Option b. Some ants take over other's colonies and use them for workers.
Explanation:
In English, the possessive form is formed by adding 's at the end of a noun, except if the noun is in its plural form, in which case we add just the apostrophe at the end of the noun, for example, "the teachers' books". In the sentence provided in the question, the possessive form of other should be used in its singular form and not plural, therefore the use of 's.
Okay, I do not know if this is a million percent correct and I am really really sorry if it is not but I hope it at least helps or helps put it in some form of order!!
