Question

one of the largest bat colonies is in texas.

Explanation:

The word "colonies" refers to a group or community. In the context of the sentence "One of the largest bat colonies is in Texas," we are talking about what (the thing, in this case, a group of bats). "Who" is used for people, and since "colonies" here is about bats (not people), "what" is the appropriate choice.

Answer:

what