Crabs hint:
In Level 1, look at every cave because crabs pop out of each of them. In Level 2, always look around you at the second cave and the rest of the level. Crabs appear everywhere.
Conserving ammo on Level 2:
On Level 2, do not use all your shotgun shells on the huge beetles. Instead, shoot one shell at each bug that gets near you. A dinosaur fight awaits you after opening the gate.