Brown Recluse

brown-recluse

The brown recluse or fiddle back/violin spider (Loxosceles reclusa) gets its common name from its coloration and reclusive habits and the dark violin/fiddle-shaped marking on its top. While several species of brown recluse spiders occur pretty much throughout the southern half of United States, L. reclusa is exceedingly common in the Kansas City area.

Adult brown recluse spiders in the Kansas City area are usually about 1/-4-1/2'' long (with legs spread out in typical walking fashion, somewhat larger than a 25 cent coin). Their color is tan to dark brown with a darker fiddle-shaped marking on the top of the mid-section of the body. This spider has 6 eyes arranged in 3 groups of 2. The young are very similar to adults except for being smaller and slightly paler.

Biology

This discussion is based on L. reclusa found in the Kansas City area. The female deposits 40-50 eggs in a silken egg sac which is off-white, with the outer covering loosely woven. The sac has been described as either flat beneath and convex above (5/8'' in diameter and 1/8'' high) or as round (1/4'' in diameter). From 1 to 5 sacs are produced, each one containing 31-300 eggs. The eggs hatch in 25-39 days and the spiderlings undergo at least 1 molt within the sac before emerging. The spiderlings typically go through 8 molts, and the development period (egg to adult) ranges 266 to 444 days. Indoors, males live an average of 543 days, and females live 628 days, but 4-5 years is not uncommon. The female spins an irregular web in undisturbed areas. The web is not used to ensnare prey, but mostly as a retreat for the spider.

Both male and female brown recluse spiders can inject venom, and must be considered dangerous to humans. Injection of their venom may produce necrosis or dead tissue, resulting in an ulcerating type of sore. The bite is usually not felt, but it may produce an immediate stinging sensation followed by intense pain or this reaction may be delayed for 6-8 hours. A small blister usually appears and the surrounding bite area becomes swollen. Other symptoms may include restlessness, fever, and difficulty in sleeping. The affected tissue may gradually slough away during the next 10-14 days, leaving an open, necrotic ulcer. There is considerable discussion about this in the medical community and numerous cases have later been determined to be the result of bacterial infection, rather than of the venom. An antitoxin is being developed but it is NOT yet available.

If bitten, see a physician or go to an emergency room immediately, and take the spider along for identification purposes. It should be noted that not all brown recluse bites result in ulcer formation and that bites of other arthropods may cause similar reactions in people.

Habits

Outside, brown recluse spiders are typically found around rocks, piles of inner tubes, utility boxes, wood piles, under bark, etc. These spiders have been found in such places as inside rodent bait stations and infesting cedar shake roofs. Inside the home, they can be found in almost any undisturbed area to which they can gain access. They are most commonly found in boxes, among papers, and in seldom-used clothing and shoes, although they can be found in corners, underneath tables, behind baseboards and mouldings. Hence, storage areas such as closets, bedrooms, attics, crawl spaces, and basements are the areas of greatest occurrence. They typically run for cover when disturbed. Bites have been reported to occur when putting on seldom-used clothing or shoes, when cleaning out storage areas, or by rolling on the spider while in bed. In commercial buildings, the usual places to find brown recluses spiders include heat tunnels, boiler rooms, attics, basements, store rooms, and garages.