University of Maryland Extension

Assassin Bugs: A generalist predatory bug

Assassin bugs (Family Reduviidae) are generalist predators that feed on a range of herbivorous insects. There are several species of assassin bugs that are common in ornamental systems. Assassin bug species vary in color and size but many are brightly colored with red and black, others camouflage well with plants. Their bodies are elongate, heads are narrow, and front legs are adapted for grasping prey. They all have very prominent, distinctly visible beaks (proboscis) that they hold under their body. Assassin bugs overwinter as “barrel-shaped” eggs on the trunks and branches of plants. Look for egg hatch in this area in May and June. The newly hatched nymphs are a bright yellow color and within a few hours they turn their more characteristic color of black with bright red abdomens. The nymphs will feed on the assortment of caterpillars (ex. gypsy moth, eastern tent caterpillars, cankerworms, fall webworm), along with other plant feeding insects that are active at this time. Within a month or so these bugs grow up to be adults that will eat even more insects.

These predators can have a significant impact, as nymphs and adults, on many of the plant feeding insects on your ornamental plants. Be careful if you handle these predators – they will defend themselves if they feel threatened (ex. picking them up) and their long beaks can result in what I am told is a painful bite.

Wheel bugs are one of the species of assassin bugs. This particular assassin bug gets its common name because of the spoke-bearing, wheel-like structure on its pronotum (section behind the head). They are large bugs with adults reaching 1- 1.5 inches. Wheel bug adults and immatures are generalist predators that feed on a diversity of insects such as caterpillars, planthoppers, sawfly larvae, aphids, and beetles. The wheel bug approaches its prey, quickly grabs it with its front legs, and then impales the insect with its beak. Through its beak the wheel bug injects digestive enzymes which liquefy the body tissues of the prey making it.


Feeding on Japanese Beetles
While sampling research plots at a nursery in May 2007, a research technician in my lab made some interesting observations. First, he saw Japanese beetle adults feasting on the foliage of a cherry tree and the skeletonization damage the beetles cause - not so unusual. But with further observation, there they were – several adult wheel bugs feeding on and killing the Japanese beetles – VERY exciting and somewhat unusual! Exciting because acts of predation are not commonly observed, and unusual in that there are not that many natural enemies that attack Japanese beetle adults. Most common natural enemies include birds, spiders, and a tachinid fly parasitoid.

Even Though Brown Marmorated Stink Bugs STINK, Some Predators Still Attack Them
As most of you know from personal experience brown marmorated stink bugs (BMSB) have reached high and damaging levels in many parts of Maryland. We have had multiple articles in the Weekly IPM Alert on these little critters that often put out a big stink, and the damage that they have been causing. Fortunately, there are natural enemies attacking and killing BMSBs. We (various Entomology and UME people) have been observing unusually high densities of predatory wheel bugs in the fields associated with high BMSB populations.

Author: Paula Shrewsbury, Extension Entomologist, University of Maryland, College Park

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