Basically, the idea behind this is that Aliens are likely to require chemical compounds or elements in their diets which are either rare or unavailable in terran biology, and are likely not to survive without the proper foodstuffs. So your scientists, if they wanted to keep them indefinitely and maintain the hive mind, would need to figure out what their 'natural' diet was, what, if any exotic chemicals they needed in this, as well as proportions of such things as sodium, potassium, taurine and other amino acids, fatty acids, iron, that sort of thing, so to prevent malnutrition, as well as any substances to avoid. To research a diet, you'd need both autopsy data and at least one live individual in containment. Without a diet for a species, after a certain period of time, varying between species, there would be an X% chance each day, cumulative, that an individual that it would die of malnutrition or toxicity. Some would be pretty fast to die, like anything which needed arsenic instead of phosphorus. I figure a good thing to study would be animal diets in zoos and how they get some animals to feed.
