left just behind his head). These were not blood-sucking lice making his life miserable, these were predatory lice and he was delivering them to a place where they could feed on their favorite food, fly eggs. In other words, they got a free trip to the eggs, the beetle got some help eliminating flies from competing with its own larvae. You begin to see how programmed this whole operation is.

Various species of rove beetles were also attending. They carry the short elytra and protruding abdomens to an extreme. They fly in and then fold their wings up under the very short elytra with the complexity of folding the flag at sunset. Here is a rather handsome one, Platydracus maculosus.

Finally, here's a tiny fly, Prochyliza xanthostoma, that's quite comical to watch. It specializes on the dry skin that remains when everyone else is finished, or at any rate, that's what his larvae feed on. This is the male with his complicated head structure (which the female doesn't have). He stakes out a good territory on the carcass, because that's where the females will want to be, then battles off other males with ram-like butting contests.

Maybe there was more of interest, but by then things were getting higher than I could put up with any longer.

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