Hardy Fruits Specialist Kathy Wiederholt discovered something interesting in her research plots last week. It was the nest of a potter wasp on a currant twig (see top photo).

Curious Kathy cracked open the nest and discovered it contained a wasp larva (shown by arrow) and several "dead" caterpillars. Cool! After she shared this finding, we needed to learn more about this nest. We discovered the potter wasp, one of the coolest insecticides in North Dakota:

Potter wasps are not aggressive. They’ll sting you if you handle them, but who wants to handle a wasp?

Potter wasps feed on flower nectar; not people. They are pollinators; they are our friends.

Potter wasps are solitary insects. They do not develop scary colonies like hornets or yellowjackets.

Now comes the cool stuff: After mating, a female potter wasp constructs nests to lay eggs. She goes back and forth carrying drops of mud to build the nests (see bottom photo). When completed, the nests looks like clay pots hand thrown on a potter’s wheel; thus the name “potter” wasp.

After making a nest she fills it with caterpillars, typically 1–12 caterpillars. She hunts down each caterpillar and then stings it with just enough venom to paralyze it, but not kill it. She then carries the caterpillar and drops it into nest. This hunting can take several days. Some of the literature reports the mother knows how many caterpillars to put in the nest: five or fewer for a male egg; more for a female.

Finally, she will lay the egg into the nest, suspending it at the top. She closes the nest with mud and flies away to prepare another nest.

The egg will hatch and then feed on the paralyzed caterpillars. After eating for a couple weeks it pupates. Later it will burrow out of the nest as an adult wasp. Emerging females will mate and destroy dozens of caterpillars for their eggs.

This potter wasp is harmless to us, but can help control caterpillar pests. It is a natural insecticide!

Every time we see a bug on a plant, we don’t need to freak out. We don’t need to spray it with poison. The vast majority of the insects in our yard are neutral or beneficial to us. Insecticide sprays can be very useful, but we need to use them judiciously. We don’t want to be harming potter wasps, ladybugs or other beneficial insects.

In addition to killing caterpillars, potter wasps can be valuable as pollinators. A Canadian scientist recently reported they are experimenting with pruning old raspberry canes down to five inches instead of the normal practice of pruning to the ground. The stubs would be used as sites for nest building by potter wasps. Such strategies are used where the lack of bee pollination is reducing yields. I am not sure I agree with this—a clean orchard is important to prevent pests and diseases—but this is interesting nonetheless.

The bottom line: Nature is cool!

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Published in the NDSU Yard & Garden Report, August 4, 2014. Photos were made available under Creative Commons licenses specified by the photographers: Kathy Wiederholt, NDSU; and Natasha Mhatre.

Sources:

Grissell, E.E. 2013. Potter wasps of Florida. Univ. of Florida: Gainesville.

Wikipedia. 2014. Potter wasp. Accessed online 7/31/2014, en.wikipedia.org/wiki/Potter_wasp.