Inaccurate?

Spider Companion

( Drow of the Underdark, p. 52)

[General]

Instead of an animal, you bond with a monstrous spider

Prerequisite

Vermin Trainer (DrU) , animal companion,

Benefit

You can select a monstrous spider as your animal companion. This spider gains all the benefits normally granted to animal companions. At 1st level, you can select a Tiny, Small, or Medium monstrous spider as your spider companion. A druid of sufficiently high level can select a more powerful creature as her spider companion, applying the indicated adjustment to the druid's level (in parentheses) for the purpose of determining the spider companion's characteristics and special abilities.

Spider Minimum Level (Adjustment)
Large 4th(—3)
Huge 10th(—9)

Normal

Spiders are not available as animal companions.