The caterpillar has a rough green skin, sprinkled with white dots, and marked with seven oblique white lines on each side, each of which is bordered with dark green above. The spiracles are pinkish, surrounded by violet rings; and the horn is blue. The moth flies during May, June, and July; and the caterpillar may be found in plenty during August, feeding on the apple, willow (_Salix alba_), sallow (_S. cinerea_ and _S. Caprea_), poplar (_Populus alba_ and _P. nigra_), aspen (_P. tremula_), and the blackthorn (_Prunus spinosa_). As with many other _Sphinges_, the larvae are much more commonly seen than the perfect insects; but the latter may often be met with resting on tree trunks and fences in the neighbourhood of their food plants. _The Poplar Hawk_ (_Smerinthus Populi_) [Illustration: FIG. 101.--THE POPLAR HAWK.] This moth is very common and very widely distributed, and may be easily found in any of its stages. The perfect insect flies during May, June, and July; and being rather heavy on the wing, it is easily taken with a net as it hovers round the branches of its favourite trees or among the flowers of gardens at dusk. The larva may be beaten from the boughs of poplars and sallows during August and September, and during the latter month may often be seen creeping down and around the trunks of these trees, searching for a suitable spot in which to undergo its changes. The pupa may be dug out of the soil at the foot of the same trees during the autumn, winter, and spring months. The fore wings are ashy grey or greyish brown, marbled with darker tints, with a conspicuous white spot near the centre. The hind wings are similarly coloured except at the base, where there is a large patch of brick-red. The caterpillar is rough, of a pale green colour dotted with yellow, with seven oblique yellow stripes on each side. The spiracles are white, edged with red; and the horn is yellow on the upper, and reddish on the under side. Its chief food plants are the poplar, the Lombardy poplar (_Populus pyramidalis_), aspen (P_. tremula_), and sallow (_Salix Caprea_ and _S. cinerea_). _The Lime Hawk_ (_Smerinthus Tiliae_) This beautiful moth (fig. 5, Plate IX) is easily identified by its rich olive green and brown wings, the fore pair of which have very conspicuous patches of deep olive, sometimes uniting to form a continuous central bar. It flies in May and June. The caterpillar is rough, of a pale green colour, dotted with yellow, with seven oblique yellow stripes on each side. Thus it is very like the larva of _Populi_, but may be distinguished from that species by the orange spiracles, and by the horn, which is rough, blue above, and yellow beneath. Behind the horn, too, there is a flat purple or violet scale with an edging of orange.