Yes, creatures travel in small groups, following the leader (creature with highest level). There is no limit for number of creatures in the group, so yes, these groups can be quite huge.
The good thing is that marines who patrol the camp - also gather in groups
and they are fair more effective with ranged weapons so they should handle creatures on camp territory easily.
Current AI is all about walking in groups and wandering around - without any clear task. I'd say it is ~10% of what AI is expected to be.
For the next version (January,15-25th) i'll try to make a "lifestyle" for bots - e.g. some constant action that should bring life to the game world. For example, marines patrol the camp, mutons launch coordinated attacks, couriers running and delivering packages, people wander on the streets, etc. Here is the list of TODOs for the next major release (0.97):
- Living Quarters. Players will be given a room where they could store items or rest.
- add Factions.
- add Karma. Karma will affect player's relations with othe factions.
- add capability of switching between attack modes for some weapons.
- add more objects
- improve bots' AI to behave in more "intelligent manner"
btw. regarding your problem with hordes of aliens:
You can talk to Corp. Johnson at the coalition bunker and ask him to give you teammates - they will follow and protect you.
btw, Corp. Johnson also gives you first real quest for muton heads. It appears on Quests page (press'Q') when you receive it - and after you bring him back 2+ muton heads it will be completed.