Adult female black widow spiders are usually black and shiny. Black widows are most commonly recognized because of the reddish hourglass shape on the underside of the abdomen. Females measure an average of 3.5 cm in length, and typically have a very round abdomen.
Adult males are half the size of females. Their bodies are smaller, but they have longer legs than the females. Males have yellow and red bands and spots dorsally.
Newly hatched black widows are white, but can sometimes be a yellowish-white. As they get older, they slowly turn black. Mature black widows can vary in the amounts of red and white on their bodies.
Average mass: 25 g.
Average length: female, 3.5 cm; males, 1.25 cm.
Other Physical Features: ectothermic ; bilateral symmetry ; poisonous
Sexual Dimorphism: female larger; sexes colored or patterned differently