I watched part of a neat little drama in my Longmont, Colorado back yard yesterday. While I didn't see the opening act, my attention was drawn to movement on a flagstone pathway underfoot. Stooping over, I saw a small black wasp dragging a spider along backwards. I spooked the wasp and it flew away, but when I backed off it returned to claim its trophy and continue to drag it along the pathway.
I ran inside to get my camera, and by the time I got back outdoors it took me a while to re-find the wasp & hapless spider- the wasp was making quick progress. It was hard to snap pics because it moved so fast, and when I got in too close the wasp would drop the spider and run or fly off. Luckily, it kept coming back to its victem, and eventually it dragged it up and over a low retaining wall.
It left the spider along the wall and began enlarging a burrow in the sandy substrate under my flagstone patio. I had noticed these burrows and sandy spoil piles near my grill but didn't know what was doing the digging. Well, now I know. I looked into the situation and I think I found an apt description of these wasps here: http://www.museums.org.za/bio/spiderweb/predator.htm
Belonging to the family Pompilidae, these spider-hunting wasps immobilize their prey with a sting, drag them to their burrow, and lay an egg in the spider. The hatched larva consumes the spider and then pupates in a protective cocoon to wait out the winter. Vicious world, isn't it?
If anyone knows more about these wasps (in general, or this specific one) I'd love to hear from you.
I also made a little video that shows the digging behavior and the spider transport & burial. Somehow I decided to add a little soundtrack and narrative, too- procrastinating more serious work, I guess. Enjoy-