Aims To record and elucidate the phylogeny and biogeography of a species swarm of the genus Hydropsyche (Insecta, Trichoptera) in the Philippines. All species belong to the hamifera group.
Location The Philippines and neighbouring areas.
Methods A phylogenetic analysis based on variation of morphological characters of the male phallic apparatus.
Results The species swarm is differentiated into three clades of different age.
Conclusion Alternative dispersal and vicariance hypotheses are considered in an attempt to explain the colonization of the Philippine archipelago and the subsequent ramification of the group. The vicariance hypothesis based on the late Miocene accretion of continental fragments to the Philippines appears to be the most parsimonious. The evolution of the swarm occurred on the Philippines. Later on species dispersed to Borneo, Sulawesi and the Moluccas. The species swarm has undergone an adaptive radiation which enabled the simultaneous occurrence of species in the same streams.