Scorpions have long been of interest to humans primarily because of their ability to give painful and sometimes life threatening stings. Scorpions are also an important and beneficial component of many ecosystems and they are one of the oldest known terrestrial arthropods. Fossil scorpions found in Paleozoic strata 430 million years old appear very similar to present day species.
Scorpions are venomous arthropods in the class Arachnida, relatives of spiders, mites, ticks, solpugids, pseudoscorpions and others. There are currently 1400 recognized species of scorpions worldwide. Scorpions have an elongated body and a segmented tail that is tipped with a venomous stinger. They have four pairs of legs and pedipalps with plier-like pincers on the end, which are used for grasping.
In the United States, scorpions are most common in southern Arizona and in a swath of land extending through central Texas and central Oklahoma. The common striped scorpion, Centruroides vittatus, reaches from northwest Mexico to southern Colorado, Kansas, southern Missouri, and Mississippi and Louisiana. Species of the genus Vaejovis are found from Florida north to Maryland, the Carolinas, and Tennessee, and as far west as Oregon and California. Paruroctonus boreus is found through the Northwest U.S. and into Canada (Southern Saskatchewan, Southern Alberta and the Okanagan Valley of British Columbia). Scorpions can be found in 31 different states in the U.S., including Hawaii (Isometrus maculatus).
Facts About Scorpions
First off, the belief that scorpions commit suicide by stinging themselves to death when surrounded by fire is of considerable antiquity and is often prevalent where these animals exist. It is nevertheless untrue since the venom has no effect on the scorpion itself, nor on any member of the same species (unless the venom is injected directly into the scorpion's nerve ganglion�quite an unlikely event outside of the laboratory). The misconception may derive from the fact that scorpions are poikilotherms (cold-blooded): when exposed to intense heat their metabolic processes malfunction. This causes the scorpion to spasm wildly and this spasming may appear as if the scorpion is stinging itself. It is also untrue that alcohol will cause scorpions to sting themselves to death.
The striped bark scorpion (Centruroides vittatus) is an extremely common scorpion found throughout the midsection of the United States and northern Mexico; indeed, it is perhaps the most frequently encountered scorpion in the U.S.
A medium-sized scorpion that is rarely longer than 60 mm(up to around 7cm), it is easily identified by two dark, longitudinal stripes on its carapace, with a dark triangular mark on its head. There are minor variations on this theme, however; specimens that are lighter-colored and lack the characteristic stripes have been described as separate species in the past.
Like many scorpions, C. vittatus is primarily a nocturnal insectivore. They are highly adaptable, and can be found almost anywhere with plenty of crevices in which to hide or hunt; these include forests, rocky areas, and buildings, where they can be a frequent indoor pest. The species does well in captivity.
Noted for their complex courtship behavior, their long breeding season runs from autumn through early summer; after an eight-month gestation, they give live birth to a brood of as many as 50 young.
Though not aggressive, the scorpion's close association with humans makes envenomation relatively common. The sting is painful, but the worst of it passes in 15-20 minutes; fatalities are rare, and due to anaphalactic shock rather than the venom itself. Reported direct deaths are controversial.
The Arizona bark scorpion (Centruroides sculpturatus, previously known as Centruroides exilicauda), is a small (7 cm) light brown scorpion common to the southwest United States. Originally described as Centruroides sculpturatus, the species was synonymized with Centruroides exilicauda by Williams in 1980.
It is venomous, although its sting is rarely lethal; exceptions are cases involving small children or people allergic to the venom. An antivenom was developed for this species, and produced in quantities sufficient to treat individuals within the state of Arizona.
The bark scorpion is unusual in that it is the only species in the southwest that regularly climbs walls, trees, and other objects with a sufficiently rough surface. It is not capable of climbing glass or smooth plastic, so it may be safely contained in glass vessels without lids. It is one of two species within the United States that is dangerous; the other, far less dangerous, species above.
Arizona bark scorpions are not true desert species; they prefer riparian areas, with sufficient moisture and humidity to support insects and other prey species. However, the popularity of irrigated lawns in residential areas has led to an explosion in the number of these animals in some areas. The availability of moisture seems important in the life cycle of the species. Females will not give live birth if kept too dry, and babies seem susceptible to drying out and dying up to the first or second instar.
Desert Hairy Scorpion Another species found in Arizona is the desert hairy scorpion (Hadrurus arizonensis). This species is twice as large as the bark scorpion at maturity (up to 5 inches long). They are often found in low sandy areas throughout the state.
Desert hairy scorpions usually eat insects, spiders, centipedes, small vertebrates and other scorpions.
Stripe Tailed Scorpion Another genus frequently found is the devil or stripe-tailed scorpion group (Vaejovis spp.). There are several Vaejovid species found in Arizona. They are intermediate in size (1-2 inches in length) and are more robust than bark scorpions.
The stripe-tailed scorpion is typically found under many surface objects (including sleeping bags, shoes, etc.) where it digs a short burrow or "scrape" for protection. This species is normally an obligate burrower, digging burrows about one meter deep in gravel soils.
As arachnids, scorpions have mouthparts called chelicerae, a pair of pedipalps, and four pairs of legs. The pincer-like pedipalps are used primarily for prey capture and defense, but are also covered with various types of sensory hairs. The body is divided into two main regions, a cephalothorax and an abdomen. The cephalothorax is covered above by a carapace (or head shield) that usually bears a pair of median eyes and 2 to 5 pairs of lateral eyes at its front corners (a few cave and litter-dwelling scorpions are completely eyeless).
The abdomen consists of 12 distinct segments, with the last five forming the metasoma what most people refer to as the "tail". At the end of the abdomen is the telson, which is a bulb-shaped structure containing the venom glands and a sharp, curved stinger to deliver venom.
On its underside, the scorpion bears a pair of unique comb-like sense organs called the pectines; these are usually larger and bear more teeth in the male and are used to sense the texture and vibration of surfaces. They also serve as chemoreceptors (chemical sensors) to detect pheromones (communication chemicals).
Scorpions are nocturnal or diurnal, predatory animals that feed on a variety of insects, spiders, centipedes, and other scorpions. The larger scorpions occasionally feed on vertebrates, such as small lizards, snakes, and mice. Prey is detected primarily by sensing vibrations with the pectine organs. The pedipalps have an array of fine sensory hairs that sense air-borne vibrations; the tips of the legs have small organs that detect vibrations in the ground. Most scorpions are ambush predators who detect prey when it comes within reach.
The surfaces of the legs, pedipalps, and body are also covered with thicker hairs (setae) that are sensitive to direct touch. Although they are equipped with venom for defense and prey acquisition, scorpions themselves fall prey to many types of creatures, such as centipedes, tarantulas, insectivorous lizards, snakes, birds (especially owls), and mammals (including shrews, grasshopper mice, and bats).
As with many predators, scorpions tend to forage in distinct and separate territories, returning to the same area each night. They may enter homes and buildings when their territory has been disrupted by construction, tree removal or floods, etc.
Scorpions have many adaptations for desert living. They have extra layers of lipids (fats) on their exoskeleton (external skeleton) that minimizes water loss. Most are active at night, and spend their days where it is cool and moist under rocks, wood, tree bark or in burrows. Although scorpions have been seen drinking directly from water reservoirs, they derive most of their water from their food (although this varies by species).
As with most arthropods their activity is linked to temperature. Generally speaking, scorpions are active if nighttime temperatures are above 70oF. They tend to be less active during winter and the hottest part of the summer during daylight hours
The venom of scorpions is used for both prey capture, defense and possibly to subdue mates. All scorpions do possess venom and can sting, but their natural tendencies are to hide and escape. Scorpions can control the venom flow, so some sting incidents are venomless or only mild envenomations. Scorpion venoms are complex mixtures of neurotoxins (toxins which affect the victim's nervous system) and other substances; each species has a unique mixture. Despite their bad reputation, only one species in the western U.S. (the bark scorpion, Centruroides exilicauda) and about 25 others worldwide have venom potent enough to be considered dangerous to humans.
The world's most dangerous scorpions live in North Africa and the Middle East (species in the genera Androctonus, Buthus, Hottentotta, Leiurus), South America (Tityus), India (Mesobuthus), and Mexico (Centruroides). In some of these areas, scorpion stings may be a significant cause of death, but reliable data on human mortality are not readily available. Some studies suggest typical mortality rates up to about 4% in hospital cases, with children and the elderly being most susceptible. Death by scorpion sting, if it occurs, is the result of heart or respiratory failure some hours after the incident. During the 1980's Mexico averaged about 800 deaths each year. However, in the past 20 years there have been no reported fatalities in the US due to scorpion stings.
Tips for controlling Scorpions
High numbers of scorpions can become a problem under some circumstances. If a reduced population is desirable several steps can be taken.
Scorpions are difficult to control with insecticides alone. Therefore, the first control strategy is to modify the area surrounding a house or structure:
- Remove all harborages such as: trash, logs, boards, stones, bricks and other objects from around the building.
- Keep grass closely mowed near the home. Prune bushes and overhanging tree branches away from the structure. Tree branches can provide a path to the roof for scorpions. Minimize low growing ground cover vegetation.
- Store garbage containers in a frame that allows them to rest above ground level.
- Never bring firewood inside the building unless it is placed directly on the fire.
- Install weather-stripping around loose fitting doors and windows.
- Plug weep holes in brick veneer with steel wool, pieces of nylon scouring pad or small squares of screen wire.
- Caulk around roof eaves, pipes and any other cracks into the building.
- Keep window screens in good repair. Make sure they fit tightly in the window frame.
- By managing the scorpion food source, you will manage the scorpion population.
Blacklighting Scorpions fluoresce or glow under ultra-violate light so they are easy to find with the aid of a black light during the night. Nighttime scorpion hunting is a lot of fun but make sure that you wear high-top boots and have long tongs if you want to capture the scorpions to move them.
Using BLB bulbs you can construct your own portable U.V. light. Homeowners wishing to construct an inexpensive blacklight should purchase a 6-volt camping lantern with a 6-inch fluorescent tube, from a camping supply store or department store. The tube can then be replaced with an ultraviolet bulb available at many lighting stores. This kind of light will show scorpions 1-2 feet from the light. The approximate cost of constructing the 6 volt blacklight will be $30. Another option is to obtain a 12 volt fluorescent fixture, such as an emergency auto lighting stick and a 12 volt rechargeable battery pack available at electronics supply stores. Replace the bulb with a 12 volt, 8 watt ultraviolet bulb from a lighting store. This is a more powerful system and will cost more to construct, but will allow nighttime viewing of scorpions from 4-5 feet away. The approximate cost of constructing the 12 volt blacklight will be $200.
Once located, collect the scorpions using long forceps or tongs and keep them in a sealable, sturdy container. As these wonderful creatures are such a benefit to our environment please consider collecting and releasing the scorpions into the natural desert rather than killing them. If collected scorpions are to be destroyed, crush the individuals then use a flyswatter or long forceps to remove the bodies. Chemical spraying during the day is largely ineffectual.
Wettable powder formulations provide better residual control for crawling pests when applying perimeter sprays.
When using pyrethroids or other insecticides labeled for scorpion control, be sure to use the highest permissible label rate.
When applying pesticides directly onto individual scorpions, apply judiciously. Apply pesticides around the foundation of the building and up to 1 foot above ground level on the exterior walls. Also apply pesticides around doors, window eaves and other potential points of entry. Follow directions on the package for dosage, mixing and application methods.
Pesticides registered October 2000 for scorpion control include the following: permethrin (Dragnet�), cyfluthrin (Tempo�), cypermethrin (Demon�), lambda-cyhalothrin (Demand CS�), deltamethrin (Suspend�). (You can find more products in our Scorpion Category.)
Other pesticides are registered for the management of scorpions but are not listed as they are under investigation in accordance with the Food Quality Protection Act (FQPA) of 1996. FQPA requires the Environmental Protection Agency (EPA) to reassess all existing pesticide tolerances considering the best available data on aggregate exposure to the pesticide, the cumulative effects from pesticides sharing a common mechanism of toxicity, exposure to children and potential as an endocrine disrupter. The organophosphate and carbamate insecticides share the ability to depress the levels of cholinesterases enzymes in the blood and nervous systems of insects, animals and humans. All of the organophosphate and carbamate insecticides are regulated currently by EPA on the basis of threshold effects.