Flag waving for Americans

I never get tired of reminding PMPs that professionalism starts with good identification skills. One insect that is just rare enough to puzzle most pest control technicians is the ensign wasp.  It is also one of the odder insects found in homes and businesses.

The ensign wasp, Evania appendigaster may be one of the
oddest  looking insects in pest control. Its name comes from
the flag-shaped abdomen that it waves while searching
for its cockroach prey.

The ensign wasp is a quick and nervous little insect.  Black and 5-7 mm long, it is usually found one at a time. Though it might look intimidating with its quick actions and an abdomen bobbing up and down, it does not sting or bite.  It is, in fact, a beneficial parasite that helps control at least three household cockroaches, the American cockroach being the most common.

Ensign wasps are cockroach egg parasites. They are experts at locating cockroach egg cases (oothecae).  According to one account, when the female ensign wasp encounters a cockroach egg case, she first taps it with her antennae, presumably to confirm that it is an acceptable host for her egg.  Then she lies down beside it (I have never heard of an insect voluntarily lying on its side before!) and braces her legs against the ootheca.  After much labor she inserts her slender ovipositor into the tough ootheca and lays a single egg.  After hatching, the wasp larva matures while feeding on the dozen or more cockroach eggs inside each ootheca.  No cockroaches will hatch from an egg case that has been parasitized by an ensign wasp.

The name ensign wasp comes from the unique, stalked abdomen.  Shaped like a sailor's signal flag, the wasp frequently waves her abdomen up and down while stalking her prey as if to say, "Here I am!  Look out cockroaches!"

The oothecae of  American cockroaches are glued in out of
the way locations in walls, attics and other places. A single
egg inserted by an ensign wasp inside the ootheca will prevent
hatching.  Bugwood photo by Gary Alpert, Harvard Univ.

So what does it mean finding an ensign wasp in an account?  It means cockroaches are around. Not just any cockroaches, but one of the larger species of cockroaches (American, Smoky brown, or Oriental cockroaches).  I see one or two of these wasps in my office building every year.  I know they come from the rarely seen population of American cockroaches lurking in the walls and ceilings of our office building--something found in nearly every commercial building.  I like to think that we don't see a lot of cockroaches because we have these little wasps keeping watch.

Nevertheless if you or your customer are seeing these wasps on a regular basis, it might mean there are more cockroaches around than you suspect. Check the crawl space, attic and utility areas.  Make sure that p-traps in the floor drains are being filled with water on a regular basis.  Consider setting out sticky traps and baiting suspected harborage areas such as garages, attics, pantries or utility rooms.

If you are looking for more information to provide your customers about cockroach control, check out the Extension fact sheet Cockroaches and Their Control.