1. An arachnid belonging to the order Araneae, class Arachnida, phylum Arthropoda. The body is divided into the cephalothorax and the abdomen joined by a narrow waist. A spider usually possesses four pairs of legs as well as poison fangs. It often possesses spinnerets.
2. Anything resembling a spider in appearance.

arterial spider

SEE: spider nevus

Australian redbacked spider

A venemous spider (Latrodectus hasselti) indigenous to Australia with an extremely painful bite. The adult female has a spherical black body with a red stripe on the upper side of her abdomen and an hourglass-shaped red/orange streak on the underside. Antivenins are available.

black widow spider

The female of Latrodectus mactans. It is native to the southern U.S., but it has been reported throughout the country. It prefers to live in woodpiles and other locations where it is well hidden. It is glossy black with a brilliant red spot, usually shaped like an hourglass or two triangles, on the undersurface of the abdomen (Southern black widow), or a row of red, white, or yellow spots down the middle of the abdomen with two crosswise bars (Northern black widow). Its body measures about 1 cm (0.4 in) and its leg spread can reach 5 cm (2 in).

The incidence of black widow spider poisoning is not precisely known, but it is low.

The bite of a black widow spider initially produces a sensation resembling the prick of a pin and may be mistaken for a flea bite. A numbing pain usually lasts for a short time and then subsides. Later, the patient's abdominal muscles become rigid, and he or she becomes severely diaphoretic. Within a half hour severe abdominal cramps begin. The venom, which is neurotoxic, causes an ascending motor paralysis. Because of the severity of abdominal pain caused by the bite, the patient may be suspected of having an acute abdomen.

Black widow spider bites are recognizable by the clinical appearance of the patient and the presence of fang marks, usually very small and subtle, in the middle of an area of surrounding swelling, redness, or necrosis of the skin.

Symptomatic treatments include intravenous, intramuscular, or oral muscle relaxants, antihistamines, and benzodiazepines. Tetanus prophylaxis should be administered. Specific antivenins may be used when envenomation has severe neurological consequences.

Severe cases, esp. in children, can result in death; however, healthy adults usually respond to treatment, and most victims recover completely.

Intravenous access should be established to administer fluids, antiemetics, and/or analgesics. Stimulant drugs should not be given to patients who have been bitten by a black widow spider. Local suction is of little value because the toxin is rapidly absorbed.

Descriptive text is not available for this imageRespiratory status must be carefully monitored when morphine or a benzodiazepine is used.

Antivenin generally is used only for very young or older patients experiencing respiratory distress or when severe pain and muscle spasms are not controlled by other measures. Before the administration of antivenin, a skin test is performed to assess for allergic reaction to the horse serum used in making the antivenin. Even if the test is negative, resuscitative medications and equipment should be readily at hand to manage an anaphylactic reaction to the antivenin. In addition to the risk of acute hypersensitivity, delayed serum sickness can occur 7 to 12 days after antivenin administration.

brown recluse spider

A 3/8-in (10 mm) long spider (Loxosceles reclusa) native to North America. The bite of this spider is toxic and causes loxoscelism, which can be lethal.
SEE: Loxosceles; SEE: loxoscelism; SEE: Sicariidae

hobo spider

A 5-in (45 mm) long brown spider (Tegenaria agrestis) with gray markings introduced into northwestern North America from Western Europe. Males are more venomous than females. A bite causes erythema, blisters, subsequent necrosis of the skin, and sometimes severe, persistent headaches. Systemic corticosteroid therapy may be helpful. Aplastic anemia, intractable diarrhea, or vomiting may occur and, although rare, may be fatal.

white-tail spider

SEE: Lamponidae