jwjranger:

well if these things do attack i have a suggestion, i have 2 blue tounge lizards and the main cause of death for them is whipper snippers cause they just sit there opening their mouths (signaling their going to attack) and then... well you get the idea so what if lets just say... a tank was going across a river and a swarm of eel things (if there small) came and started biteing it, but did no damage. just a though cause not everything can do damage to all other things.

Yes, I also would think that diversity of danger is important. Not every unit should be suceptible to ambient life. 

Also, maybe there should be signs of life... I mean, if there is a river or small lake, we should have an inkling (maybe) that there are dangerous animals in there.  Or maybe it is more interesting to wonder if you are crossing a safe or dangerous river.....