Garden Variety: Assassin bugs in your garden? No problem
Many Lawrence-area gardeners are taking notice of an interesting and distinctive insect this summer, which appears to have a larger population than usual. The insect is commonly known as a wheel bug or assassin bug (Arilus cristatus), and it benefits plants by feeding on plant pests.
Right now, the wheel bugs that are drawing attention are immature versions of adults (nymphs) and therefore lack the distinctive large rounded crests (wheels) for which they are named. The nymphs are light gray with red and black showing through on their backs. They are half an inch to an inch long, with slender bodies and long legs and antennae. Their rear ends stick up at an angle from their bodies. Look closely to see the proboscis, or straw-like mouthpart tucked under the insects’ heads.
Adults, which will start showing up in a few more weeks as the final molt occurs, are darker gray to dark brown, 1 to 1 1/4 inches long, and have the distinctive wheel in the middle of their back. They are reclusive and often hide under leaves.
The large population this year is nothing to worry about. Insect populations often cycle from year to year because of changing weather conditions (some years are better than others for development) and populations of their predators.
Wheel bugs are considered to be beneficial insects because they feed on insects that are common plant pests including aphids, beetles, caterpillars and others. Unfortunately they do not distinguish between caterpillars that turn into desirable butterflies and those that turn into pesky moths (such as cabbageworms).
Wheel bugs use their proboscis to stab and inject toxin into their prey. The toxin liquefies the other insects’ tissues, and the wheel bug then sucks the tissue out. They may bite humans if picked up or disturbed, but only in defense.
Although sometimes referred to as assassin bugs, they are only one species of that larger group. There are other common assassin bugs with similar body shapes and coloration that also prey on plant pests.
Assassin bugs may be confused with squash bugs and stink bugs, which are related but are plant pests. Always try to identify the species and/or confirm feeding habits before treating for garden pests, as treatment kills beneficial insects as well as the undesirable ones.
Other beneficial insects that are readily found in Kansas gardens in mid-summer are ladybird beetles, green lacewings, praying mantids, parasitoid flies and wasps, and damsel bugs.
There are several similar-looking species of ladybird beetles with various spot patterns and shades of orange to red. They all eat aphids, whiteflies, scale insects and other small insects. Their larvae, which are more voracious feeders than the beetles themselves, look like tiny, black-and-orange alligators and are often misidentified as a plant pest.
Green lacewings have slender green bodies and clear, lacy wings, as the name implies. Their larvae also look like little alligators but are light green to white in color.
Praying mantids are generally recognizable by their front legs that are lifted and held together, which looks like the insect is praying. There are multiple species that vary in size and color, but all are voracious feeders on other insects.
Parasitoid flies and wasps generally go unnoticed, but they lay their eggs in plant pest insects or plant pests’ eggs. When the eggs hatch, the larvae of the flies or wasps feed on the insect they were laid on.
Damsel bugs look like a long, slender assassin bug. They are more common in crop fields than in home gardens. They are also voracious eaters of plant pests.
— Jennifer Smith works in regulatory horticulture and has worked as a horticulturist for various government entities. She has experience in landscape design and maintenance and as an educator.