This family—the Ægeriadæ of some authors—has over one hundred Palæarctic species assigned to it; these are distributed among five genera, two of which are not represented in Britain. Fourteen species are found in the British Isles, but to obtain fine specimens of most of them the mature caterpillars or the chrysalids will have to be collected and the moths reared. All species emerge from the chrysalis early in the forenoon, and then only under the influence of sunshine.
The caterpillars are somewhat maggot-like, and live in stems, branches, and roots of trees and shrubs; or in the crowns and roots of low-growing plants. The majority, possibly all, are nearly two years in arriving at full growth.
As indicated by the English name this moth, and also that next to be mentioned, are very like the hornet (Vespa crabro). On turning to Plate 154, Fig. 1, it will be seen that this species has a yellow head and patches of yellow on the shoulders; these characters at once separate it from T. crabroniformis.
The caterpillar is yellowish white, with a red brown head, and a yellow plate on the first ring of the body. It feeds on the roots and lower portion of the trunks of poplar. The brown shining chrysalis is enclosed in a cocoon of wood scrapings woven together with silk. The moth is out in May and June; and has been found, newly emerged, sitting on stems of poplar in the morning.
The eastern counties of England appear to be most favoured by this species, but it also occurs northwards to Yorkshire, southwards to Devonshire, and a specimen has been recorded from Rhyl, North Wales. In Scotland, it has been reported from some localities in the south; Kane states that he has reason to believe that the species occurs in the northern half of Ireland, and that he found caterpillars plentiful in young poplars growing in a marsh near the city of Waterford.
Another hornet-like moth, best distinguished from that just mentioned by the yellow collar behind the black head (Plate 154, Fig. 7 ♀). The male is rather smaller, but otherwise similar.
The caterpillar is yellowish white, with dark brownish head, and a blackish edged yellow plate on the first ring of the body. It feeds in stems of sallow, willow, and poplar. In late June and through July the moth is on the wing, and may occasionally be seen at rest on leaves or stems of sallow, etc.
The species, known also as bembeciformis, Hübner, is generally distributed throughout England, Wales, and Ireland; in Scotland its range extends into Perthshire.
Abroad it seems pretty much confined to Holland, Northern and Central Germany, Austria, and Bohemia.
This species is the Trochelium vespiforme of some British authors, and the Ægeria asiliformis of Stephens and others.
Another English name for it is the Dusky Clearwing, and this refers to the cloudy fore wings.
Stephens, writing of it in 1828, remarks: "Occasionally taken on poplars, near London, in June. I have obtained it from the neighbourhood of Bexley, and from Birchwood; but it is doubtless a rare species, and exists in few collections: of the male, I have hitherto seen but two specimens, one of which I possess." Both places mentioned by Stephens are in Kent, and one or two specimens of the species have since been reported from Ashford in the same county. The late Henry Doubleday took specimens at Epping, Essex. Colney Hatch Wood in Middlesex has also been given as a locality in the past; more recently two specimens have been noted from Chiswick. The example shown on Plate 154, Fig. 4, is of continental origin.
The caterpillar lives under the bark of poplar trunks, and the moth flies in June and July.
As a British species this insect was first noted from Llangollen, in North Wales, somewhere about fifty years ago. In 1867 it was found to inhabit birch woods in the Rannoch district of Scotland, and later on its presence was detected in Sutherlandshire. It has been recorded from Hereford; one example was reported from Wiltshire in 1857; and two from Delamere Forest, Cheshire (1901 and 1905). Kane (Catalogue of the Lepidoptera of Ireland) states that moths have been taken at Killarney, and caterpillars obtained in the same district, and also at Kenmare.
The caterpillar (Plate 156, Fig. 3; after Hofmann) feeds on the inner layer of bark of large birch trees, and is full grown about May. It turns to a dark brownish chrysalis, in a cocoon formed close up to the bark, which thinly covers the outer end of the burrow. The moth flies in June or sometimes July. It is of comparatively large size, and may be distinguished from the next species by the yellow belts on its body, and the chestnut coloured tuft at the tail. (Plate 154, Fig. 2.)