RETURN TO BENEFICIALS HOME PAGE

 
 

Scroll Over Images and Click to Enlarge

 

 

FIGURE 1. Wheel Bugs (Arilus cristatus) are named for the prominent spiny ridge or "wheel" on the thorax.

   
 

 

FIGURE 2. Adult Wheel Bugs are dark and robust with a grayish-black or brownish-black body. They have membranous wings and long front legs that extend in jerky motions.

   
 

 

FIGURE 3. Immature stages are known as nymphs. Note the pronounced upper-bowing of the abdomen, lack of the "wheel" structure and excellent camouflage of the nymph pictured above.

   
 

 

FIGURE 4. After each of its five molts, a nymph leaves behind its outer skin layer (exoskeleton). Nymphs exit their old exoskeleton through a small opening on the thorax.

   

Quick Facts

Common Name:

Wheel Bug

Genus / Species:

Arilus cristatus

Size: ¾" long

Type of Beneficial:

Insect predator

Type of Metamorphosis:

Immature stages similar in appearance to the adult stage (i.e., simple metamorphosis)

Beneficial Stage(s):

Both adults and immatures (known as nymphs) are predators

Prey:

Caterpillars, beetle larvae and adults, aphids, other soft-bodied insects

Occurrence:

Overall populations are low but occur throughout Galveston-Houston area. Typically solitary.

Mounted Specimen?

Yes (mounted specimen for viewing available in insect collection at County Extension Office)

 

Arilus cristatus or Wheel Bugs are true bugs and in the Hemiptera order, Reduviidae family, which includes such varying insects as stink bugs, water striders and bed bugs. Although the generic term "bug" is used for all sorts of insects, scientifically it is only accurate when applied to a true bug. For example, lightning bugs, ladybugs and June bugs are actually beetles.

Wheel Bugs are one of the largest true bugs in existence reaching a length of up to ½ inches. Wheel Bugs are named for the prominent spiny ridge or "wheel" on the thorax. This semicircular crest is behind the head and bears 8 to 12 protruding teeth-like structures. This is the only insect species (both males and females have them) in the United States with such a crest. It is not known if this has a specific function, but some suggest it may alert potential predators that these slow-moving insects taste as bad as they smell.

Which leads us to the Wheel Bug’s odor. Their smell isn't as potent as their cousins, the stink bug, but the scent is strong enough to make an impression on a potential predator, even humans. When disturbed, the Wheel Bug extrudes a pair of bright, orange-red scent sacs from its anus, giving off a pungent stench.

Wheel Bugs are seen from Rhode Island to Texas. There are four (4) recognized species of Arilus, but only A. cristatus is found in the United States, though many people have never seen them. Wheel Bugs are camouflaged and very shy, hiding whenever possible. They move and fly slowly. During flight, Wheel Bugs have been compared to an ultra-light plane or large grasshopper as they produce a loud buzzing sound.

Once you see a Wheel Bug, you won’t forget it. Not only is the Wheel Bug the largest member of assassin bugs, their bizarre appearance will likely take you back. Adult Wheel Bugs are dark and robust with a grayish-black or brownish-black body. They have membranous wings and long front legs that extend in jerky motions.

The head of the Wheel Bug is very narrow with a stout, rigid, 3-segmented beak and large, multiple eyes serving the bug well as it looks for its prey. Wheel Bugs possess two long, slender jointed antennae that constantly move, waving around slowly, testing the air.

Females lay between 40-200 tiny, brown, bottle-shaped eggs in a cluster on a small shrub or tree twig. Egg masses resemble honeycombs. (At this point, the female dies, for the Wheel Bug has only one generation per year.) These eggs  overwinter, cemented together by a gummy substance that may protect them from foul weather, parasites and predators.

Each fertile egg hatches the following spring into 1/8 inch long wingless red and black nymphs with long legs. They disperse onto surrounding trees and shrubs hunting for prey—aphids and caterpillars are particular favorites. Homeowners may see these nymphs on various trees or landscape shrubs. Nymphs undergo five molts and metamorphose into an adult by summer's end.

Wheel Bugs are voracious predators, preying upon a wide variety of soft-bodied insects, “ambushing them with the accuracy of an assassin.” They are a valuable predator in forests and shade trees because Wheel Bugs dine on the hairy caterpillars that are defoliators.

When a Wheel Bug encounters its prey, it slowly lunges forward using its enlarged front legs to seize and hold its victims. Next, the Wheel Bug plunges its hypodermic-like beak into some soft body part. The Wheel Bug’s saliva contains an enzyme-laden, paralytic substance that immobilizes the prey within 30 seconds, dissolving their insides, and proceeds to drain all of the prey’s bodily fluids. End of pesky prey.

Because of the Wheel Bug’s appearance, it may seem a dangerous insect. Wheel Bugs are not aggressive and will avoid contact at all costs. However, if handled, the Wheel Bug can inflict a painful bite (technically, Wheel Bugs and other types of assassin bugs do not “bite”—pierce is a more accurate term since they have needle-like sucking/piercing mouthparts). Their “bite” has been described as a “sensation lasting several minutes” or “ten times worse than a hornet sting.” The site may take weeks or months to heal.

Regardless, when in the garden or orchard, one should always wear long-sleeved shirts and hats when working. If a bug lands on you, brush it off gently. If you are bitten, cleanse the area with soap and water and some relief may be obtained by using lotions containing menthol, phenol or camphor.

Because most of their prey are considered harmful insects, Wheel Bugs are considered beneficial insects in the garden and wooded areas, as they reduce the numbers of some troublesome insects. Wheel Bugs should be considered one of many valuable allies.

Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.

 

This web site is maintained by Master Gardener Laura Bellmore, under the direction of William M. Johnson, Ph.D., County Extension Agent-Horticulture & Master Gardener Program Coordinator.

All digital photographs are the property of  the Galveston County Master Gardener Association, Inc. (GCMGA) © 2002-2006 GCMGA - All Rights Reserved.