Monstrous Spider, Tiny (CR 1/4)

Tiny Vermin
Alignment: Always Neutral
Initiative: +3 (Dex); Senses: darkvision 60 ft., tremorsense 60 ft., and Spot +4*

AC: 15 (+2 size, +3 Dex), touch 15, flat-footed 12
Hit Dice: 1/2d8 (2 hp)
Fort +2, Ref +3, Will +0
Speed: 20 ft., climb 10 ft.
Space: 2 1/2 ft./0 ft.
Base Attack +0; Grapple -12
Attack: Bite +4 melee
Full Attack: Bite +5 melee
Damage: Bite 1d3-4 and poison
Special Attacks/Actions: Poison, web
Abilities: Str 3, Dex 17, Con 10, Int -, Wis 10, Cha 2
Special Qualities: Vermin
Feats: Weapon Finesse (bite)
Skills: Climb +11, Hide +15*, Jump -4*, and Spot +4*
Advancement: -
Climate/Terrain: Temperate forest
Organization: Colony (8-16)
Treasure: None

Source: Monster Manual

All monstrous spiders are aggressive predators.

Monstrous spiders come in two general types; hunters and web-spinners. Hunters rove about, while web spinners usually attempt to trap prey. Hunting spiders are speedier than their web-spinning counterparts and use higher speed numbers shown in parentheses.

Monstrous spiders of both types have roughly circular bodies surrounded by outspread legs: 2 feet wide* and 2 inches high.
*The number includes the spider's body and its legs; the actual body diameter is about a third of the total.