The Hydroptilidae are a large family of caddisflies (Trichoptera) with a worldwide distribution. They are commonly known as microcaddisflies or purse-case caddisflies, in reference to two characteristic traits of this family: Hydroptilidae are much smaller than other caddisflies, rarely exceeding 5 mm (0.20 in) in length. Their larvae do not build a protective case until the final instar of their growth. At that time however, they build a typically Purse-shaped case, either portable or stuck to the substrate, in which the larva finishes growth and pupates.[1]
Their systematic placement among the caddisflies is still disputed. They are traditionally placed in the suborder Spicipalpia, which do not seem to be a natural monophyletic group, but rather an evolutionary grade of moderately advanced caddisflies. Some authors downrank the Spicipalpia to a superfamily of the more basal Annulipalpia and call them Rhyacophiloidea (which otherwise refers to a subfamily of suborder Spicipalpia), but recent studies generally rejected this view.[1]
More often, the Hydroptilidae are placed in a monotypic superfamily Hydroptiloidea, either in the Spicipalpia or – probably more appropriately considering the present state of caddisfly phylogeny – incertae sedis in the Trichoptera. It may be that the Glossosomatoidea are particularly closely related to the Hydroptilidae; together they might even be closer to the most advanced caddisflies (the tube case caddisflies, Integripalpia) than any other living caddisfly. But this view is almost as disputed as including the Spicipalpia in the Annulipalpia. In any case, were Glossosomatoidea and Hydroptiloidea to be merged into a single superfamily, the older name Hydroptiloidea would apply for the combined group.[1]
The peculiarly apomorphic genera Palaeagapetus and Ptilocolepus have been separated as subfamily Ptilocolepinae, while all other genera form the Hydroptilinae family with its multiple tribes. It is far from certain that the Ptilocolepinae are the living fossils such an arrangement would imply them to be.
Around 70 genera with at least 1,700 species have been described from this family:[2]
Hydroptila larva The Hydroptilidae are a large family of caddisflies (Trichoptera) with a worldwide distribution. They are commonly known as microcaddisflies or purse-case caddisflies, in reference to two characteristic traits of this family: Hydroptilidae are much smaller than other caddisflies, rarely exceeding 5 mm (0.20 in) in length. Their larvae do not build a protective case until the final instar of their growth. At that time however, they build a typically Purse-shaped case, either portable or stuck to the substrate, in which the larva finishes growth and pupates.
