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Paper wasps are good caterpillar predators

Posted: March 11, 2012 - 12:06am

Gardeners are always on the lookout for a new product that will make gardening easier, or for a new plant for the landscape.

I am always on the lookout for better ways of controlling insects without using many pesticides, so I try to encourage as many beneficial insects as possible in my garden.

One beneficial insect is the paper wasp, which is a predator of caterpillars.

Most of us have an unpleasant memory of being stung, or we have a fearful reaction when we encounter a nest of paper wasps (Polistes sp.) under the porch or carport ceiling. The first thing we reach for is the broom or spray can of insecticide.

Paper wasps should not be confused with their relatives, dirt daubers, which are dark metallic blue, build mud-tube nests, catch spiders, and do not sting people unless caught in the hand. Paper wasps, in contrast, often sting when disturbed on their nest.

Paper wasps build nests of open, gray, paper-like cells that are attached to the underside of a support and hang downward. Mated females overwinter in dry protected areas, such as hollow trees, under bark, in woodpiles, open barns, attics or wall voids. In the springtime when the weather warms, these females (queens) search for a place to build a nest. It is always in a place with some protection and overhead cover.

The overwintered female starts to build the nest by chewing dead wood and mixing it with saliva to form a few cells that hang from a short stalk. She lays an egg in each cell and guards the nest. She feeds the young larvae pieces of chewed caterpillar.

Just like us, insects need protein. Honey bees get their protein from pollen. Wasps obtain protein by eating other insects. Hornets, for example, feed upon flies and other flying insects. Paper wasps generally eat caterpillars.

Some of the common pest caterpillars that paper wasps feed on are cabbage butterfly and several oakworm species. Some paper wasps colonies have been reported to kill as many as 2,000 caterpillars. Thus, wasps can be real biological control for the landscape and garden.

Wasps are helpful in the landscape, and paper wasps are one of the easiest to manage. All that needs to be done is to provide nesting sites. The key is to encourage the wasps to build nests where they will be out of the way and not a hazard.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net, or at (706) 836-2152.

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