Black Recluse

Black Recluses are hardmode enemies that spawn in Spider Nests, but can rarely be found in the Cavern layer. It can inflict the Venom debuff and itself is immune to the Poisoned and Venom debuffs.

Farming
If you can find a large enough Spider Nests you can make a hole in the top and use a piercing weapon, such as the Poison Staff to take advantage of their fast spawn rate. Poison Staffs sell for about 4 gold (and with a good reforge up to 12 gold) making a great early hardmode farming strategy that gets you souls and money. It can also be turned into an automatic farm with some traps from the Lihzard.

Trivia
The name "Black Recluse" is a combination of the spider names "black widow" and "brown recluse"; both spiders are commonly known for their venomous capabilities. This is reflected in the monster's appearance and in its drops.