In the world of entomology, we often speak of beneficial insects as insects we’d like to preserve, such as the lady beetle, lacewing or minute pirate bug, because they prey on small, soft-bodied insect pests like aphids and spider mites. However, when someone is getting bitten, this redeeming aspect of the insect’s behavior is far from central in a person’s feelings.
One beneficial insect has become a pest to some people I’ve talked to this fall at sports outings and various outdoor activities. It is the minute pirate bug. Some may also call these insects “no-see-ums,” however this name applies to biting midges, or small biting flies. Minute pirate bugs are “true bugs” (in the insect order Hemiptera). A close relative of this insect is the insidious flower bug, Orius insidiosus.
Minute pirate bugs bother humans by occasionally biting exposed flesh. Although they can move quickly, they generally don’t fly away quickly, so one can generally find and dispatch the perpetrator in short order.
Purdue Extension’s Field Crops Pest Management Manual describes minute pirate bugs as being about 1/16 inch long and about one-fourth as wide. Other sources describe the length as 2-3 millimeters long. The bottom line – it’s small. The forepart of its wings is white with a triangular black spot just in front of the membranous black portion. To me, the most recognizable aspect of their body is what appears like a little white diamond-shaped area on their posterior end.
The Purdue manual also says that this insect is a predator found on almost any plant where other insects or insect eggs are found. Adults and nymphs, immature insects, insert their piercing-sucking mouth parts into their prey to extract the body fluids. It commonly preys on small aphids, spider mites and caterpillars, as well as on the eggs of many insects. One study referenced by Virginia Tech University estimated the prey consumption of Orius to be 30 spider mites per day. This behavior is its redeeming quality as a beneficial insect.
Back in the early 2000s, I, along with several other Extension Educators around the state, was conducting field research on soybean aphid, a new pest to Indiana at the time. One of the aspects of that weekly research was noting the presence of insect predators, including the minute pirate bug. Purdue entomologists John Obermeyer and Larry Bledsoe reported in 2002 that the minute pirate bug is one of the first predators to appear in early growing soybean plants, and is thought to keep most early invading aphids in check. I observed that predator populations tended to increase when pest populations increased, although the build-up tended to lag behind the balloon of the pest population by several days.
Although these bugs can bite humans, controlling them is not recommended since they are an important biological control agent. In fact, homeowners should try to increase the numbers of these friendly bugs in their yards. Generally, this means to refrain from pesticide use until pests like spider mites threaten the health or appearance of your plant.
John Woodmansee is an extension educator in Whitley and Noble counties.