This caddis-fly larva is rather rare in Europe, but abundant in many waters in the Netherlands. At first I thought this to be an Oxyethyra species, but those larvae have more flask shaped cocoons. In the year that I found it, there wasn't much literature to be found, but I found a characteristic Russian sketch on the web, so I boldly wrote down this name. Presently, you can find much more information and it proved to be the right name. Strong indications: the short fore legs and the extremely elongated mid and hind legs.
Watch him strolling like a micro T-rex on the picture on the right. This is a genus of the somewhat special family of microcaddisflies or 'purse-case caddisflies', the Hydroptilidae, within the Trichopterae order (caddisflies). The family is distinctive in a number of things.
They are called microcaddisflies because of their small size (a few millimetres). The cocoons are flat like a soft spectacle case (hence 'purse-case') and are entirely made of their own silk, without other material (there are some species however, that cement very fine sand or small pieces of moss to it, and other that mix algae in it).
In contrast with normal caddis-fly larva, they only start building their
cocoons after a few moults, and not before that they get their peculiar vertical flat shape.
They feed on filament algae. Some species of micro-caddis-flies spin silk threads between
water plants, on which they walk with their clawlike front legs with surprising elegance.