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A medium-size (3.3-4.0 cm. wingspans) grey and grey-brown moth. The forewing is obscurely banded, with a small yellow-gold spot near the wing base and another at the reniform. The hindwing is dark brown. Most easily confused with G. lintneri, which is paler, especially on the hindwings, and which lacks the gold spots on the forewings. The antennae are pectinate (broadly in male, narrowly in female). The three large species of Gluphisia can also be separated by male genitalic characters, notably the shape of the juxta, transtilla and uncus. In avimacula, the uncus is moderately excavated, the lobes broadly acute, the lobes of the transtilla are long and acute, the juxta broad and widely excavated with the lobes narrow and rounded.

The Avimacula Pebble emerges from the pupae in the spring a week or two after Lintner's Pebble. The adults are nocturnal and come to light. The larvae are solitary defoliators, and they overwinter as pupae. There is a single brood annually.