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.

The Ugly American

American cockroach,
Periplaneta americana

If one were to poll pest control customers about what they thought was the most disgusting insect, there's a good chance the American cockroach would come out at top. First of all it's large and scary, it's very fast and, where it proliferates, it stinks. Add to this that the American cockroach is one of the few cockroaches that readily flies, and you've got a disgusting pest.

Since few people want to admit to having giant cockroaches in their homes, alternative names are often given to the American cockroach, waterbug and palmettobug being the two most common. One of our largest cockroaches (reaching lengths of just over two inches), they often look much larger to a surprised customer. They are often described as three or four inches long.

American cockroaches, while much longer lived and slower to reproduce than the more common German cockroach, can become quite prolific in the right environment.  While an American cockroach female only produces about 12 eggs per ootheca (egg case), compared to the German cockroach's 36, she lives much longer and produces more oothecae and potential offspring over her lifetime (an average 360 offspring vs the German cockroach's 320 offspring).  Left undisturbed, American cockroaches can build up impressive populations, as anyone who has opened an infested sewer manhole cover can attest.

Odors from the droppings and the insects
themselves can be noticeable in heavy
infestations of American cockroaches. Note
the stains from cockroach droppings on
these boxes in an infrequently used
storage area. Photo by Fudd Graham.

I guess one of the things that's always impressed me about the American cockroach is its ability to survive in places with little food.  They are relatively common in urban sewer and storm drain systems, as well as steam tunnels and basements and storage areas of institutional buildings like schools, hospitals, prisons and factories. These cockroaches are often living on the edge, nutrition-wise, making do with feeding on glues and starches associated with boxes and papers. They are opportunistic feeders and while they prefer fermenting foods, they will feed on dog food in the lab and will readily feed on various cockroach baits.

My colleague Dr. Fudd Graham, from Auburn University, was recently inspecting a courthouse with a chronic American cockroach infestation. Following his nose, his inspection led him to a storage room that hadn't been opened for over 18 months. The two tubes of  Advion cockroach bait Fudd applied were gone the next morning along with the cardboard on which the bait was applied. 

Typical of many infested areas of buildings, this room had a floor drain that, due to lack of use, was dry.  Dry floor drains are one of the most common entry points for American cockroaches to enter commercial buildings from sewage systems.  Many people, even building maintenance professionals, are unaware of the importance of periodically pouring a gallon or two of water into floor drains to fill the p-trap that is designed to block sewer gases and insects and other pests from entering buildings.  A dry p-trap allows cockroaches ready access to a utility room or food storage area in a building. Besides filling the p-trap, some companies have developed clever membrane devices that open for water flow, but close between use.  Trapguard and Sureseal are two commercial products and, while they can be expensive to install, provide a long term fix for gas and pest infiltration into storage and utility areas. 

The half-inch-long ensign wasp
(Evaniidae) is a sign of American
cockroach presence in a building.

Its important to remember that controlling American cockroaches has other benefits.  Eliminating American cockroaches helps reduce the potential food supply of rodents in a building. I'll guess that most PMPs have seen the disembodied wings and legs of American cockroaches left on sticky traps. This is often evidence of mice or rats, which are fond of snacking on live cockroaches plucked from sticky cards.  In addition, ensign wasps are a common parasite of American and smoky brown cockroach oothecae, and are often seen flying around buildings that have an American cockroach infestation.  While harmless themselves to people, the presence of these interesting insects is a sign of cockroach presence in a building.