December, 2006

Potter Wasp

This month's focus is on the potter wasp (Eumenes fraternus). This small, solitary wasp is in the same family (Vespidae) as the mason wasps, mud daubers, and the social paper wasps and hornets. Although adult wasps are vegetarian, and often seen feeding on flowers, their larvae require meat, usually in the form of insects or spiders. Potter wasps get their name from the little pot-like nests they construct of mud, which they provision with caterpillars before laying an egg. Because the food must remain fresh for the young wasp grub, the adult does not kill the prey, but instead paralyses it. Much of a female wasp's energy is spent on building nests for her eggs and then finding and securing prey to go inside.

The wasp pictured above was hunting among the leaves of one of our gardens when she came upon a suitable caterpillar. Although the larva was only about 3/4 of an inch long, it was quite a challenge for the diminutive wasp. She stung it repeatedly, but the caterpillar continued to grab onto sticks and leaves, making the wasp struggle to try to get the load to a high enough location for her to get airborne. Eventually, the caterpillar seemed to be immobilized, but the wasp still had to deal with all that extra weight. I watched the drama for about 15 minutes, with the wasp eventually taking more and more frequent rests while never releasing her hard-won prize. I never did see how she managed to fly with a burden that great, but when I checked back a short time later, she was nowhere in sight.