Thread-Waisted Wasp

Some years ago, the tree beside our mailbox became infested with yellownecked caterpillars. (I believe the following moth is the adult form of these caterpillars. Please comment if you can confirm or correct my identifications!)

That first summer, the tree’s lower branches were stripped of leaves by fall. The next summer, thread-waisted wasps arrived in the yard.

Dozens of these wasps dug burrows in the loose soil under the tree. The following year, we saw very few caterpillars and even fewer wasps. The tree kept most of its leaves. Another year later, the caterpillars surged again. More wasps, as well.

They continue on in this pattern. Every other summer, we have caterpillars and wasps, with the between years bringing decreased populations of both.

The wasps are very efficient. A burrow takes only fifteen or twenty minutes to complete. They dig with their front legs and jaws, vibrating their wings as if to loosen the soil faster, and carry the excavated dirt several feet away. Each trip clears a pea-sized lump.

When the burrow is deep enough, they fly into the tree, sting a caterpillar, and let the stunned victim fall. They find the caterpillar on the ground, grasp it in their impressive jaws, and drag it into the burrow. A few minutes for egg laying, and the job is done. (I missed this part of today’s activity because my camera batteries died. 😦  Maybe I’ll get another chance tomorrow.) When finished, the female stuffs clumps of dirt and small stones into the burrow’s entrance. Then she moves to a different part of the yard and starts all over again.

The sandy parts of our yard, where grass grows poorly, are peppered with burrows right now. Next year, I expect the tree will keep its leaves all summer.

As a final note today, this might be the same mockingbird that I photographed yesterday. It certainly had the same sneeze…