9. Yellow Sac Spider
The Yellow Sac Spider, with a body length from 3 to 15 mm, may be small, but it packs a punch. Common across the Americas and often found indoors, its venom is a cytotoxin that causes redness, swelling, and sometimes serious tissue damage.
Female spiders can be aggressive when protecting their eggs, increasing the chance of bites. Despite its size, this spider’s venom makes it a serious concern.