The biological significance of the attachment of immature stages ofSimuliumto mayflies and crabs

Abstract

SummaryIt is suggested that the attachment of the immature stages of certain species ofSimulidaeto mayfly larvae and to crabs is primarily an adaptation whereby the immobileSimuliumpupa can obtain protection against disorientation with respect to the current, and against damage, in an environment where available inorganic substrata are liable to be displaced by violent water movement.The principal evidence for this is that these associations typically occur in fast-flowing streams or rivers, and that the attached stages ofSimuliuminclude a disproportionately high number of pupae and large larvae. Any direct benefit theSimuliumlarvae themselves may derive from the association is regarded as a secondary feature of it.Certain responses to physical factors, which might be expected insimuliumlarvae achieving successful attachment, are briefly discussed.