Focus on Stinging Insects: Arachnids with the Fiery Tail

Scorpions are eight-legged arthro-pods with a stinger at the tip of their tail. Taxonomically, they are placed in the order Scorpiones under the class Arachnida. There are about 1,400 species occurring on all major land masses except Antarctica. Some species are more dangerous than others, depending upon the type of venom.

STING REACTIONS. Interestingly, size does not determine how dangerous a scorpion is. For example, scorpions in the genera Pandinus and Heterometrus (Old World) and Hadrurus (New World) are huge, ugly and menacing, but are no serious health hazard. Stings from most species (Centruroides vittatus is a common offender in the United States) are like that of bees and wasps. There is immediate sharp pain at the site of venom injection and often moderate local swelling (which may be discolored). Dr. Scott Stockwell at the Walter Reed Biosystematics Unit compares the sting to hitting your thumb with a hammer. Regional lymph node enlargement, local itching, tingling sensations, fever and occasionally nausea and vomiting may also occur. Signs and symptoms in a person stung by a scorpion with this type of venom usually subside in a few hours; however, a person with insect sting allergies could have an allergic reaction from this type of venom.

The more deadly scorpion species are in the family Buthidae and have a neurologic venom. Clinical effects from stings of many of these scorpions include drowsiness, abdominal cramps, blurred vision, spreading partial paralysis, muscle twitching, abnormal eye movements, profuse salivation, perspiration, high blood pressure, rapid heart rate and convulsions. Extreme restlessness is frequent in children. In fact, very young children may flail, writhe and display roving eye movements. Death is probably the result of respiratory paralysis and/or heart complications and may occur at any interval between 1½ to 42 hours.

There was one fairly recent report in the medical literature where four cases of scorpion stings in the southwestern U.S. by our only dangerous species, C. exilicauda (formerly called C. sculpturatus), caused severe clinical manifestations, including respiratory failure, metabolic acidosis and severe multiorgan system disease. Other than the sting of C. exilicauda in Arizona and surrounding areas, scorpion stings in the United States are not usually life-threatening (barring allergic reaction), but scorpions constitute a severe problem in other areas of the world, such as northern Africa and Central and South America. For example, the number of scorpion stings in Morocco — many with life-threatening results — is estimated to be 40,000 per year.

SCORPION CHARACTERISTICS. Scorpions look sort of like crabs or lobsters, with pincers attached to their two front appendages. Their five-segmented "tail" terminates in a bulbous structure with a prominent curved stinger. Adult scorpions vary in size from 2 to 10 cm, depending upon the species. Most American species are yellowish-brown or brown in color. C. exilicauda, the dangerous U.S. species, is yellow to yellowish-brown in color and is relatively small (usually 6 cm maximum). It is a slender species with narrow and elongated tail segments. A variant form of C. exilicauda may also occur with two irregular black stripes down its back. At one time people thought this striped version of C. exilicauda was another species named C. gertschi.

The most commonly encountered species in the U.S. is the common striped scorpion, C. vittatus, whose sting is about as painful as a wasp or bee sting. The species is especially common in Texas and is responsible for numerous nonfatal stings each year. The only dangerous scorpion (other than via allergic reaction) in the United States, C. exilicauda, occurs primarily in Arizona, but also in southeastern California, Nevada, southern Utah and southwestern New Mexico. In Mexico, this species has been found in Baja, California at Puerto Punta Penasco, Sonora.

Female scorpions have pouches in which the young develop for a time period, before being born alive. Subsequently, they climb onto the mother’s back and remain there until molting about two weeks later. After this molt, the young scorpions scatter to live solitary lives, molting six or seven more times before reaching maturity.

Scorpions are nocturnal feeders, feeding mostly on insects and spiders, although there are reports of the larger species feeding on lizards, snakes and other small vertebrates. They seize prey with their claws and then paralyze it by their sting. During the day scorpions remain concealed and are only encountered when people disturb them. Some of the most dangerous species are called "bark scorpions" because they are often found under loose bark and in the crevices between the bases of palm tree leaves. They do not burrow but hide under boards, bricks and other rubbish. Ground scorpions, on the other hand, burrow into loose sand or gravel and are capable of hibernating without food or water for up to seven months.

Around homes, scorpions are usually found in rock piles, under bricks, under the houses themselves (crawl spaces) or in attics. They may enter attics by climbing between wall partitions. However, they will abandon attics as soon as the temperature gets too high, migrating downward into the walls and if an opening is available, into the house itself. They favor attics with air conditioning ducts that provide cool temperatures and a place to hide. Because scorpions seek water, they are often found in bathrooms, kitchens or laundry rooms at night. It is not uncommon to find them in bathtubs or sinks, for which they enter seeking water and then are unable to climb back out.

CONTROL.Perimeter treatments with residual insecticides provide effective barriers against scorpion entry into buildings. However, environmental sanitation is likely the most important and effective step in scorpion control. The Mallis Handbook of Pest Control lists the following steps for long-term scorpion management: