Despite their climbing abilities, the mul'niessa do not particularly prefer the spider. The scorpion is more to their taste. (Also read: mul'niessa are not drow).
Giant Spider Companions
Starting Statistics: Size Small; Speed 30 ft., climb 30 ft.; AC +0 natural armor; Attack bite (1d4 plus poison); Ability Scores Str 6, Dex 17, Con 10, Int —, Wis 10, Cha 2; Special Attacks poison (frequency 1 round ,effect 1 Str damage, cure 1 save, Con-based DC); Special Qualities darkvision, tremorsense 30 feet; CMD trip +12.
4th-Level Advancement: Size Medium; AC +1 natural armor; Attack bite (1d6 plus poison); Ability Scores Str +4, Dex –2, Con +2.