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

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Abstract
It is suggested that the attachment of the immature stages of certain species of Simulidae to mayfly larvae and to crabs is primarily an adaptation whereby the immobile Simulium pupa 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 of Simulium include a disproportionately high number of pupae and large larvae. Any direct benefit the Simulium larvae themselves may derive from the association is regarded as a secondary feature of it.Certain responses to physical factors, which might be expected in simulium larvae achieving successful attachment, are briefly discussed.