Which is perfect!
I was originally thinking that I might go ahead and write up some monsters, but it appears it's already been done! WOOO!
An excellent place to find some monsters is the Swords & Wizardry SRD
Here are a few select monsters to add to the campaign from the S&W SRD
The Flytrap Shambler
The Assassin Vine
Here's my take on a few monsters:
4; 7 ; 1 Mouth/bite (swallows) Damage: 1d6, 13; 0; 120; : Swallow whole*
*A Giant Venus Fly trap will try and bite its prey, on a successful attack it will do 1d6 damage, players are allowed a save, on a fail they are swallowed 2d6 damage. If they are not rescued from the plant in 1d6 rounds they will perish.
1; 9 ; 1 vines Damage: 1d6, 17; 0; 15; : constriction*
Creepers will flail out with their vines causing 1d6 damage. On a failed save a PC will be constricted by the vine, slowly squeezing them of their breath, they will receive 1d6 damage while constricted.
The other thing I realized that I'm going to need are tropical birds, and apes, which will all probably be low HD type monsters. My sorta standard is 1hd, AC 10, dmg 1d3 kinda thing. Mostly just nuisances to the players.
Oh and Insects!
Mantis, Giant Praying