–by Dr. Raymond Cloyd
If you have spent any time outdoors lately, you may have noticed a very distinct, grotesque looking insect on trees, shrubs, or near homes. This insect is the wheel bug (Arilus cristatus), which is common, and widely-distributed throughout Kansas and the USA. Wheel bugs, also called assassin bugs, are predators that prey on insect pests. However, the nymphs and adult can inflict a painful bite when handled by humans.
Adult wheel bugs are 1.0 to 1.25 inches long, robust with long legs and antennae, and have a stout beak and large eyes on a narrow head (Figure 1).
Fig 1: Wheel Bug Adults Mating. Male is on top of Female (Auth: Raymond Cloyd, KSU)
They are dark-brown to gray and possess a wheel or crest with 8 to 12 protruding teeth-like structures (tubercles) on the thorax that looks like a cogwheel—similar to the dinosaur—Stegosaurus (Figure 2).
Fig 2: Wheel Bug Adult (Auth: Raymond Cloyd, KSU)
Wheel bugs have two long, slender antennae that are constantly moving or weaving around. Females are typically larger than males. Females lay eggs that resemble miniature brown bottles with white stoppers (Figure 3).
Fig 3: Wheel Bug Eggs on Leaf Underside (Auth: Raymond Cloyd, KSU)
The eggs are laid in clusters of 40 to 200, and are glued together and covered with gummy cement that protects eggs from weather extremes and natural enemies (e.g. parasitoids and predators). The egg clusters are located on leaves, or the trunk or branches of trees or shrubs. The nymphs hatch (eclose) from eggs and are bright red in color with black markings. The nymphs do not have the wheel or crest. The life cycle, from egg to adult, can take 3 to 4 months to complete. Wheel bugs are active day and night, and are very shy, tending to hide on the underside of leaves. The wheel bug has one generation per year and overwinters as eggs.
Wheel bugs are voracious predators feeding on a wide-variety of insects, including caterpillars (Figure 4)
Fig 4: Wheel Bug Adult Preparing to Attach a Caterpillar (Auth: Raymond Cloyd, KSU)
beetles, true bugs, sawflies, and aphids. Unfortunately, wheel bugs will feed on beneficial insects such as ladybird beetles and honey bees. The mouthparts are red-brown in color and resemble a tube or straw that is located underneath the head. The mouthparts extend out when wheel bugs are ready to “stab” prey. Wheel bugs paralyze prey with their saliva, which contains a toxic substance that immobilizes prey within 30 seconds. In addition to feeding on insects, wheel bugs are cannibalistic, and will feed on each other…AWESOME J.