Saturday, July 12, 2008

Beasts on the barbie: spider wasp.

Some time in July, last year, I saw a frenetic, blue-black wasp skittering around on the patio. It would run right, then left, then fly a few feet, land, and do the same again. It seemed to be looking for something. At the time I had no clue what kind of wasp it was. It disappeared, but a while later I spied it again, coming down the barbecue lid, carrying a big clue.

Spider wasp with paralyzed prey. (Image slightly out of focus to soften the horror.)

An orb-weaver, I think. Anyway, this was a spider wasp, family Pompilidae. A female will paralyze a spider, then go prepare a nest in soil amid rocks or other debris (or have a nest pre-prepared). She will then retrieve the hapless arachnid, take it to the nest and lay an egg on its abdomen. The egg will hatch, and the wasp larva eat the still-living spider.

I watched the wasp drag the spider around for a while. She went all the way down to the rack at the bottom of the grill, then climbed back up a leg and ended up next to the ignition switch.

She left the spider there and flew away, perhaps to make sure the nest was ready to go. I found it interesting that the spider was deposited in such a conspicous spot. Perhaps the whole drag-it-around-the-grill routine was an effort to find a conspicuous landmark, so that upon returning from the nest she would have no difficulty finding the spider.

I went inside for a while and when I returned, the spider was gone. I never saw the wasp again.

Unidentified spider wasp, Family Pompilidae.

1 comment:

Northern Shade said...

Insect adaptations are fascinating, from the beautiful to the grisly. The drama did make me glad that I'm a couple of metres taller than the wasp, and 6 legs short of being a brooding ground.