Latrodectus

Walckenaer, 1805

widow spiders, black widow spiders, brown widow spiders

Species Guides

Latrodectus bishopi(Red Widow)
Latrodectus geometricus(Brown Widow)
Latrodectus hesperus(Western black widow)
Latrodectus mactans(Southern Black Widow)
Latrodectus variolus(Northern Black Widow)

Latrodectus is a of cobweb spiders (Theridiidae) containing approximately 34-35 distributed worldwide except Antarctica. Females are typically dark-colored with distinctive reddish abdominal markings, often hourglass-shaped, while males and juveniles frequently display red or red-and-white patterns. The genus is medically significant due to potent venom containing the latrotoxin, which causes the condition latrodectism. Despite their reputation, bites rarely cause death in humans. The "widow spiders" derives from observations of sexual , though this is more common in laboratory settings than in nature.

Latrodectus hesperus by (c) Luke Padon, some rights reserved (CC BY), uploaded by Luke Padon. Used under a CC-BY license.

Latrodectus variolus by (c) Samuel Paul Galick, some rights reserved (CC BY), uploaded by Samuel Paul Galick. Used under a CC-BY license.

Latrodectus variolus by (c) Annika Lindqvist, some rights reserved (CC BY), uploaded by Annika Lindqvist. Used under a CC-BY license.

Pronunciation

How to pronounce Latrodectus: /ˌlætrəˈdɛktəs/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Females distinguished by dark brown to shiny black coloration with red or orange hourglass marking on surface; some show paired red spots or lack markings entirely. Males typically smaller with red or red-and-white abdominal markings ranging from single stripes to bars or spots. Juveniles generally resemble male coloration patterns. Body length 3–13 mm for females, with leg span reaching 25–38 mm. Comb-like rows of bristles on hind (comb-footed spiders) visible under magnification. sacs of some species (particularly L. geometricus) characterized by white silk spikes on exterior.

Images

Habitat

Constructs irregular, tangled, sticky webs in dark, undisturbed, protected locations. Outdoor nests typically near ground level in small animal burrows, construction openings, woodpiles, under logs, stones, or boards. Indoor include basements, sheds, garages, beneath furniture or desks, and cluttered storage areas. Frequently hangs inverted near web center.

Distribution

Found on every continent except Antarctica. North American include L. mactans (southeastern United States), L. hesperus (western North America), L. variolus (northern United States and southern Canada), L. geometricus (pantropical, established in southern United States), and L. bishopi (Florida). Other notable species: L. hasseltii (Australia, New Zealand), L. tredecimguttatus (Europe, Mediterranean), L. katipo (New Zealand), and multiple button spider species in southern Africa.

Diet

Prey consists of small insects including flies, mosquitoes, grasshoppers, beetles, and caterpillars. Feeding involves envenomation and silk-wrapping of trapped prey, followed by external digestion through pulsed digestive juices and capillary ingestion of liquefied material.

Life Cycle

Females produce multiple sacs annually, each containing hundreds of spiderlings. Eggs hatch in 14–21 days. Spiderlings may remain in egg sac from several days to one month before . Newly emerged spiderlings typically white and unpatterned, developing coloration and markings through subsequent .

Behavior

Constructs irregular, tangled cobwebs rather than geometric orb webs. Hunts by waiting inverted in web center, detecting prey through vibrational cues rather than vision. When threatened, typically escapes by dropping on silk safety line or plays dead; bites occur primarily when escape is impossible. Males assess female feeding status through chemical cues in silk to avoid post-mating . Sexual cannibalism documented but primarily observed in confined laboratory conditions; natural occurrence associated with male inability to escape rather than female predatory intent. Some exhibit opportunistic cannibalism including sibling cannibalism under stressed conditions.

Ecological Role

of small insects in terrestrial . Prey for predators including the blue mud dauber Chalybion californicum in western North America. Silk exhibits tensile strength comparable to steel wire of equivalent thickness.

Human Relevance

Medically significant venomous bites causing latrodectism, characterized by severe muscle pain, abdominal cramps, diaphoresis, tachycardia, and muscle spasms. typically persist 3–7 days but may extend to several weeks. Approximately 2,500 bites reported annually in the United States; most require no medical treatment. No deaths reported in the United States since 1983. Antivenom available but primarily used for pain management rather than life-saving intervention. Bites generally defensive, occurring when spiders are accidentally squeezed or pinched. Prevention involves wearing gloves in potential areas and reducing clutter in storage spaces. Frequently introduced to new regions through human commerce, with established in greenhouses and similar protected environments outside native ranges.

Similar Taxa

SteatodaAlso Theridiidae with similar body shape and dark coloration; known as "false widow spiders" but significantly less harmful to humans; lacks distinctive hourglass marking of Latrodectus females.

Misconceptions

Sexual is not inevitable; males often escape unharmed after mating, particularly when females are not hungry and males can depart freely. The "black widow" is taxonomically imprecise as the includes brown, red, and other color morphs. Bites are rarely fatal despite genus notoriety. Spiders are not aggressive and bite only defensively.