ABSTRACT

Social organization in the subclass Acari involves parental care and various forms of communal behavior. I first describe subsocial behavior in two spider mite species and then discuss three examples of complex subsociality in Prostigmata and two in Mesostigmata. Aggregation within a narrow space is a common trait observed in all subsocial species. The deposition of feces at certain places (or other nest sanitation behavior) is also common to these species. Subsociality in the Acari is always associated with malehaploid or thelytokous genetic systems, and kin selection under male–haploid genetic system may be important in the evolution of sociality. I next discuss why there is no evidence of eusociality in the Acari, although highly developed subsociality is observed and high relatedness of individuals is expected. One of the plausible explanations is that their simple neural systems decrease the probability of kin recognition; another possibility is that continuous inbreeding decreases the likelihood of the origin of eusociality.

INTRODUCTION

Mites and ticks (Acari) are small organisms with low mobility, and such low mobility may increase the likelihood of interaction among kin. If kin selection (Hamilton 1964a,b) is an important prime mover of social evolution in animals, then we might expect to find examples of sociality in the Acari. However, evidence of social behavior in this group has been scarce; for example, Buskirk (1981) included only 40 lines describing mite behavior in a review of arachnid sociality.