Another article, another wasp – another beneficial insect

By Ralph E. Mitchell

Wasps are so amazing that I am going to continue on a roll with another beneficial wasp article. Imagine if you had a tiny automated drone programmed to find and kill cockroaches. How much would you be willing to pay for it? A small insect called the ensign wasp provides such a service at no cost! Ensign wasps are odd-shaped black wasps that not only don’t sting or bite, but are actually beneficial for a very specific reason mentioned earlier – they parasitize cockroaches! But, as the sight of any wasp can alarm people, learning more about this harmless and helpful insect may calm fearful hearts.

Ensign wasps are called ensign wasps because they have a habit of raising and lowering their small, flat abdomen just as if they were signaling with a flag. They are black in color and relatively large for this type of wasp measuring up to three-fourths of an inch in length. Ensign wasps are solitary and do not build a hive or nest. This particular species was probably introduced in ships hundreds of years ago as it followed its food source – cockroaches. Ensign wasps particularly like to parasitize the American cockroach, the Australian cockroach, the Brown cockroach and the Smoky Brown cockroach. Normally found outside, ensign wasps search in piles of wood, palms bracts and hole in trees for cockroach egg cases. Cockroaches lay an egg case, which contains multiple individual eggs – twelve for example within the American cockroach egg case. A female ensign wasp finds and locates an egg case (called an ootheca) where it inserts a single egg. The wasp egg hatches and the larvae feeds on the cockroach eggs until all are consumed. The wasp larva pupates in the egg case and then hatches out from a hole at one end of the case completing its life cycle. As adults, ensign wasps only live two to three weeks and can be found visiting flowers and feeding on honeydew.

Now when ensign wasps engage cockroach egg cases outside unseen by the homeowner, all is well. But when black, spider-like wasps begin to emerge inside a home, fear can ensue. Again, keep in mind that ensign wasps cannot bite or sting and control is not necessary. Also keep in mind that if there are no cockroaches, there will tend to be no ensign wasps either. Work to eliminate sources of food, moisture and hiding places to deter cockroaches from entering homes. While ensign wasps cannot totally eliminate a cockroach population, they are very useful in suppressing cockroaches as part of an Integrated Pest Management (IPM) program.

Be nice to ensign wasps because they are working for you,,,for free! For more information on wasps and other insects, please call our Master Gardener volunteers on the Plant Lifeline on Mondays, Wednesdays and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer. Don’t forget to visit our other County Plant Clinics in the area. Please check this link for a complete list of site locations, dates and times – .

Stange, L. A. (2018) A Cockroach Egg Parasitoid, Evania appendigaster (Linnaeus) (Hymenoptera: Evaniidae) The University of Florida Extension Service, IFAS.
Gray, B. (2006) Beneficials in the Garden – Ensign Wasp. Texas A & M University – Galveston County.


Posted: May 2, 2018

Category: Agriculture, Home Landscapes, Horticulture, Pests & Disease
Tags: Beneficial, Cockroach, Ensign Wasp, Integrated Pest Management, Wasp

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