Friday, July 6, 2012

Know Thine Enemy

"Know thine enemy"
---Sun Tzu, The Art of War

I have been fighting red wasps for years over the ownership of our deck overlooking Bull Creek.  This year their numbers were down but they developed anger management issues, stinging me twice.  This was without provocation unless you count walking out the front door.  In addition to attacking the problem again, I decided it was time to get to know my enemy better.

First I needed to identify it.  I knew from last year's experience that it was a paper wasp of the genus Polistes.  Searching images for Polistes I found this picture of Polistes metricus, a perfect match for the thorax markings except the abdomen is usually dark.  It turned out that this specimen was a color variant as others had the typical dark abdomen.

Like other paper wasps of the Polistes genus, in nature P. Metricus hangs its paper nest from branches but they have learned that buildings provide a convenient opportunity, especially openings in roof soffit, the underside of the roof overhangs.  They build their nests out of old wood fibers glued together to make an umbrella-like structure with individual cells for their eggs. 

Sterile worker wasps can be found on flowers, especially goldenrod.  They collect caterpillars, flies and beetle larvae for the egg chambers before sealing it up, feeding the larvae until they emerge as adults.  They also build and maintain the nest and protect it from invaders and external sources of danger.

Polistes nest with newborns
Only the female can sting as the stinger is a modified ovipositor (egg laying structure) not present on males.  They are not naturally aggressive but will defend the nest and that is where we come come in conflict. In spite of years of caulking, they still manage to find a way into our eaves.  Once they set up their home, sealing the openings simply causes them to escape into the house.

Caught early in a bluebird house, knocking off the nest with a stick discourages them and they frequently don't come back.  Once established in the eaves, the queen has to be killed before the colony can be eliminated.  We have been having success by using a homemade gizmo made from a plastic detergent bottle and tubing to blow Sevin insecticide powder into all the openings.  The wasps track it back to the nest and eventually it reaches the queen (we hope).

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