Eriogaster catax, commonly known as the eastern eggar, is a species of moth in the family Lasiocampidae.
Eriogaster catax has a wingspan of 27– in males, of 35– in the females. This species shows a pronounced sexual dimorphism. The males are smaller and have feathery antennae. In males the basal part of the front wing is yellow-orange, while the outer part is pinkish-brown. In the females the front wings are browner. In both sexes, the front wings show a transversal line and a white discal spot within a dark border. Hind wings have no markings. Females are larger and at the end of the abdomen they have a tuft of dense gray-black hairs.
The eggs hatch in April. The larvae feed on Crataegus, Quercus, Betula, Populus, Prunus and Berberis species. This univoltine species fly at night in September and October.
It is found in Austria, Belgium, Bulgaria, Czech Republic, Germany, Hungary, Italy, the Netherlands, Poland, Serbia and Montenegro, Slovakia, and Spain.