The Baby Spider appears in Zombotron 2 (game) and Zombotron 2: Time Machine as an adversary. It is considerably smaller than a Normal Spider, due to the fact that it is a baby version of the Normal Spider. Even though it is small, it is very dangerous to the player, because their bites inflict plenty of damage and they are hard to hit with a gun. Presumably, the Boss Spider creates this, similar to how spiders in the real world work.
Explosive and automatic weapons and shotguns work well against Baby Spiders, because the explosion or bullet spread has a greater chance of killing it than an accurate but slow weapon.