Life history of Metacnephia lyra, a blackfly highly characteristic of large Swedish river rapids at the time of maximum discharge (Diptera : Simuliidae)

Larvae of the blackfly Metacnephia lyra (Lundstrom) occur in huge numbers i n rapids of unregulated rivers in northern Sweden. Despite its high abundan ce, and hence potential importance for particle transport and predation pro cesses, its biology is poorly described, if at all recognised. This study r eports on features pertaining to the life cycle, growth, habitat, and preda tors of the aquatic stages. Larval development takes place from mid May to late June coinciding with maximum discharge. From size distributions seven larval instars were categorised; the head width increased allometrically wi th an increment of 0.081 mm per instar. The rapid growth rate (daily growth rate: 0.0058 * body mass(-0.63)) is apparently accomplished by a unique ca pacity to utilise habitats with very fast current velocities and thereby hi gh food particle delivery rates. Moreover, predation on M. lyra larvae seem s of limited significance, since relatively few of them were encountered in the guts of predators.