In the perfect state Lepidoptera feed principally upon nectar which they derive from flowers and, among other sources of food, honey dew and over-ripe fruit are also resorted to. Decaying fruit, for example, is attractive to the red admiral (Vanessa atalanta) and certain other butterflies, while the purple emperor (Apatura iris) is well known to visit carrion. Certain flowers are more at tractive to Lepidoptera than others, and in Europe the flowers of jasmine, honeysuckle, valerian, heather, ivy, sallow, syringa, privet, petunia and ragwort are much visited by moths, while butterflies are especially partial to bramble, thistle and Buddleia. Butterflies and certain moths are diurnal insects, but the majority of the members of the order are crepuscular or nocturnal. Some moths fly both by day and at night, while others are seldom known on the wing before midnight, and after dark almost the whole of the Noctuidae are attracted to the moth collectors' sugar mix ture. During the winter, in cold and temperate lands, most Lepidoptera hibernate either as larvae or pupae; some, such as the hairstreak butterflies, overwinter as eggs, while certain of the Vanessae and other butterflies, along with a number of moths, pass the dormant season as perfect insects. Many Lepidoptera are double-brooded in that two complete life-cycles are passed through in the year; others, given a sufficiently high temperature, may pass through four or five generations in that period, particularly species infesting stored grain, meal, etc.
The sexual differences in Lepidoptera are often well marked ; in some families the antennae are pectinated in the males and simple in the females, or these organs may be pectinated in both sexes, but much more pronounced in the males (fig. r). The special sensory organs located on the antennae are greatly developed where those appendages are highly pectinated, and give to the males their re markable power of finding their mates. The phenomenon known. as "assembling" is especially pre valent in the Lasiocampoidea as well as in some other moths, and is believed to be of the nature of an olfactory response. The fe males apparently emit an odour attractive to the opposite sex, and under favourable conditions a freshly emerged example will attract many males, which fly up to her against the wind. In many Lepidoptera the sexes differ greatly in size and coloration, as for example in the gipsy moth ; among the Lycaenidae the males of numerous species are brilliant blue and the females of a brownish hue. In the tropical Papilionidae the sexes are often totally dif ferent in coloration as well as exhibiting differences in form. Other examples of sexual dimorphism are afforded by those moths whose females are either wingless or have the wings reduced to use less vestiges, the males being fully winged. This peculiarity occurs
in distantly related families and has consequently been independ ently evolved. Notable examples are found in the bag-worm moths (Psychidae), vapourer moths (Orgyia), and in about half a dozen genera of geometrid moths.
Another interesting feature is the occur rence of different seasonal forms among certain butterflies : these are so different in coloration that they were regarded as separate species until their relationships were worked out. One of the best known examples is afforded by the European Araschnia levana, whose spring form is known as levana and its summer form, prorsa was first described under that name as a different butterfly. In the tropics certain species occur in definite wet sea son and dry season forms, and the North American swallow tail I phiclides marcellus has three distinct seasonal forms. Those which emerge from over-win tered pupae in the early spring are of the form marcellus and those that appear somewhat later are of the form telamonides ; the summer butterflies, produced from eggs laid the same season, are different from either of the spring forms and are of the type named lecontei. There are, again, other butterflies, such as the Afri can Papilio dardanus, which have several and quite different forms in the female which closely mimic other species of Lepidoptera. For a discussion of this and other cases of polymorphism see MIM ICRY. Extensive experiments have been conducted by Weismann, Merrifield, Standfuss, Fischer and others upon the effects of tem perature on seasonal and other types of coloration. Thus A. Weis mann showed that when pupae destined to produce the summer form prorsa of Araschnia levana were kept at a low temperature they gave rise to the form levana or to a form intermediate be tween it and prorsa. By raising the temperature it proved exceed ingly difficult to change the form levana into prorsa and in most cases it was a failure. Weismann concluded, therefore, that the species was a northern one and that the form levana was the older and more constant, and that prorsa was a later acquired form, and consequently more readily influenced. By the application of cold, individuals of Vanessa urticae indistinguishable from the northern variety polaris have been produced ; also, pupae of the summer form of Pieris napi when placed on ice gave rise to the winter form of that butterfly. By raising temperature to the requisite extent and applying it at the susceptible period it has been possible to change the female coloration of two butterflies, Parnassius apollo and Gonepteryx rhamni into that of their respective males.