Distinguished from H. fuciformis by the narrow band of scaling along the outer margin of each wing and the presence of an undivided forewing cell. Although some confusion may arise with freshly-emerged examples which have their entire wings covered with loose, grey scales, these are lost after the first flight, after which identification is made easier by a near absence of variation. In such localities, vast numbers can be found in some years but very few in others, though it is never totally absent. Although mimicking a bumble bee in coloration, its flight is much more rapid and agile. Its skill is superbly demonstrated during courtship when pairs chase each other low over the ground as well as spiralling upwards like a whirlwind.
Copulation generally follows, with pairs remaining in copula for up to two hours.
Bivoltine farther south, during late April or early May, and again in August. Laid singly on the underside of a leaf of the hostplant, with up to six per plant or group of plants not uncommon. The newly-hatched, white larva is about 3mm long and covered with small black tubercles bearing forked, black hairs. The caudal horn is small with two black hairs at its apex. The body is very rough to the touch.