OCR Text |
Show 1897.] BUTTERFLIES OF THE GENUS TERACOLUS. 5 21 occur in the South-African subregion (the northern boundaries which are the Zambesi E. and Cunene R. on the East and West Coast respectively) and 5 of them are restricted to it. In the Oriental region as many as 8 out of the 19 species are not found further east than Arabia. In any attempt to differentiate the species of Teracolus, or indeed of any other genus of Butterflies, two important facts must always be kept in view: firstly, the strong tendency of these insects to develop more or less marked local variations consequent upon tbe different conditions of their environment in different localities ; and secondly, the phenomenon of seasonal dimorphism, owing to which the same species may present a strikingly different appearance at different times of the year, more especially in those countries whose climate is marked by well-defined wet and dry seasons. In dealing with local variation the general rule that I have laid down for myself is, that when two local forms exhibit a gradual mergence into one another so that intergrades occur which might be attributed to either of them, then those two forms constitute a single species. As an example I may refer to T. evagore, Klug. This is a North- African form which is represented in the West and South by the very different looking T. phlegetonla, Boisd. But throughout Central Africa we get the admittedly variable form T. mlnans, Butl., which shows beautifully the gradual change from T. phlegetonla to T. evagore, and I have therefore grouped them together, regarding the latter as a dwarfed and under-coloured climatic variety of the former, to which it is closely linked by a number of other so-called species. On the other hand, in the island of Socotra there is T. nlveus, Butl., which is in every way far more like T. evagore than is T. phlegetonla ; but the slight characters which distinguish it are quite constant (it being confined to the island), and therefore I regard it as a distinct species. With regard to seasonal dimorphism, without a certain amount of field experience it is usually difficult to decide what may be the dry-season form of any given wet-season specimen and vice versa; but the following general rules may give some idea of the seasonal modifications in Teracolus. The dry-season form usually differs from that of the wet-season in the following respects : (a) its smaller size ; there are, however, several species, such as T. faustus, calais, and protractus, in which the dry form is not reduced ; (b) when there is any difference in the shape of the fore wing, that of the dry form is always more acute ; (c) the reduction or complete absence of many of the black markings : in groups like T. achlne and T. evagore this is very noticeable, but apparently it does not hold good in T. Calais,protractus, or chrysonome and their allies, for in them the upperside markings do not vary ; (d) the colouring of the underside of hind wings, which is perhaps the most reliable character of all: the white or green undersides of the wet-season forms assume a yellowish, sandy, or pinkish tinge and become more or less irrorated with fuscous atoms ; the colouring, however, is often very variable in the same species and is |