widow spider (genus Latrodectus)
Refers to spiders of the genus Latrodectus, such as the black widow. The name literally means 'widow spider'.
Widow spiders are known for having venom.
We hardly ever see widow spiders around here.
Specifically the black widow spider (Latrodectus mactans), while ごけぐも is the broader genus.
From 後家 (ごけ, 'widow') + 蜘蛛 (くも, 'spider'), referring to the female spider's tendency to eat the male after mating. The exact historical derivation is uncertain.