Pest Profile: Ensign Wasp

The ensign wasp is an example of a parasitoid wasp species. A parasite is defined as an organism that lives in or on an organism of another species (its host) and benefits by deriving nutrients at the other’s expense. In the case of the ensign wasp, it is a parasite of the not-so-loveable household cockroaches, such as the American cockroach and the Australian cockroach.

These wasps are widely distributed throughout tropical and subtropical areas of the world. They are common in much of the southern U.S. and can extend as far north as New York City. This species of wasp is all black and relatively larger than other parasitic wasps. They have a very distinct body shape that makes this family of wasps easily recognizable; they have a long petiole that is attached to the top of their thorax region with the remainder of the abdomen attached and laterally compressed.

These wasps differ from other parasitoid wasps since they don’t lay their eggs on the adult host but rather target cockroach egg cases. When the ensign wasp comes across a cockroach egg case, she will line herself up parallel with the long axis of the case and begin to vibrate her antennae over it. After anywhere from 15-30 minutes and a lot of hard work, she will eventually insert her egg into the cockroach egg case. After emerging, the larvae will molt five times, and by the end of this molting period, they will have devoured all of the cockroach eggs within the case. Adults will eventually escape through a small, round, and jagged hole which cuts toward one end of the egg case. Adults can live for two to three weeks. When feeding, the adults are often attracted to flowers such as parsley and fennel and also enjoy the occasional honeydew.

Although wasps usually carry a negative association, the ensign wasp is beneficial. It is speculated that releasing these wasps could result in at least 50% control of household cockroaches in an infestation. Although they may be a death sentence for unwanted cockroaches, they will not sting people, so rest assured that they are working for you, not against you.

Kristen Stevens, BCE