Warning, this is not geology related (though it does mention a cairn) but I think it’s pretty cool natural history nonetheless. Yesterday, I spent 40 minutes watching a nifty little episode involving a wasp and a spider. It started when I noticed a caterpillar on a concrete block retaining wall in our backyard. When I got closer to the wall, my eyes were drawn to a metallic blue flash six inches below the caterpillar. The flash came from the wings of a black, half-inch long wasp, which had a firm hold on a brown spider with a body about the size of a lentil.
The wasp was pulling the spider up the wall. After topping the wall the wasp and the spider dropped into the soil and duff inches behind the blocks. The wasp began to tug the spider over twigs, needles, and small rocks for about four inches, when it let go and started crawling around with short flights. Twenty seconds or so later it found what it was looking for, an entrance to what looked like an underground chamber, into which the wasp disappeared.
After the wasp emerged it flew directly to the spider. It landed, grabbed the arachnid’s abdomen, and began to pull it toward the hole. Not deviating from its route, the spider climbed over fir cones and through low vegetation, eventually letting go of the spider three inches from the opening. It then headed to the hole and began to excavate like a dog, using its legs to shuffle soil out of the way. Next it entered the hole, where I could not see what it was doing, though periodically it would back out, toting a small stone, some as much as a third as long as the wasp.
I am pretty sure that I had been watching a Pompilid wasp. This group of often large and colorful wasps is known for its macabre egg-laying lifestyle, Pompilid wasps, also known as spider wasps and tarantula hawks, fly around till they find a spider, sting and paralyze it, then drag it to an underground chamber where they lay an egg in the still-living spider. When the egg hatches it has a ready-to-eat meal. Pretty cool.
Okay, I admit that I piled up the wee rocks to make the cairn, sort of a low level publicity stunt for my new book, but I like to think that the wasp would have made a cairn if it could.