Latrodectus is a genus of spider, in the family Theridiidae, which contains 32 recognized species. The black widow spider is perhaps the best-known member of the genus. The venomous bite of these spider species is considered dangerous because of the neurotoxin latrotoxin, which causes the condition latrodectism, both named for the genus. The female black widow has unusually large venom glands and her bite is particularly harmful to humans; however, Latrodectus bites rarely kill if proper medical treatment is provided.
The prevalence of sexual cannibalism, a behaviour in which the female eats the male after mating, in some species of Latrodectus has inspired the common name “widow spiders”. The female’s venom is at least three times more potent than that of the males, making a male’s self-defense bite ineffective. Research at the University of Hamburg in Germany suggests this ultimate sacrifice strategy has evolved to promote the survival odds of the offspring; however females of some species only rarely show this behavior, and much of the documented evidence for mate cannibalism has been observed in laboratory cages where the males could not escape.
Females of most Latrodectus species are dark or black in colour usually exhibiting a red or orange hourglass on the ventrum underside or bottom of the abdomen — some may have a pair of red spots or have no marking at all. They often exhibit various red or red and white markings on the dorsal or top side of the abdomen, ranging from a single stripe to bars or spots. Females of a few species are paler browner shades and some have no bright markings. Juveniles and adult male Latrodectus are half the size of the females, and are often grey or brown and usually lighter in colour than females; while they may sometimes have an hourglass marking on their ventral abdomen, it may be yellow or white, not red. Variation in specifics by species and by gender is great.
Due to the presence of latrotoxin in their venom, black widow bites are potentially dangerous and may result in systemic effects (latrodectism) including severe muscle pain, abdominal cramps, hyperhidrosis, tachycardia, and muscle spasms. Symptoms usually last for 3–7 days, but may persist for several weeks.
Outpatient care following discharge often consists of a weak-to-moderate strength opioid (e.g. codeine or tramadol, respectively) depending on pain scores, an anti-inflammatory agent (e.g. naproxen, cortisone), and an antispasmodic (e.g. cyclobenzaprine, diazepam) for a few days to a week. If the pain and/or spasms have not resolved by this time, a second medical evaluation is generally advised, and other diagnoses may be considered.