Spiders are Arachnids, a group that also contains mites, ticks and scorpions. They differ from insects in that they lack antennae and possess wingless bodies with two segments and four pairs of legs. In contrast, insects possess long antennae, bodies with three segments, three pairs of legs, and usually wings. Most spiders have venom to subdue their prey, but they only use it against humans if disturbed. Spiders are beneficial to humans because they feed on pest insects in homes and gardens.
The most common spiders associated with health threats in the United States are the black widow spider (Latrodectus spp.) and the brown recluse spider (Loxosceles spp.).
Adult female black widow spiders are approximately 1" long and ½" wide. They have bulbous, shiny, jet-black abdomens with reddish, hourglass-shaped marking on their undersides. Adult males are smaller with much longer legs than females. Both immature and adult males have yellow and red bands and spots over their backs. Newly hatched spiders are white to yellow-white and gradually change to black after three to six molts. Immature black widow spiders of both sexes resemble the adult male black widow.
Adult female and male brown recluse spiders are yellowish-tan to dark brown with a dark violin or fiddle-shaped marking on their backs, thus giving them the other name of 'fiddle back spiders'. Adult females are ¼-½" long and have long, delicate legs with short dark hair. Immature brown recluse spiders closely resemble the adults except for their smaller size and slightly lighter color.
Black widow females lays 300-400 eggs in a globular, white silken sac, about ½" in diameter. The sac turns pale brown in later stages of development. They may produce four to nine egg sacs during the summer. Most of the developing spiders are cannibalized during the 14-30 days of egg incubation and only 1-12 survives from each egg sac. Black widow spiders take two to four months to develop, depending on the availability of food. Females molt six to eight times and males only three to six times before becoming adults. Females mature about 21 days later than males and start to mate and lay egg sacs soon after maturation. Adult females live approximately 179 days, whereas adult males live only about 30 days. Black widow spiders often consume their mates. However, a well-fed female will not eat her mate, allowing him to mate again.
Brown recluse females lay about 300 eggs from May to August. The egg sacs are off-white, about 1/3" in diameter, and contain more than 40 eggs. The egg sacs are deposited in the web, and the mother guards them during winter. The immature spiders emerge in 24-36 days. Similar to black widow spiders, development of brown recluse spiders depends on availability of food and environmental temperature and may take from 10-12 months. These spiders generally live for two years or longer.
Black widow spiders spin their webs outdoors in secluded areas and generally live under rocks, fallen trees, woodpiles, basements, and crawlspaces . Very hot and/or cold temperatures and depleted food sources can drive them indoors to survive. Brown recluse spiders are very reclusive and prefer undisturbed, dry, dark, cluttered, and secluded locations and are found behind baseboards, under tables and/or chairs, basements, crawlspaces, attics, garages, and sheds. They also hide in unused clothing, and in undisturbed beds and shoes.
Spiders rarely bite humans. Most spider bites result from accidentally disturbing a spider in hiding or cornering a spider and preventing its retreat . Spiders such as the black widow (female only) and the brown recluse (female and male) are equipped with hollow fangs (chelicerae) that inject venom. Normally, spiders only use their chelicerae to inject venom into prey. However, if provoked, they use these fangs to bite and inject venom into whatever might be threatening them.
The black widow's venom is a neurotoxin, a toxin that affects the nervous system. The bite feels initially as if being stuck with a needle and intense pain develops very shortly afterwards. Pain may continue up to 48 hours if untreated. Other reactions to black widow venom include: fever; increased blood pressure; swelling at the bite site accompanied by two faint red spots (fang marks) and local redness; severe abdominal cramps and muscle rigidity; generalized muscle pain, pain in soles of feet, and pain and swelling of the eyelids; profuse sweating; dizziness; blurred-vision, labored breathing and speech; and nausea and vomiting.
The brown recluse's venom works differently than the black widow's venom. It is a cytotoxin, a toxin that affects the flesh and produces necrosis, or tissue death. Initially, the spider bite is not felt but it starts to sting shortly after the bite and is followed by intense pain. Occasionally, it may take more than an hour before a person reacts to the venom. Reactions to brown recluse's venom include: development of a small white blister that gradually increases in diameter as the venom attacks and kills surrounding tissue (size can range from size of a human thumbnail to the span of a human hand); breaking of blood vessels, which results in blood leaking into tissues; subsequent death of affected tissue which sloughs away and leave a sunken, ulcerated sore or "volcano lesion." The healing process may take from six to eight weeks.
If bitten by a black widow spider, contact your medical provider or poison control center, or go to the emergency room immediately. Health care professionals can administer an antitoxin, which will reverse the effects of the spider venom. If possible, bring the spider for identification. Black widow bites are rarely fatal when treated promptly. However, small children should be considered at a greater risk.
If bitten by a brown recluse spider, contact a physician, poison control center, or go to the emergency room immediately. There is no antitoxin for brown recluse's venom; however, health care professionals can provide medical treatment that may prevent further tissue death and eventual scarring. Brown recluse bites cannot be visually distinguished from the bite of any other spider. Therefore, it is important to capture the spider and bring it to the doctor for identification.
To protect against spider bites: