This is the commonest of all the Bombycoidæ. It may be found at rest on tree trunks and palings during the daytime throughout the summer. Its fore wings are pale grey, with four conspicuous black marks, one of which—that in the anal angle—resembles the Greek letter psi (ψ) placed sideways.
The larva is black or very dark grey, with a pale yellow line down the back, and a black hump on each of the fifth and twelfth segments, that on the fifth being much larger than the other. It feeds in the autumn on lime (Tilia vulgaris), blackthorn (Prunus spinosa), whitethorn (Cratægus oxyacantha), fruit trees, and various other trees, shrubs, and herbs.
The moth called the Dark Dagger (Tridens) is hardly to be distinguished from Psi. It is not really any darker, and its markings are almost exactly similar; but the larva is very different.
The Poplar Grey (Acronycta megacephala)
This is also a very common moth, to be found in all the southern and midland counties, wherever poplars abound, during June and July.
Its fore wings are grey, marbled with a very dark grey. A little inside the middle of these wings, near the costa, is a round spot with a dark centre. This spot is represented in a large number of the Noctuæ, and is known as the orbicular. It will be observed that in the present species it is very distinct.
The caterpillar is dark grey, with a line of black dots down the back; and it has a number of little warts, bearing hairs. On the back of the eleventh segment is a rather large pale spot. It feeds during August on various species of poplar, and changes to a chrysalis in a crevice of the bark.