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Show 2G4 MR. R. SHELFORD OX MIMETIC IXSECTS AXD [Nov. 4, ;ilso made use of by several species of Calobata and allied genera, but in the case here described the mimicry of an Ichneumon-fly is carried still further, inasmuch as the coloration is almost identical in both species, viz., black with yellow spots on the head and thorax, with alternate yellow bands on the abdomen, while the legs are ochreous w-ith a black band at the apex of the femora and tibiae. Furthermore, the ample clear wings are very similar in both mimic and model (compare figs. 5 & 6, Plate XXII.). The nearest allies of this remarkable fly occur in S. America. vii. Mimic. IXylophagus sp. (Fam. Leptidae.) Plate X X II. fig. 8. Model. Mesostenus sp. Plate X X II. fig. 7. This example is remarkable for the great elongation of the antennae of the fly. In the previous case it was seen that the long antennae of the model were represented by the fore legs of the mimic, but here there is an actual copy produced by means of a very unusual modification amongst the Diptera. The mimicry is so perfect that it will almost bear a close scrutiny through a lens ; the large eyes, prominent clypeus, and maxillary palps of the fly give the head, even when thus closely examined, a characteristic Hymenopterous appearance. For the rest, the coloration is almost identical in both species: black with yellow spots and bands (compare figs. 7 & 8, Plate XXII.). The larva of the fly was found in decayed wood and presented no very extraordinary features. viii. Mimic. Sepedon sp. near javanicus (Desv.). (Fam. Scio-myzidae.) Plate X X II. fig. 4. Model. Collyris emarginata (Macl.). Plate X X II. fig. 3. It is not usual to find amongst the Diptera species which mimic any other order of insects than the Ilymenoptera. This example and a species of Celyphus, which only very doubtfully can be considered as mimicking a small bug, are the only cases knowrn to me. Both of the species nowr under discussion were caught together on the wing on Mt. Serambu, Sarawak, and when seen alive and actively moving about were not readily distinguishable. As cabinet specimens they furnish an instance of the importance of field-work in the study of mimicry, and of the unreliability of dead impaled insects or mere figures unless, indeed, both are prepared with reference to careful observations of the living forms. The fly when alive was of a very brilliant blue like that of the Collyris, but the colour has now faded to a dusky indigo, while the abdomen being much shrunk detracts considerably from the previous resemblance. The legs are brilliant red, and constituted one of the most conspicuous features of both fly and beetle (compare figs. 3 & 4. Plate XXII.). |