264 MK. E. SHELFORD OX MIMETIC IXSECTS AJsD [NoV. 4, 



also made use of by several species of Calohata 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 with a black band at the apex of the 

 femora and tibite. 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. M.vmic.'^. Xylojjhag us s^. (Fam. Leptida?.) Plate XXII. fig. 8. 

 Model. Mesostenus sp. Plate XXII. 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 antennfe 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 extra- 

 ordinary features. 



viii. Mimic. Sepedon sp. near javanicus (Desv.). (Fam. Scio- 

 myzidfe.) Plate XXII. fig. 4. 

 Model. Collyris emai^ginata (Macl.). Plate XXII. fig. 3. 



It is not usual to find amongst the Diptera species which 

 mimic any other order of insects than the Hymenoptera. This 

 example and a species of Celyphus, which only very doubtfully 

 can be considered as mimicking a small bug, are the only cases 

 known to me. 



Both of the species now 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.). 



