In Britain, as well as in parts of Northern Europe, a Noctuid moth, Charaeas graminis, occasionally increases to an enormous extent: its larva is called the Hill-grub and lives on the grass of pastures, frequently doing great damage in hill-lands. The increase of this moth seems to take place after the manner of an epidemic; a considerable number of years may pass during which it is scarcely seen, and it will then appear in unusual numbers in widely separated localities. This moth lays a large number of eggs, and is not completely nocturnal in habits; sometimes it may be seen on the wing in great numbers in the hottest sunshine, and it has been noticed that there is then a great disproportion of the sexes, the females being ten or twenty times as numerous as the males. In Australia, the Bugong moth, Agrotis spina, occurs in millions in certain localities in Victoria: this moth hibernates as an imago, and it formerly formed, in this instar, an important article of food with the aborigines. The powers of increase of another Noctuid moth—Erastria scitula—are of great value. Its habits have been described by Rouzaud.[[313]] On the shores of the Mediterranean the larva of this little moth lives on a Scale-Insect—Lecanium oleae—that infests the peach; and as the moth may have as many as five generations in a year, it commits laudable havoc with the pest. The larva is of remarkable form, very short and convex, with small head, and only two pairs of abdominal feet. The scale of the Lecanium is of larger size than is usual in that group of Insects, and the young larva of the Erastria buries itself, as soon as hatched, in one of the scales; it destroys successively numerous scales, and after having undergone several moults, it finds itself provided, for the first time, with a spinneret, when, with the aid of its silk, it adds to and adapts a Coccid scale, and thus forms a portable habitation; this it holds on to by means of the pair of anal claspers, which are of unusual form. The case is afterwards subjected to further alteration, so that it may serve as a protection to the creature when it has changed to a pupa. This moth is said to be free from the attacks of parasites, and if this be the case it is probable that its increase is regulated by the fact that when the creature becomes numerous it thus reduces the food supply, so that its own numbers are afterwards in consequence diminished.
One of the most remarkable genera of British Noctuidae is Acronycta,[[314]] the larvae of which exhibit so much diversity that it has been suggested that the genus should be dismembered and its fragments treated as allied to several different divisions of moths. There are many points of interest in connection with the natural history of these Acronycta. A. psi and A. ridens are practically indistinguishable as moths, though the larvae are easily separated: the former species is said to be destroyed to an amazing extent by parasites, yet it remains a common Insect. The genus Apatela is very closely allied to Acronycta, and Harris says that "Apatela signifies deceptive, and this name was probably given to the genus because the caterpillars appear in the dress of Arctians and Liparians, but produce true owlet-moths or Noctuas."[[315]] The species of another British genus, Bryophila, possess the exceptional habit of feeding on lichens. Some of the American group Erebides are amongst the largest Insects, measuring seven or eight inches across the expanded wings.
The Deltoid moths are frequently treated as a distinct family, Deltoidae, perhaps chiefly because of their resemblance to Pyralidae. At present, however, they are considered to be separated from Noctuidae by no valid characters.
Fam. 38. Epicopeiidae.—The genus Epicopeia consists of only a few moths, but they are amongst the most extraordinary known: at first sight they would be declared without hesitation to be large swallow-tail butterflies, and Hampson states that they "mimic" the Papilios of the Polyxenus group. Very little is known about these extremely rare Insects, but the larva is stated, on the authority of Mr. Dudgeon, to surpass the moths themselves in extravagance; to be covered with long processes of snow-white efflorescence, like wax, exuded from the skin, and to "mimic" a colony of the larva of a Homopterous Insect. Some ten species of this genus are known from Java, India, China, and Japan. In this family there is said to be a rudimentary frenulum, but it is doubtful whether the hairs that have given rise to this definition really justify it.
Fam. 39. Uraniidae.—A family of small extent, including light-bodied moths with ample wings and thread-like antennae; most of them resemble Geometridae, but a few genera, Urania and Nyctalemon, are like Swallow-tail butterflies and have similar habits. The Madagascar moth, Chrysiridia madagascariensis (better known as Urania rhipheus), is a most elegant and beautiful Insect, whose only close allies (except an East African congener) are the tropical American species of Urania, which were till recently treated as undoubtedly congeneric with the Madagascar moth. The family consists of but six genera and some sixty species. The question of its affinities has given rise to much discussion, but on the whole it would appear that these Insects are least ill-placed near Noctuidae.[[316]] The larva of the South American genus Coronidia is in general form like a Noctuid larva, and has the normal number of legs; it possesses a few peculiar fleshy processes on the back. A description of the larva of Chrysiridia madagascariensis has been widely spread; but according to Camboué,[[317]] the account of the metamorphoses, first given by Boisduval, is erroneous. The larva, it appears, resembles in general form that of Coronidia, and has sixteen feet; it is, however, armed with long, spatulate black hairs; it changes to a pupa in a cocoon of open network.
Fig. 206—Abdomen of Chrysiridia madagascariensis. A, Horizontal section showing the lower part of the male abdomen: 1, first segment; 2, spiracle of second segment; 4-8, posterior segments. B, the abdomen seen from the side, with the segments numbered. The section is that of an old, dried specimen.
In all the species of this family we have examined, we have noticed the existence of a highly peculiar structure that seems hitherto to have escaped observation. On each side of the second abdominal segment there is an ear-like opening (usually much concealed by overlapping scales), giving entrance to a chamber in the body; this chamber extends to the middle line, being separated from its fellow by only a thin partition. At its anterior and lateral part there is a second vesicle-like chamber, formed by a delicate membrane that extends as far forwards as the base of the abdomen. There can be little doubt that this is part of some kind of organ of sense, though it is much larger than is usual with Insect sense-organs.
Fam. 40. Epiplemidae.—Under this name Hampson has assembled certain Geometroid moths, some of them placed previously in Chalcosiidae, some in Geometridae. They form a varied group, apparently closely allied to Uraniidae, and having a similar peculiar sense-organ; but are distinguished by the presence of a frenulum. The larva seems to be like that of Uraniidae.
Fam. 41. Pyralidae.—This division is to be considered rather as a group of families than as a family; it includes a very large number of small or moderate-sized moths of fragile structure, frequently having long legs; antennae simple, only in a few cases pectinate; distinguished from Noctuidae and all the other extensive divisions of moths by the peculiar course of the costal nervure of the hind wing, which either keeps, in the middle of its course, near to the sub-costal or actually unites with it, subsequently again separating. Members of the Pyralidae are found in all lands; in Britain we have about 150 species. The larvae are usually nearly bare, with only short, scattered setae, and little coloration; they have most varied habits, are fond of concealment, and are very lively and abrupt in movement, wriggling backwards as well as forwards, when disturbed; a cocoon is formed for the metamorphosis.