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Wheel Bug

Arilus cristatus


The wheel bug, in the family Reduviidae, is one of the largest terrestrial true bugs in North America, being up to 1.5 inches, or 38 mm, in length. A characteristic structure is the wheel-shaped pronotal armor. It is a moderately common, widely distributed, beneficial assassin bug that preys on man's pest insects. However, its bite usually is more severe than a bee sting, and both nymphs and adults should be avoided or handled with caution. Distribution The wheel bug occurs throughout Florida. It has been reported from Rhode Island westward through Iowa and Nebraska to California, and southward to Texas and Florida. Blatchley (1926) included Mexico and Guatemala in its range. Wygodzinsky (1949) recognized four species of Arilus in this New World genus, but only cristatus occurs in the United States. Description and Identification Adult: The wheel bug adult usually measures from 1 to 1.25 inches long. This assassin bug is a dark robust, grotesque creature having long legs and antennae, stout beak, large eyes on a slim head, and a prominent thoracic, semicircular crest suggesting a cogwheel or chicken's comb. This is the only insect species in the United States with such a crest. The number of teeth (tubercles) in the crest varies from eight to 12. Females are longer and wider than males, with the abdominal margins being more widely exposed in the females. A very fine yellowish pubescence is present over most of the body, except the elytral membrane which produces bronze-colored reflections. The overall color is mostly dark brown. Variable amounts of tiny white patches or granules are scattered throughout the pubescence. Notes on Behavior Todd (1937) reported the wheel bug under natural conditions as being very vicious in the nymphal and adult stages of development. This viciousness was not so pronounced in individuals under observation in cages. He noted that specimens collected in the field become accustomed to being handled in a very short time. The wheel bug has been reported as cannibalistic, usually based on caged specimens. Nymphs have preyed upon nymphs, and Barber (1920) reported females killing and feeding upon the males soon after copulation was complete. The wheel bug is diurnal but it has been found at lights, apparently attracted to the prey coming to the lights. Froeschner (1944) counted 76 wheel bugs at one time at lights in front of a store in southern Missouri. Sounds: The wheel bug and most other reduviids produce "chirping" sounds by rubbing the tip of the rostrum back and forth over transverse ridges on a longitudinal groove on the prosternum. Moore (1961) concluded that more evidence is necessary to establish the functions of these sounds. Scent sacs: Garman (1916) and Froeschner (1944) noted that wheel bugs, when captured, extrude (with little provocation) a pair of bright, orange-red scent sacs near the apex of the venter. These sacs give off a pungent scent. Attractant: Metzger (1928) reported that wheel bugs were strongly attracted to turpentine oil. Importance as a Predator The wheel bug has been reported preying upon a wide variety of insects in several orders including Lepidoptera, especially Arctiidae and Noctuidae; Coleoptera, especially Chrysomelidae and Coccinellidae; Hemiptera, especially Pentatomidae; Hymenoptera, especially sawflies; and Homoptera, especially aphids upon which young nymphs feed. Unfortunately, the above groups include the beneficial lady beetles and honey bees. nymph feeding Wheel bug saliva contains a toxic, paralytic substance that immobilizes and kills its victims usually within 15 to 30 sec after injection. Immatures of the locust leafminer, Xenochalepus dorsalis (Thunberg), are killed and fed upon while still imbedded in leaf tissue. Arilus cristatus is an especially valuable predator in forest and shade trees because it preys on the well-protected hairy caterpillars that are defoliators. Medical Importance When disturbed, the wheel bug can inflict a painful bite. The bite has been described variously as worse than stings from bees, wasps, or hornets. Barber (1919) and Hall (1924) described in detail the effects of such bites. In general, initial pain often is followed by numbness for several days. The afflicted area often becomes reddened and hot to the touch, but later may become white and hardened at the puncture area. Occasionally, a hard core may slough off, leaving a small hole at the puncture site. Healing time varies but usually takes two weeks and may take half a year. Smith et al. (1958) reviewed the literature concerning wheel bug bites and concluded that serious or prolonged effects from these bites usually are due to secondary infection or an individual hypersensitivity. First aid and home treatment: Readio (1927) quoted Townend Glover's report that repeated applications of ammonia water were helpful in relieving pain from the bite. Smith et al. (1958) reported that application of magnesium sulfate soaks was recommended.

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Spotted by

West Virginia, USA

Spotted on Oct 14, 2012
Submitted on Oct 15, 2012

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