Ensign Wasp: The Cockroach Controller


Growing up, I was told by my housekeeper that this insect was the mosquito king. Literally today, I finally know that it is actually an ensign wasp and it is harmless. Ensign wasps are actually helpful because they help control the cockroach population in your house. This is why you can just leave them alone if you see one as they are not dangerous to humans. There are a few things to know about them so let’s have a look below.


This unique-looking wasp is very small, growing to only around 5 to 7 millimeters long. It has a broad head, a stout thorax, 3 pairs of legs, and 2 pairs of wings. Ensign wasps are black in color, and the first thing that you will see is the abdomen. An ensign wasp has a very small metasoma that is very high above its hind coxae with a long on-segmented petiole. The petiole is the narrow waist of the insect, and it resembles a tube. If you used to see one, then you definitely notice the bug jerk its metasoma up and down. It does so when it is active, and its antennae are very beneficial in locating prey. And of course, it has an ovipositor to inject its eggs into the host, and its ovipositor is short and thin.


A female ensign wasp lays their eggs inside the cockroach ootheca (egg case), and the eggs become the meals for the larvae. It takes from 15 to 30 minutes for a female to penetrate the tough integument of the egg case and insert her ovipositor. One egg is laid per single ootheca and the larva hatches very quickly, and it consumes the eggs of the host. The freaky part is that sometimes ensign wasps oviposit the female cockroach that still carries the fresh ootheca around. But normally, they will only attack the ootheca that are completed and have been dropped by the female cockroach.

Is it possible for two ensign wasps to lay their eggs in the same ootheca? Yes and no, some can determine if an ootheca is already a host to another wasp. However, if there are two eggs in one egg case, the one that hatches first will eat both eggs. The larvae of the ensign wasps can be cannibalistic in this case.

As a wasp, does it sting humans? No, it does not bite or sting at all so there is nothing to worry about. Be happy that you see one around because they help to control the population of roaches in your home.

3Feeding & Habitats

The larvae of ensign wasps are parasitoids so they feed on cockroaches as they develop inside the egg cases. Adult ensign wasps are usually outdoors so they feed on flowers and honeydew, with a lifespan of 2-3 weeks. As solitary wasps, they hang and hunt alone using their antennae to locate prey. The habitats of these insects are both indoors and outdoors as long as there are cockroach eggs for them. It can be anywhere in the house or outside such as forest floors, palm bracts, piles of wood, tree holes, etc.

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