INTRODUCTION
The brown recluse or fiddleback/violin spider gets its common names from its
coloration and reclusive habits, or the dark violin/fiddle-shaped marking on the top of
the cephalothorax. Members of the genus Loxosceles occur in southern Europe,
temperate Africa, and in North, Central, and South America. Brown recluse spiders occur
pretty much throughout the United States and of 1 1 species recognized, 7 are of public
health importance. Recognition of the brown recluse species group is sufficient for PCO
purposes.
RECOGNITION
Adults usually about 1/4-1/2" (6-12 mm) in body length (L. laeta about
1 "/25 mm). Color tan to dark brown with a darker fiddle-shaped marking on dorsum
or top of cephalothorax whose neck points towards abdomen. Uniquely, with 6 eyes
arranged in 3 groups of 2 (diads) in a semicircle. lmrnatures very similar to adults
except for being smaller and slightly paler.
SIMILAR GROUPS
All other spiders lack a darker fiddle-shaped marking on the top of cephalothorax
and 6 eyes arranged in 3 groups of 2.
REPRESENTATIVE SPECIES
Because several species are involved and species separation is primarily by
differences in male genitalia, species identification should be left to experts. Those of
public health importance are:
- Loxosceles arizonica Gersch & Mulaik which occurs in Arizona.
- Loxosceles deserta (Gersch) which occurs in the southwest.
- Loxosceles devia Gertsch and Mulaik which occurs in southern Texas.
- Loxosceles laeta (Nicolet) which has been found in Massachusetts and occurs in
southern California.
- Loxosceles reclusa Gertsch and Mulaik, the brown recluse, which occurs in the
eastern United States.
- Loxosceles rufescens (Dufour) which occurs sporadically from New York to Illinois
and throughout the southeastern states.
- Loxosceles unicolor Keyserling which occurs in Arizona, New Mexico, and western
Texas.
BIOLOGY
This discussion is based on L. reclusa. 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"/17 mm in diameter and
1/8"/3.7 mm high) or as round (1/4"/6 mm in diameter). From 1 to 5 sacs are
produced, each 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 instars, and the development period (egg to adult) averages 336 days (range
266-444). 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 bits 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. Symptoms include restlessness, fever, and difficulty in sleeping. The
killed tissue gradually sloughs away during the next 10-14 days, leaving an open ulcer and
possibly exposing the underlying muscles and/or bone. Healing is very slow and usually
takes several weeks, resulting in dense scar tissue. In severe cases, plastic surgery may
be required. An antitoxin has been developed but it is NOT available. Call a physician or
go to an emergency room immediately if bitten, 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, woodpiles, under bark, etc. These spiders have been found in such
places as outside 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 and chairs, or in crevices such as those found along
baseboards, doors, and window moldings. 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 recluse
spiders include heat tunnels, boiler rooms, attics, basements, storerooms, and garages.
