ARTHROPOD MUSEUM NOTES
Number 11 2002 • revised May 20, 2003 • Jeffrey K. Barnes
Brown recluse and Mediterranean recluse spiders
Genus and species: Loxosceles reclusa G & M and L. rufescens G & M
The brown recluse spider, Loxosceles reclusa, is variable in color, but usually a dark and dull grayish brown or yellowish brown. Individuals can reach about 3/8” long, excluding the legs. They have 6 eyes arranged in 3 pairs, rather than the 8 eyes found in most spiders. A distinctive violin-shaped dark marking is present on the cephalothorax of this and other recluse spiders. Consequently, species in the genus Loxosceles are often referred to as violin spiders or fiddleback spiders (Gertsch and Ennik 1983).
Brown recluse spiders occur in the central and southeastern United States, but because of its habit of taking up refuge in homes and its ability to survive long periods without food or water, it is possible that they are being transported long distances. Arkansas is at the center of the species’ natural distribution, and this spider is common in both urban and rural settings. Opportunities for contact with it abound. Indoors, the spiders are often found in boxes, among papers, in folds of clothing, and in bedrooms, bathrooms, cellars, and attics (Hite et al. 1966). They tend to prefer dry locations that remain undisturbed, such as closets, attics, and garages. Outdoors, the spiders are found under rocks, logs, or loose bark in relatively dry areas, such as under rock ledges.
The Mediterranean recluse, Loxosceles rufescens, also has been found in Arkansas. It originated in the Mediterranean region of North Africa and Europe, but it is now widely distributed in temperate and tropical areas. It was introduced into the United States and is now established mainly in buildings in several eastern and Gulf states. It is distinguished from the brown recluse by its distinctive genitalia, and also by the arrangement of the eyes, with the anterior eyes separated from the laterals by 1 1/2 to 2 diameters rather than the 1 diameter or less separation found in the spiders of the reclusa group. Although it has not been studied as thoroughly as the brown recluse, it should be regarded as venomous and dangerous.
Brown recluse spiders are commonly active at night, when they hunt for insect prey. Because of their nocturnal habits, they are rarely seen. They will feed on many kinds of arthropods. Individuals can live for two years or more, surviving long periods of up to 6 months or more without food or water. The spider builds an irregular, medium sized web of sticky silk, and often constructs a retreat of loose silk somewhere in the web. Webs are not particularly important for prey capture, and the species is an active hunter. Winter retreats outdoors are tubes of thick silk. Females each produce up to five egg sacs and 300 eggs (Horner and Stewart 1967).
Since the latter half of the nineteenth century physicians in South America have recognized the peculiar sloughing skin lesions that are now known as necrotic arachnidism or loxoscelism. North American physicians began seeing ever increasing numbers of similar lesions in Arkansas, Kansas, and Missouri in the mid 1950s (Dillaha et al. 1963). These were first associated with brown recluse spider bites in 1957 (Atkins et al. 1957). Until that time, black widows were regarded as the only spiders from the United States that could inflict bites serious enough to warrant medical treatment. Several species of Loxosceles are now known to be venomous, including both the brown and Mediterranean recluse. Probably all members of the genus are dangerous to some degree. Brown recluse spiders are regarded by some as potentially more dangerous than the black widows because it cohabitates with humans and its appearance is quite innocuous.
Recluse spiders are not aggressive and bite only when forced into intimate contact with human skin. Bites often occur when spiders are trapped in clothing or bedding. Both males and females can bite and deliver venom. Human reactions to bites can vary from minor temporary irritation to severe systemic conditions that occasionally result in death. Typically, bites go unnoticed for several hours, but they can also be intensely painful almost immediately. They can eventually result in a circular red area on the skin, which sloughs off, leaving a slow-healing, open wound and exposed muscle tissue. The edges of the wound become thickened and raised, while the central area is filled by dense scar tissue. Lesions can range in diameter up to 10 inches. Healing can take up to two months or more. The victim is often left with a sunken scar that looks as if a hole had been scooped from the body. In some cases, the victim also suffers a general systemic reaction. Symptoms can include fever, rash, nausea, vomiting, hemolytic anemia, bloody urine, renal failure, and shock (Hufford 1977).
First aid for someone who has been bitten by a brown recluse spider includes use of an ice pack to prevent or to reduce the swelling in the area where the bite occurred. Cooling the area helps to lessen tissue damage. Also, sanitizing the area with hydrogen peroxide or alcohol helps to prevent infection. Promptly seek medical attention. If the spider can be found, it should be collected and taken with the patient to the doctor to confirm the identity of the spider involved. The bite of a brown recluse is certainly a serious condition and hospitalization of the victim may be required. Those in poor general physical condition, young children, and older people are more apt to be affected seriously by the bite of the brown recluse.
Familiarization with the habits and appearance of brown recluse spiders can help reduce the chance of being bitten. Removal of stored boxes, loose brick, wood, trash, clothing, and other disused items will eliminate many favored hiding places. Caulking or otherwise tightening foundations helps prevent the entry of spiders into buildings. Stored clothing and shoes should be shaken out before being worn. In heavily infested homes, carefully check and shake out bedding before going to sleep. Bed skirts should also be removed to reduce the chances of spiders crawling onto the bed. Remove any spiders found by vacuuming. Dispose of the bag contents outdoors. Perform regular inspections for spider infestations. Remove webs so that potential spider activity can be monitored in future inspections. The person conducting the inspection should wear gloves. To prevent spiders from crawling up pant legs, constrict the pants with rubber bands around the ankles. The person may even consider wearing a bee veil when inspecting severely infested buildings to prevent spiders from dropping on them. Sticky boards placed along walls can also be used for monitoring purposes. Be cautious when cleaning storage areas. Places suspected of harboring brown recluse spiders may be treated with insecticides. Reducing insects around infested areas is an important factor in spider control as the insects serve as a food source for the spiders. Use of pesticides labeled for spider control is warranted for serious brown recluse infestations. Spot treating corners or cracks and crevices in a house with a pyrethroid pesticide, and treating crawl spaces with a dust formulation are some techniques available. Enlisting the services of a professional pest control operator is an option to be seriously considered for brown recluse infestations. Professional pest control services can use flushing agents as a monitoring tool in an effort to locate breeding areas.
Atkins, J. A., C. W. Wingo, and W. A. Sodeman. 1957. Probable cause of necrotic spider bite in the Midwest. Science 26 (3263): 73.
Dillaha, C. J., G. T. Jansen, W. M. Honeycutt, and C. R. Hayden. 1963. The gangrenous bite of the brown recluse spider in Arkansas. Journal of the Arkansas Medical Society 60 (3): 91-94.
Gertsch, W. J., and F. Ennik. 1983. The spider genus Loxosceles in North America, Central America, and the West Indies (Araneae, Loxoscelidae). Bulletin of the American Museum of Natural History 175: 264-360.
Hite, J. M., W. J. Gladney, J. L. Lancaster Jr, and W. H. Whitcomb. 1966. Biology of the brown recluse spider. University of Arkansas (Fayetteville) Agricultural Experiment Station Bulletin 711: 26 pages.
Horner, N. V., and K. W. Stewart. 1967. Life history of the brown spider, Loxosceeles reclusa Gertsch and Mulaik. Texas Journal of Science 19 (4): 333-347.
Hufford, D. C. 1977. The brown recluse spider and necrotic arachnidism: a current review. Journal of the Arkansas Medical Society 74 (3): 126-129.
• Brown recluse bites - University of Nebraska-Lincoln