This is just one of three species found mainly on Sallow. It is however sometimes reported feeding on Poplar. The adults are rarely seen and we have no idea how they look like. Most Nematus species however are similar to the Arge species, only slightly bigger. In the Nematus genus most members are black with orange or yellow or entirely black.
The larvae however are quite characteristic and more often seen. They are green with a pattern of black dots and stripes. There is a yellowish band behind the head and the tail is yellowish too. In older larvae the yellow spreads over several segments. The head is black. They live together, often in great numbers. The leaves of the host plant are eaten from the sides on which the larvae sit. The larvae of Nematus miliaris also assume the well known S-position when they feel threatened. Hundreds of animals, if not thousands can sometimes be seen on one tree alone. The larvae pupate underground. Usually there are two broods a year. The adults are on the wing in May and June and again, after a short break, in July and August. The eggs are deposited in the skin of twigs of the woodplant in two bunches, shaped as rings around the twig.