July 1, 1892.] 



KNOWLEDGE 



123 



hairy brown flies which may be seen in autumn creeping in 

 a sleepy soi't of manner about the windows of houses, and 

 are commonly known as drone-tlies, and scientifically as 

 Eiistalis. These insects, although true flies, with only a 

 single pair of wings, are so like bees (in which, it need 

 scarcely be said, there are two pairs of wings) that it is 

 very diflicult to persuade some persons that they are not 

 really members of that group of insects. Their resemblance 

 to the latter is increased by their similar habits, more 

 especially their bee-like buzz ; and there is no doubt 

 whatever but that they are mistaken by birds for bees, 

 and thereby enjoy an immunity not granted to ordinary 

 flies. 



Again, the gaudy flies marked with bold bands of black 

 and yellow which are so common on fine summer days in 

 gardens, and are known as wasp-flies [Syrphus], take their 

 name from their resemblance to wasps, which in some 

 species is so close as to make it diflicult to convince people 

 that they are not really wasps. 



Less common than the above-mentioned flies are the 

 beautiful British insects known as clear-winged hawk- 

 moths. Some of these, named hornet clear-wings (.S/i/fcca/), 

 so exactly resemble large wasps or hornets that they would 

 deceive nine persons out of ten who are not entomologists. 

 Moreover, they have precisely the same habits as hornets, 

 and when caught will actually curl up their bodies in a 

 wasp-like manner as if about to sting, although they are 

 perfectly harmless. Less complete is the resemblance of 

 other clear-wings — hence known as bee clear-wings — to 

 humble-bees. These insects, as has been well observed, 

 are, however, very important, as proving that their mimicry 

 is an acquired character, since when they first emerge from 

 the chrysalis their wings are thinly covered with the well- 

 known minute scales characteristic of ordinary moths, 

 these scales soon falling ofl" and leaving the wings per- 

 fectly transparent. This indicates that the ancestors of 

 the clear-wings had wings like other moths. 



In all the foregoing instances the mimicking insects 

 imitate various members of the Hymenopterous order ; 

 but we have now to notice a case where a moth imitates a 

 bird so completely as to deceive even the best observers 

 when the two creatures are on the wing together. The 

 moths in which this kind of mimicry occurs take their 

 name of humming-bird hawk-moths trom this very cir- 

 cumstance, and are represented by a species not very 

 imcommon in some parts of our own country. So close 

 is the resemblance between these moths and humming- 

 birds that Mr. Bates tells us that, when on the Amazons, 

 he has actually shot specimens of the former in mistake 

 for the latter ; and the natives of these regions are firmly 

 convinced that both are of the same species. The ex- 

 tended proboscis of the moth does duty for the slender 

 beak of the bird, while the end of the body of the former 

 is expanded into a kind of brush which imitates the tail 

 of the bird. Humming-birds are, of course, not seized as 

 prey by insectivorous birds, and hence the moths escape 

 their natural enemies from their resemblance to the 

 humming-birds. In our own country, where there are 

 no humming-birds, it is somewhat diflicult to see what 

 advantage its bird-like form is to the humming-bird hawk- 

 moth, and possibly its comparative rarity may be due to 

 the absence of the birds it mimics. 



We come now to those very remarkable cases of 

 mimicry, as exemplified among the butterflies, where one 

 species mimics one or even more members of the same 

 order, owing to the immunity of the latter from the 

 attacks of birds on account of their unpalatable taste. 

 That the mimicked butterflies are protected by their un- 

 pleasant taste has been amply proved by their being 



offered over and over again to birds, by whom they are as 

 invariably rejected. Their immunity from attack is 

 further proved by their slow flight, and by the bright 

 colouring of the under sides of their wings, so that they 

 have no means of concealing themselves. Most of these 

 mimicked butterflies are found in tropical and sub-tropical 

 regions, and belong to the great families known as 

 DanaiiiUc and HeJiconidie. In America these butterflies 

 are usually mimicked by various species of the family of 

 " whites " [Pi<')->(lit), which, as we all know in the case of 

 our common cabbage butterfly, are eagerly sought by 

 birds ; and the difierence of the mimicking species from 

 an ordinary white by the assumption of the bright colours 

 of the Danaids is so great that nobody but an entomologist 

 would imagine for a moment that it even belonged to the 

 same family. It is, moreover, curious that there is one 

 instance where two species of Heliconids inhabiting adja- 

 cent regions are respectively mimicked by two varieties of 

 one and the same species of " white." 



Stranger even than this, however, is the case of certain 

 South African swallow-tailed butterflies. In this group, 

 as a rule, both sexes are alike, and furnished with the 

 characteristic " tails " ; but in one South African species 

 the females entirely lose their appendages, and alter their 

 coloration and the form of their wings so as to mimic not 

 only one, but actually three distinct species of Danaids. 

 Here, then, we have an instance in which a single species of 

 butterfly exists under four totally distinct forms; viz., the 

 typical swallow-tailed male, and the three varieties of 

 tailless females respectively mimicking the thi-ee Danaids. 

 No one would have the faintest idea that the three females 

 belonged to the same family, let alone to the same genus 

 and species, as the male ; while the three varieties of the 

 female would be assigned without hesitation to as many 

 distinct species. That female butterflies are more often 

 protected by mimicry than the males is a fact which may 

 probably be explained by their extreme importance to the 

 race, and also from the circumstance that when heavily 

 laden with eggs they are more likely to fall a prey to birds 

 than are the lighter males. 



A great deal more might be said on the subject of 

 mimicry in butterflies, but we mast pass on to our last 

 instance of this feature, which is, perhaps, the most 

 peculiar of all. In this case the mimicked insect belongs 

 to that peculiar group of ants which have the curious 

 habit of carrying in their mouth a leaf which extends 

 backwards over their bodies, and apparently acts as a kind 

 of shade. Now, in British Guiana, there is an insect 

 allied to the cicadas and other bugs, in which the leaf 

 borne by these ants is represented by the thin and laterally 

 flattened body of the creature, which is so compressed that 

 it does not exceed a leaf in thickness, while its jagged 

 upper border simulates well enough the irregular contour 

 of the leaf carried by the ants, of which the borders are 

 generally gnawed by the bearers. Although the legs and 

 lower part of the body of this most curious insect are 

 reddish in colour, the leaf-like upper part of the body has 

 assumed a green hue exactly resembling that of the ant- 

 borne leaves. In a drove of cooshie ants, as the leaf-bearers 

 are called, the mimicking insect is distinguishable solely by 

 its somewhat inferior size ; this dift'erence is not, however, 

 sufiiciently great to attract the attention of birds, which 

 have learnt by experience that the cooshies are by no 

 means palatable morsels. 



It would be beyond the scope of the present article to 

 enter upon the difficult question of the means whereby 

 these mimetic resemblances, whether to animate or 

 inanimate objects, have been produced ; but sufficient has 

 been said to show that an amount of interest lies in the 



