|Longhorn Bees, Melissodes paroselae|
The bees or wasps cluster conspicuously on free standing plant parts, and it is difficult to see the advantage that this behavior entails. I was tempted to call it 'bachelor parties' in the title, but yesterday at the Santa Cruz River in Marana I watched a group of Sand Wasp males come to rest on a twig of Burro Weed: No partying going on.
I found the sleeping place by following several slow-flying wasps that caught the evening light very nicely. They led me to clump of wasps that were already settled. The newcomers picked a place, shuffled and pushed their neighbors a little, sometimes had to fly up again and find a new spot, but then immediately became very quiet and non-responsive. To collect one, I simply pushed him into a vial. No protest from him or his neighbors. Alcock had observed the same passivity towards a Bee Assassin Bug who just came and collected his victims while the others slept on.
|Bee Assassin, Apiomerus flaviventris|
Yesterday I filmed the landing of several new arrivals in the sand wasp group and noticed in the video that at least two stuck out their proboscis repeatedly. They didn't seem to actually lick anything, so what were they doing? I am aware that the chemical sense of insects is not limited to their mouth-parts but is located on the antennae and even the pads of their feet (flies). But why did these arriving males stick out their tongues like tasting the air around them? Check out the video on you tube and judge for yourself.
|Tarantula Hawks, Pepsis sp.|
|Chlorion sp. Cricket Hunter|
|Cicada Killer, Sphecius convallis|
|Velvet Ant, Timulla sp|
|unidentified Eumeninae (Potter and Mason Wasps)|
|Paper Wasp, Polistes dorsalis|
|Three is a crowd|
The evolutionary advantage of this behavior is not clear. To me it seems that the loose aggregations maybe the more primitive version which excludes group-thermoregulation as a primary incentive. All these males are without stingers, so they can't deter predators in a group-response. Actually, they are so passive, they don't even seem to profit from the increased vigilance of a multitude of eyes. Alcock concludes that the aggregation may result in a dilution of risk for the individual, but one could argue that such an accumulation of rather sluggish prey could also draw predators? If I can learn how to find the wasps reliably and repeatedly, shouldn't generations of predators have figured it out as well?