The young entomologist can hardly expect to meet with this fine insect, for it is very rare, and it is only occasionally that a specimen is seen in Britain; but its characteristics are so striking that we have endeavoured to find it a place here. Reputed British specimens of _Fraxini_ command the price of a few pounds each, but specimens from the other side of the Channel may be obtained for a few pence. With such rarities we should advise a young entomologist to purchase the foreign specimen rather than adopt the two other alternatives--give an exorbitant price for a supposed Britisher, or else remain a stranger to the gem, but all foreign specimens should be labelled according to their nationalities. _The Red Underwing_ (_Catocala Nupta_) The other three members of the family are very similar in appearance, the fore wings of all being marbled with shades of grey, relieved by touches of black and brown; and the hind wings, red or crimson, give the popular names to the species. The Red Underwing flies in August and September, and is common in the southern counties of England, as well as in some of the midland counties; it may be often seen flying by day around willows. [Illustration: FIG. 176.--THE RED UNDERWING.] The caterpillar is similar in form to that of _Fraxini_, and when at rest by day on the bark of its tree it is very difficult to detect, so closely does it apply itself to the surface, and so perfectly does it imitate the colour of its surroundings. It feeds on the crack willow (_Salix fragilis_), sallow (_S. alba_), poplar (_Populus_), and plum (_Prunus_), and is full grown in June. _The Dark Crimson Underwing_ (_Catocala Sponsa_) This beautiful insect is represented on Plate XI (fig. 6). It will be observed that the black band crossing the centre of the hind wing is rather broad and sharply bent--an important feature, since it is the most serviceable distinguishing mark between this species and the Light Crimson Underwing (_C. Promissa_). The caterpillar is similar in form and habits to those of _Fraxini_ and _Nupta_, and feeds on the oak. It is full fed about the beginning of June, when it changes to a chrysalis between leaves which it has spun together with silk. The moth flies in July and August, and is common only in certain oak woods of the southern counties. It is particularly abundant in the New Forest, where scores may be taken in a single night by judicious sugaring. There yet remain a few small families of the _Noctuae_, but we must leave them in order that we may give a proportionate share of our space to the other great division of the larger moths--the _Geometrae_. CHAPTER XX _GEOMETRAE_