Small spiders are one of the most common enemies who can be found in all the newly added floors in the expansion, especially in the Cellar. They move very quickly and will go in all directions randomly, making them unpredictable. However if they have a direct line of sight on the player and are close enough, they will move towards the player's position. Finally, due to their small size, they can even fit between the corners of some rocks. As such, it's best to stay as far from them as possible.
Like most other monsters, spiders will deal 1/2 heart damage on touch on most levels and a full heart of damage from Utero onwards. Their health is as low as of Gapers and Horfs, dying after 3 hits from Strength 2 tears, although landing a shot is quite difficult because of their small size and fast movement speed.
Besides simply appearing on the level, spiders are also be spawned when fighting Sacks, Widow, The Husk. The Wretched, Super Sloth (2 at once) and when destroying smallest part of the Teratoma (also 2 at once). Outside of combat, two spiders can occasionally come out of the opened Red Chest and they will always be spawned if you destroy a Devil Beggar.
If killed by a spider, no picture will appear on the Isaac's Last Will. It is unknown whether this is a mistake or intentional.
Female Spiders look like regular spiders with a large black thorax attached. They behave in the same way as the regular spiders, having the same movement speed and also dealing 1/2 heart of touch damage. However, they have almost double the health of regular spiders, and on death, they will split into two small spiders. This can be avoided if they're killed in a single hit from attacks like Ipecac or Sacred Heart tears.
Trites are even larger spiders with a upside down face. It possesses large fangs and four eyes that are leaking blood. They are functionally identical to the flaming Hoppers, randomly jumping great distances around the room, although they will move towards the player if they're too close.
Trites deal 1/2 heart of damage on touch, but only after they have landed; it is entirely possible to move safely beneath them while they're airborne. They can still receive damage from tears while in the air, though, although it's best to target them just after they landed, because they will wait about 1.5 seconds before the next jump. Trites will die after six hits with Strength 2 tears like F. Hoppers.
They are commonly found in the Cellar and Catacombs, and rarely in Necropolis. Some Hoppers are sometimes replaced with these during Challenge Room fights or Greed encounters. They're also spawned by The Wretched during her boss fight.
If the player gets killed by a Trite, the summary will state that it was a hopper instead. This hints the Trite has the same coding as a flaming hopper.
- All spiders only have 4 legs. Edmund has acknowledged this by saying he doesn't know how spiders work. http://www.formspring.me/EdmundM/q/347549200755476067
- A Trite's Face resembles Isaac's appearance when upgraded with Mutant Spider.
- The name Trite was first used by a monster from the Doom franchise.
- Both Wrath of the Lamb's and Doom's Trite are inspired by a monster of John Carpenter' "The Thing". This was confirmed by Edmund on formspring. (Link needed)
- Spiders don't have a "passive" variant like flies do (the black fly).