Monstrous Spider, Gargantuan (CR 8)

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

AC: 19 (-4 size, +3 Dex, +10 natural), touch 9, flat-footed 16
Hit Dice: 16d8+32 (104 hp)
Fort +12, Ref +8, Will +5
Speed: 30 ft., climb 20 ft.
Space: 20 ft./15 ft.
Base Attack +12; Grapple +31
Attack: Bite +15 melee
Full Attack: Bite +15 melee
Damage: Bite 2d8+10 and poison
Special Attacks/Actions: Poison, web
Abilities: Str 25, Dex 17, Con 14, Int -, Wis 10, Cha 2
Special Qualities: Vermin
Skills: Climb +14, Hide -5*, Jump +7*, and Spot +4*
Advancement: 17-31 HD (Gargantuan)
Climate/Terrain: Temperate forest
Organization: Solitary
Treasure: 1/10 coins, 50% goods, 50% items

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: 20 feet wide* and 5 feet high.
*The number includes the spider's body and its legs; the actual body diameter is about a third of the total.