Sunday, September 30, 2012

Thinking about the blogs I didn't get around to writing.

Our usually uneventful lives have been very busy the last few weeks preparing for a class on insects we were going to be giving at the Arkansas Audubon Society's Adult Ecology Workshops at Ferncliff, just west of Little Rock. From time to time during this preparation I noted things around our yard I thought might have made an interesting blog, but I didn't have time for them, and now their brief moment of timeliness is past.

Well, the class is behind us and we are ready to start up again, but in the meantime the season has broken, and insect activity is rather quickly winding down. I haven't done this blog in winter yet, and wonder what I will find in the down-season to report about.

For now there is still a lot around. I might begin with a few things we saw at Ferncliff. We would do some classroom work on insect ecology, then go outside looking for some insects that were acting out what we were trying to talk about. Unfortunately the people running the facility where our group was staying were very keen on tidiness, mowing the grounds right to the water line of their lakes, and even carefully mowing the ditches beside their trails, so that nothing resembling a weedy wild flower was allowed exist. This made us a bit frantic to find something living. Fortunately there is one little strip amidst the concrete works of a road overpass where perhaps their mowers couldn't reach, and this was allowed to grow wild with goldenrod and asters and other late season plants. Every year when we have come we have found such interesting insects in that little spot it makes us realize what a special place the whole large camp could be if they would only ease up on it a bit.

One of our topics was predatory insects and the vital work they do trimming back insect populations and keeping them within the bounds that their environment can support. We took our class up to the strip on the overpass and quickly found two of my favorite robber flies. The hundred or so species of Arkansas robber flies space themselves out over the warmer months of the year, so that some species emerge as early as February, the greatest number of species are out in mid summer, and then a few are still emerging as late as November. These we found were late-emerging species, and in common with other late-season species, they were black (in order to absorb heat on cooler mornings) and they were both very hairy (to keep in the heat once they absorbed it).

The first we found was Efferia pogonias (unlike showier and more noticeable insects, robber flies have never received common names). They are such efficient hunters you seldom see them without prey, and this one had just stabbed some sort of plant hopper.

The second robber we saw needs a little more discussion. It was Laphria affinis. There are several species of robbers in the genus Laphria, and they tend to be very convincing mimics of bumble bees. Most of the species emerge in spring and early summer (our subject here, L. affinis, is anomalous in coming out late in the year), so that, just as with late season species, it is useful for them to be black and have lots of insulating hair. But that is not the main reason they look like bumble bees. Numerous insects disguise themselves as bees and wasps because everyone and everything knows that bees and wasps have nasty venomous stings. Many predators stay away from them, or handle them in such a gingerly manner that they get a few extra chances to escape. That would be an example of Defensive Mimicry: they look like bees so they are less likely to be attacked.

But there is a second possibility: Everyone knows bumble bees have stings, but everyone also knows that unless you deliberately annoy them, they are just big bumbling good natured oafs, perfectly harmless. Can it be that Laphria imitate bumble bees so they can cozy up to the insects, bees for instance, that  they feed on, that they are, in effect, robber flies in bumble bee's clothing? This then would be a question of Aggressive Mimicry.

I myself have always subscribed to the Defensive Mimicry argument. For one thing you almost always see bumble bees in and around flowers, and you almost never see robber flies around flowers, which is where they would go if they wanted to cozy up.

But this Laphria affinis was such a good mimic that when we first saw it, sitting near some flowering plants, we thought it was a bumble bee, and only long practice at observing robber flies made us stop and take a second careful look and realize it was a robber.

And then when it flew we wavered again; the flight was exactly like the flight of a bumble bee, slow and hovering, flying to the flowers and looking them over as though looking for one that still had a load of nectar. The buzzing sound of the flight was exact. When it landed, it landed clinging heavily to a cluster of flowers.  Absolutely brilliant.

Before our admiring eyes, and quicker than we could really see it, it snatched one of the dozens of soldier beetles clambering on the flowers.

I'm now at least a little more tending to be a believer.