Department of Environment and Conservation
Did Someone Say Scorpions?
By Patricia Dobbe
If you ask a Tennessean about a scorpion sighting, the answers usually range from just a frown to "I think youre in the wrong state."
The mere mention of the word "scorpion" is enough to invoke fear and bring to mind scenes of a dry, hot climate encompassed by mounds of sand and rock with little crab-like creatures running around at night with stingers ready to strike.
Most Tennesseans never imagined that one of natures best-kept secrets is lurking just under a stone or scurrying amid the forest litter.
Two species of scorpions reside in Tennessee, the Plain Eastern Stripeless Scorpion (Vaejovis carolinianus) and the Striped Scorpion (Centruroides vittatus).
The Plain Eastern Stripeless Scorpion is the only known native to our state. The other species, the Striped Scorpion, was accidentally introduced to Tennessee.
Contrary to popular belief scorpions are not insects. Instead, they are closely related to spiders and belong to the same class, Arachnida. At some point in the past, a common ancestry is shared. They also have similar traits. Scorpions are distinguished by a compact head called a "cephalothorax," a broad segmented abdomen and a tail-like structure called a "telson." The tail tip is enlarged and contains a venomous stinger used for self-defense or to subdue overactive prey. Scorpions can control the amount of venom injected. Venom is injected by thrusting the tail forward over the head and into the prey. The venom of scorpions found in Tennessee is similar to that of a honey bee sting. The severity of the reaction is dependent upon the sensitivity of that individuals body to the venom.
Scorpions are nocturnal hunters feeding at night and hiding during the day. They are most active at temperatures greater than 77 degrees and become sluggish in cold weather. Scorpions are cold blooded, which means they are the same temperature as their surrounding environment. They can also survive long periods of time without food. During the summer months, scorpions usually feed about once a week depending on food availability. They eat crickets, cockroaches, ants, beetles, mealworms, spiders, and butterflies, just to name a few things.
Scorpions have two eyes in the center of the head and two to five extra eyes located along the front sides. These eyes are poorly developed and unable to focus sharply, thus they are useless in detecting prey and enemies. Instead, the scorpion depends on long hairs located on the surface of large pincers called "pedipalps" and a pair of comblike sense organs called "pectines" which are located on the underside of the abdomen. These sense organs are used for detection of low frequency vibrations. Scorpions usually wait for their food to come to them and then ambush it. They use their large pincers to hold and crush the prey.
Another set of smaller jaw-like pincers called "chelicerae" located at the front of the head is used to continue mashing and chewing the food. The digestive enzymes are secreted directly onto the prey from glands located underneath the abdomen while the chewing is taking place. Once the food has been sufficiently digested, it is then sucked into a food canal. Eating is a very slow process and may take anywhere from 10 to 24 hours depending on the type of prey eaten.
The Plain Eastern Stripeless Scorpion is reddish to dusty-brown in color and lacks a tooth located at the base of the stinger. This species occurs naturally in the southeastern part of the United States and is considered to be a "weak burrower" which means that it prefers areas where there are spaces or crevices which require little digging. The Plain Eastern Stripeless Scorpions occur in a variety of moist forest habitats with much understory. They like to hide under rocks, leaves and the bark of dead trees, especially pine. Winter habitat is not much different, just more protected.
The female and male scorpions live in separate places and only come together for a very short period of time to mate. During mating, the courtship resembles a dance. The male leads by grabbing the pincers of the female and moves her over a small capsule that contains the sperm which is called a "spermatophore." The female will then pick up the spermatophore. Adult females are found under and among the rocks and beneath dead standing trees. Males and immature scorpions inhabit leaf litter and live under the bark of dead trees. Birth occurs in deep crevices and cavities under rocks or in decayed logs or stumps. These scorpions usually mature in June and mating occurs in late summer (August). The gestation period is one year and litters may contain as many as 40 young.
All scorpions are "viviparous," which means that after fertilization, the egg develops inside the mother and the young are born alive. They are white and resemble adult scorpions. The Plain Eastern Stripeless Scorpion usually gives birth in late summer or early fall. After birth, the young climb onto the back of their mother where they stay for about a week before shedding the outer layer. This is called molting. They will then remain on her back for another five to seven days before becoming independent of their mother. It takes three years to mature. During this period, males will typically molt five times before becoming sexually mature and females will molt six to seven times. Scorpions do not molt after maturity. This species typically lives seven to eight years. The average body length for this scorpion is one to two inches in adults. Males are usually more slender and have a longer tail.
The Striped Scorpion is yellow-brown in color with two dark longitudinal stripes on the back of the abdomen and a tooth called a "tubercle," which is located at the base of the stinger. This species is not as long-lived as the Plain Eastern Stripeless Scorpion. It matures in approximately 12 to 24 months and may live another two years depending on the climate. Scorpions mature faster in warmer weather. Average body length is two to three inches in adults. Mating occurs in early summer and the gestation period is between six to 12 months with litters containing up to 50 young. The Striped Scorpion normally occurs in the south-central to southwestern part of the United States and into northern Mexico. In Tennessee, this species is usually found in groups under rocks and in crevices on well-drained hillsides. Clustering, or staying in groups, is common among this species.
Scorpions are collected at night using a portable blacklight also called a UV light. Exposure to a blacklight at night will cause scorpions to fluoresce green and thus are easy to see. The fluorescence is caused by a substance excreted from the outer or cuticle layer of skin. Scorpions that have just molted do not fluoresce until the new cuticle has hardened. This feature is common to all scorpions.
Scorpion sightings are very likely to increase with more and more natural habitat being consumed by development. If you should be lucky enough to encounter one, remember that they are very beneficial in controlling the insect population. Natural predators include birds, frogs, centipedes, spiders, lizards and snakes. Scorpions are very discreet creatures of the night and would prefer to stay hidden. Consider yourself very fortunate should you happen to see one of these fascinating creatures of the night.
For more information about scorpions, contact your local county agricultural extension service agent or call the University of Tennessees Plant Pest Diagnostic Center in Nashville at 615-832-6802.
(Patricia Dobbe is a biologist in the Tennessee Department of Health, Environmental Laboratory Service, Aquatic Biology Section in Nashville.)
Updated May 1, 1999; Send comments to Department of Environment and Conservation.