Western Black Widow Spider
( Latrodectus hesperus )


2013-0408-EB040000-ARA00645-Latrodectus_hesperus[1627h38s,F,A,wall]{MDame}-G.jpg

PHOTO COMMENT

IDENTIFICATION
Identification:Latrodectus hesperus
(Chamberlin & Ivie ,1935 )
Common Name:Western Black Widow Spider
Life Stage:(A) adult
Sex:male

PHYLOGENY

Phylum:Arthropoda
Class:Arachnida
Order:Araneae
Family:Theridiidae
Genus:Latrodectus
Taxon Code:ARA00645
ITIS/TSN:859132

LOCATION DETAILS
Location Name
Bay Point Regional Shoreline, Bay Point Regional Shoreline, Bay Point Regional Shoreline, McAvoy Road, Bay Point
County:Contra Costa County
ECI Site#:CAEB040000
Open Space Location:Bay Point Regional Shoreline

RECOGNITION
Description
Adults of both sexes have a characteristic red hourglass marking on the abdomen underside, which varies, in immature stages, from red to orange to yellow. Adult females are entirely black. Adult males and juveniles of both sexes are light brown with 3 pale, diagonal stripes on each side of the abdomen. Immatures have topsides olive or gray, with white or yellow stripes.
Body Length
Male: 7-8 mm. Females: 14-16 mm.
Similar Taxa
False Black Widow (Steatoda grossa) is commonly mistaken for WBW. The Brown Widow (L. geometricus) ranges into California, but has banded legs, and is most often brown, not black.

BIOLOGY
Food
Food includes beetles, cockroaches, flies and other insects.
Habitat
WBW spiders may be terrestrial or live above the ground. Webs are built in undisturbed areas.
Nesting Preferences
Web: Typically, a 3-dimensional, unorganized mass of sticky and very strong silk spun in a dark crevice or corner, near or above the ground.
Importance
WBW is North American's most venomous spider. Bites cause local swelling and redness, followed by 1-3 three hours of intense spasmodic pain, which travels from the bite site to the limbs, body, and the abdomen and back. Severe bites cause abdominal pain that lasts 48 hours or longer. Other symptoms include nausea and profuse perspiration. The elderly and young children run a higher risk of severe reactions. Untreated, tremors, convulsions and unconsciousness may result. Death from bites are extremely rare.
Range
WBW is successful in the warmer western regions of the Bay Area. It ranges from southwestern Canada, the Pacific Coast to Texas, and east into Oklahoma and Kansas.
Development
Mature males wander in search of a female. At a female's web the male spins a very small web and places a drop of sperm in the silk. The sperm package is transferred to the female genital opening. Mated females lay about 750 eggs in 4 to 9 egg sacs. Egg sacs are 1 cm in diameter, white to tan and are hung in the web. Spiderlings hatch in about 14 days. Only 1 to 12 of the cannibalistic spiderlings live 30 days. About 3 weeks after hatching, the survivors balloon. Most overwinter as immatures and reach adulthood in the Spring. Males mature in 2-5 months and die 1-2 months later; females mature in 3-8 months and live 1 to 1.5 years.

CREDITS
Photographer
Mike Dame
Insect Sciences Museum of California

References
ITIS.


.