Wheel Bug Vol. 9, No. 18
Arilus cristatus
Order: Hemiptera
Family: Reduviidae
This big, strange-looking bug can give a very painful bite if mishandled, but it will not go out of its way to do so. Wheel bugs belong to a large group of true bugs known as assassin bugs. Most assassin bugs are predators of other insects, which they catch and eat using piercing/sucking mouthparts. Wheel bugs are our largest species of assassin bug, with adults reaching up to 1.25 inches in body length. They are one of the top predators of the insect world.
Wheel bugs hunt by stalking their prey and using their raptorial forelegs to catch and hold it while they inject it with toxic saliva that quickly immobilizes the prey. The saliva also contains strong digestive enzymes that predigest and liquify the body contents, allowing them to be easily sucked through the needle-like stylets.
As with other true bugs, including those that are plant feeders, the stylets of wheel bugs are more than simple straws. They are more like a double-barreled syringe, with one channel for injecting saliva into the prey and another channel for sucking food into the stomach. These thin stylets are what penetrate the prey, but they are surrounded and protected by other structures that form the proboscis, a bit like a sword in a scabbard.
These big bugs are generalist predators that feed on a wide variety insects. Caterpillars are easy pickings, but they will also catch honey bees; lady beetles; mid-sized beetles, such as Japanese beetles; and even fellow bugs, such as adult squash bugs. It is sometimes possible to watch the body of a large caterpillar shrivel up as a wheel bug is feeding on it. Although wheel bugs are usually considered beneficial, their varied diet and the fact that they are never numerous keeps them from having any significant impact on pest insect populations.
Wheel bugs get their name from that large cogwheel-shaped structure on their back. This makes them easy to identify but serves no special purpose. Nymphs do not have this “wheel” and look much like the nymphs of many plant-feeding bugs, such as Acanthocephela terminalis and other leaffooted bugs.
Female wheel bugs possess a pair of bright red anal glands, which may be everted from the rear when they are disturbed. These are relatively small, but their color makes them obvious when everted. This purpose of these glands is not well-understood, but they may play a role in attracting a mate or protecting the eggs from potential predators. Like many other true bugs, wheel bugs also have other odor-producing glands that are used for defense and/or aggregation or sexual attraction.
Wheel bugs are sometimes confused with eastern bloodsucking conenose bugs, which are also in the assassin bug family. However, wheel bugs are strictly insect feeders, while conenoses feed on the blood of mammals, such as racoons and possums.
This leads to an interesting observation on insect diets. Wheel bugs are in the family Reduviidae and feed strictly on insects. Conenose bugs are also reduviids, but feed strictly on blood. Leaffooted bugs, such as A. terminalis, are in the family Coreidae, and are plant feeders. All three are “true bugs,’ belonging to the order Hemiptera, and all three have similar mouthparts, but they have very different diets.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
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