That would be neat actually. You should post that somewhere in the suggestions section though, it isn't currently possible to make either venoms that directly reduce one's attributes or creatures of entirely different species that congregate together in packs. You could perform the second by giving a creature wildly varying castes though... That ought to be possible for this program to do, actually.
Caste structure variations:
Normal; two identical castes besides male/female variation and possible name variation.
Mono-caste; creature has one caste type. Harpies, satyrs, etc...
random differentiation; all members of same species but having the majority of attributes defined per-caste and having as few tags outside the caste definitions as possible. Would act similar to what DrKill's suggestion would in that they appear to be different species in the same group, even though that's impossible right now. I'm fairly certain this will work, as far as physical structure and diet goes ([GRAZER] can be split between castes, and one or more could have or lack it. Don't know about [BONECARN] or [CARNIVORE], or if the game currently permits silly things like a grazing bone-eating carnivore.
Can't test eating habits easily in the arena at least.)
insect-hive variation; all castes similar, varying by the inclusion or removal of certain non-vital body parts and size differentiation, syndromes, flight/no flight. This would work best if the castes are each named separately and there's some code that assigns tasks (swampbeast queen, egg-layer, soldier, worker, drone, scout, tunneler, etc...) and ensures they have something that makes them more fit for that task. ie: scouts are small, fast, variations that aren't meant for actual fighting or work, maybe a larger view-range, workers/tunnelers would have more strength and ome grasping ability even though they're relatively small. Queens/kings(males are usually called drones) should have better mental attributes as they control all hive activities. Egg-layers/reproducers, if they aren't lumped in as a queen/king, would have no real changes, besides maybe being larger, and would have a greater-than-average [LITTER_SIZE]. Soldiers/warriors of course have better physical attributes and may be venomous/spray poison globs. Queens/Kings should be much rarer.
You could then assign genders to the castes, ensuring that a species has at least one male and one female caste. (I don't think they can ever be both though, so mono-caste creatures can only have one gender.) It can choose one more time to decide if each caste-type will have a male and female copy, if the gender will be assigned randomly for each caste with only one copy -including/excluding no-gender castes-, or if any more castes will receive genders after the first male/female castes.