In the context of the passage by Jake Buehler, the likening of Staghorn ferns to termites is primarily because both are suspected to exhibit behaviors related to social structures. Therefore, the best answer is B. Termites are eusocial like he suspects Staghorn ferns to be.
This suggests that Buehler is drawing a parallel between the social behavior of termites, which are known for their eusocial organization (living in colonies and working together), and the potential social behavior of Staghorn ferns, which he proposes may work together in a similar manner.