Notes
Tarantulas usually come in groups, with other weaker monsters or together with a Giant Spider (in the Plains of Havoc for example). Kill the weaker monsters off first so they do not break your shielding. Also note that tarantulas are dangerous in groups, as they can do quite a lot of damage. GFBs work nicely to kill the tarantulas and the other creatures. Hide is the tarantula boss.
Abilities
Melee (0-90) and Poisons you for 1-2 hp/turn, Haste, Terra Strike (doesn't do damage).
Damage Taken From Elements
Location
Tiquanda Tarantula Caves, Trapwood ground level and underground, in 2 small caves South of Thais, Dark Cathedral, single spawn on top of Crocodile den north of Port Hope (here), Plains of Havoc, underground Liberty Bay, Nargor and other constituents of the Shattered Isles. First floor up in the big building in the Cemetery Quarter After the summer update of 2008, tarantulas can be seen on the beginner's island of Rookgaard.
Strategy
Knights: Can kill them with ease with around 60/60.
Paladins: Level 20 to outrun them and around 50 distance to not waste ammunition, although a level 25 paladin with skills 60/50 can handle 2 of them with no problem, but will have to use antidote.
Mages: Use Mana Shield if you are a low level. Wand or rod and runes to kill faster. Sorcerers can use Fire Wave to kill a group of Arachnids while Druids could use Ice Wave to kill multiple Arachnids.
Loot
0-40 gp, Brass Legs, Plate Shield, Steel Helmet (semi rare), Time Ring (very rare).