The spiders in the forest act as follows:

Tiny Black: Show you the path
Big Green: Jumpers (jump, run away, and jump again)
Big Red: Flingers (they spit)
Big White: Flingers (spit paralyzing venom)
Big Multicolor: Possible Jumper/Flinger mix.

Greenhouse: Wizards Card
After talking to Fred and George, go to the right of the greenhouse and cast
Alohomora the hedge separating it from the wall. Follow the passage to a small
courtyard. Cast Alohomora on the statues to get the Card.