Part 4

Identification. Female velvet ants, wingless and antlike in appearance, are actually wasps that only resemble ants. The males are winged and usually larger than the females. Both male and female are covered with a velvety pubescence which is normally bright red, orange, or yellow. The female has a formidable stinger at the posterior end of her abdomen which she can use to inflict a painful envenomization. The length of a mature mutillid wasp varies from 1 to 2.5 cm (0.4-1 in). In some localities, mutillids are commonly referred to as cow killers, mule killers, or wooly ants.

Distribution. The Mutillidae is a large family with most species distributed in the southern and western parts of the United States. However, one species, Dasymutilla occidentalis, is commonly found on the sandy beaches of Lake Erie and during the summer months causes barefoot bathers much distress.

Biology/Behavior. Female velvet ants are solitary, diurnal, parasitic wasps. An efficient stinging apparatus and an extremely thick exoskeleton allow the female mutillid to conspicuously, yet safely, run about in the open searching for a suitable place to lay her eggs. Most cases of human envenomization occur when the female wasp is accidentally touched while roaming about on the ground or is trapped against the body in clothing or bedding.

Avoidance/Control. The solitary and roaming nature of velvet ants makes it very difficult to predict or designate ways to avoid contacting them. In areas like the beaches of Lake Erie where mutillids are known to frequent, however, potential victims should be made aware of the velvet ant hazard and how to avoid accidental envenomization. Since mutillids are not gregarious and do not congregate in accessible places, chemical control is not feasible.

Envenomization Reaction/Treatment. (See appendix.)

5. WASPS (Order: Hymenoptera; Family: Vespidae)

Identification. This information applies to all dangerous wasps found in the United States except the mutillids (previously discussed). Wasps are elongate insects with three distinct body parts and four wings. As with all winged forms of Hymenoptera, the front pair of wings is larger than the hind pair. Only the female wasps are equipped with a stinger at the posterior end of the abdomen. To distinguish wasps from similar-appearing bees, the specimen’s thoracic hairs should be examined microscopically to determine if they are smooth (a wasp) or feathered (a bee). In the United States, members of the paper-wasp family (Vespidae) are generally considered to be the most dangerous because of their social nesting habits, aggressive behavior, and abundance. Two representative members of the Vespidae family found in North America are the bald-faced hornet, Vespula maculata, and a common yellow jacket, V. pennsylvanica. Although it takes an expert to identify most wasps according to species, the paperlike nests of the vespids make their identification easy. Another important group of dangerous wasps easily distinguished by their nests are the mud daubers. These wasps usually build their mud nests in the corners of man-made structures. Besides their distinctive nests, mud daubers are identified by their dark shiny color and long narrow waist.

Distribution. Dangerous species of wasps can be found throughout the United States.

Biology/Behavior. Most vespids are social insects that feed primarily on other arthropods. These wasps build paperlike nests by masticating wood fiber into pulp. In addition to the social wasps, many types of solitary wasps are capable of envenomization; but these wasps are easy to avoid since they are neither abundant nor aggressive. Female members of the dangerous wasp species will readily attack and inject their venom if someone disturbs or annoys them. Wasp stingers do not become detached, and a single wasp can sting a victim several times before retreating. Social wasps are particularly dangerous because a disturbance of their nest may result in attack by numerous wasps.

Avoidance/Control. Avoid garbage accumulation sites, which attract wasps. To avoid wasp stings, recognizing the nests of the dangerous species in the local area, is important. If possible, remove and destroy all nests found around inhabited areas. Wasps can be controlled by treating their nests with insecticide—preferably at night, when the wasps are least active. Treat nests found above the ground with a commercial wasp spray or other insecticide recommended by an entomologist. To treat wasp nests in the ground or in houses, a 5% carbaryl dust may be used.

Envenomization Reaction/Treatment. (See appendix.)

URTICATING/VESICATING ARTHROPODS

1. BLISTER BEETLES (Order: Coleoptera; Family: Meloidae)

Identification. The Meloidae are narrow elongate beetles characterized by a “neck” (pronotum) which is distinctly narrower than its head or wings. Adult beetles range in body length from 1 to 2 cm (0.4-0.8 in) and vary considerably in their coloration.

Distribution. In general, blister beetles are found in greater numbers in the western half of the United States.

Biology/Behavior. The immature stages of the blister beetle are usually predacious on other insects and are not harmful to man. Adult blister beetles release a clear amber fluid by rupture of thin membranes in the leg joints or other segmented areas of the body. The release of this fluid, which contains a vesicating agent called cantharidin, is triggered by pressure against the body of the beetle. Light pressure exerted by clothing or by brushing off a beetle is usually sufficient to cause the release of its vesicating fluid. The adult blister beetles are readily attracted to bright white light, and many cases of human exposure occur at night around such lights. Since the adults are plant feeders, some cases of human vesication occur as persons move through vegetation infested with blister beetles.

Avoidance/Control. In areas with an abundance of blister beetles, use yellow light bulbs for outdoor lighting. If a meloid beetle lands on the skin, blow it off, do not crush it. Since cantharidin is distributed throughout the beetle’s body, crushing the beetle against exposed skin would result in maximum cantharidin exposure. Dermatoses resulting from blister beetle contact are seasonal, with the greatest number of vesicating incidents in the United States occurring in July, August, and September. Chemical control usually is not recommended because of the mobility and wide distribution of blister beetles.

Envenomization Reaction/Treatment. This information is not included in the appendix because the envenomization reaction generally consists of a superficial linear bulla which does not require emergency treatment.

2. URTICATING CATERPILLARS

a. IO MOTH CATERPILLAR (Automeris io)

Identification. The Automeris io caterpillar is the larva of the Io moth, which belongs to the moth family Saturniidae. A full-grown caterpillar is about 5 to 8 cm (2-3 in) long, pale green, with lateral strips of red or maroon over white running the length of the body. Near the center of each body segment is a partial row of tubercles armed with radiating green and black spines. Many of these spines are venomous, and their tips are connected to rather large individualized poison glands.

Distribution. In the United States, the Io moth is found in the states east of the Rocky Mountains.

Biology/Behavior. Io moth larvae feed on the leaves of a variety of plants, including corn and willow. In most areas they produce only one annual generation, emerging as a moth in the spring or summer and overwintering as a pupa. In south Texas, however, two generations occur, with one developing in May-July and the second in October-December. Therefore, the urticating larval stages can be found anytime from early spring to late fall, depending upon the area of the country and climatic conditions. As with most urticating caterpillars, A. io envenomizations normally occur when the victim inadvertently contacts caterpillar-infested vegetation. At the instant the victim’s skin touches this caterpillar, the spine tips break off in the skin, thus allowing toxin to flow out of the hollow spines and onto the skin.

Avoidance/Control. Wear gloves, a long-sleeved shirt, and long pants when working in an infested area. Children should be warned not to handle caterpillars. If necessary, infested vegetation may be treated with an appropriate insecticide.

Envenomization Reaction/Treatment. (See appendix.)

b. PUSS CATERPILLAR (Megalopyge opercularis)

Identification. The puss caterpillar is the larva of a lepidopterous group commonly referred to as “flannel moths.” In some parts of the United States the larva is incorrectly referred to as an “asp.” When fully mature, the larvae are near white to dark gray in color, 2 to 3 cm (0.8-1.2 in) long, and completely covered dorsolaterally with hairs that cause them to resemble elongate tufts of cotton. Some of the hairs are venomous, and when they penetrate the skin a “toxin” passes from an underlying gland through the hairs at the points of contact. The color variation of the larvae in this species is dependent upon larval age, locality, and time of year. In Texas, where this species is most abundant, the spring/summer generation of caterpillars is usually lighter in color than the fall generation.

Distribution. This species has been recorded primarily from the Southeastern States, including Alabama, Arkansas, Florida, Georgia, Louisiana, Maryland, Mississippi, Missouri, North Carolina, South Carolina, Texas, and Virginia.