Wingspan 9–10 mm.
A. aeratella is a very small dark grey moth, having a purple shine when fresh.
The antennae are rather short: nearly half the size of the forewing.

The yellow caterpillar lives from July to May and hibernates in a gall.

The presence of the larva induces the formation of a fusiform and often reddish gall of about 15 mm on the hostplant.
See also bladmineerders.be.

When young, the caterpillar lives on and inside a flower of the hostplant causing the formation of a reddish spindle-shaped swelling. Later on, when fully grown, the caterpillar cuts the gall loose, leaves the flower, and moves around on the stem of the plant carrying the gall with it. The gall, with the larva inside, can be found standing mostly perpendicular to the stem. Eventually, the larva pupates inside its gall in May.
The adults are also active during daytime.

This species lives almost exclusively on Polygonum aviculare (common knotgrass) but also Polygonum arenarium, P. patulum, P. romanum and, even more rarely, Persicaria lapathifolia are accepted.

The species probably has a preference for limestone areas. The original habitat, a rather narrow valley with a small, winding river between lush vegetation has been destroyed by the construction of a holiday resort which has subsequently been abandoned.