The adults are large moths with broad wings. The hindwings will often be broader than the forewings, and can be seen when the moth is resting. This species is usually light reddish brown, but can be a very dark brown. There are several cross-lines and dotted crosslines. This species can range from 40 to 70mm.
In the first instar the caterpillar feeds entirely on its own egg-shell and is unusual in that it mimics an ant or small spider. This is due to the long thoracic legs "and caudal appendages which are ever nervously twisting about". If the larva is disturbed during this period it wriggles about violently in the same manner as an injured ant. "The young caterpillars keep guard over their own egg-shell. They keep nervously moving around and about this, and if perchance another caterpillar should approach within touch of it, a vigorous attack is made to drive off the intruder." After the first skin change the larvae feed on the leaves of Oak, Beech, Birch or Hazel. During the following instars the caterpillar develops even more of an odd appearance with "a large head, (the) long thoracic legs, raised humps on the fourth to seventh segments and a greatly swollen anal segment that has the claspers modified into long thin structures". The general colour is reddish brown and if in its resting position provides perfect cryptic camouflage. The larvae can grow to a length of 70 mm and if disturbed by a potential predator can put on a menacing display with the thoracic legs splayed out and the head arched back over the body. The moth pupates in a strong cocoon, "usually spun up between dead leaves". The moths emerge the following year from May until July depending on conditions.
Status & DistributionEdit
This species is widespread in southern Britain, but very rarely occurs in large numbers. This species is a rare immigrant in the Channel Islands, and is scarce in Ireland. The adults fly from May till July.