In addition to count, how about adding density as well? By that I mean using a single entity as a group of bugs. For example, if the density is set to '20', then each spawned bug will have 20 times the hit points, and each time it loses 5% of its hit points, a corpse will spawn. That would be a simple, easy-to-code way to handle it. That way, those 140 spawned biters could represent 2800(!) biters without the UPS hit.
You should definitely have an option to float the current density count above each spawned entity so players can keep track of them. You'll need that for debugging, anyway.
(Alternatively, you could track each 'sub-bug' of each spawned entity separately, and either exposed to the system as normal, or some weighted randomness determines which sub-bug gets hit by each attack. I wouldn't bother, though.)
Does that sound reasonable and doable?
Cheers!