A SPECIES of Chironomidae (Diptera) the larvae of which were living on the wing pads and legs of the immature stages of Acroneuria abnormis (Newman, 1838) (Plecoptera, Perlidae) in streams around Ithaca, New York, has been reported1,2. Nothing has been added to our knowledge of this peculiar association since then. From May 1963 to January 1964 I observed what seems to be the same species in a stream near Wolf Lake, Pontiac County, Quebec. From larvae collected on their hosts, the other stages of metamorphosis have been reared and described as representative of a new species and a new genus of Orthocladiini [sub-familia Orthocladiinae], Plecopteracoluthus downesi3. The larvae fed on small particles, not on the Plecoptera themselves; thus the association is not parasitism, as had been suggested earlier, but rather it is phoresis.