4 8 SOME SOUTH INDIAN INSECTS, ETC. [CHAP. V. 



small water-bugs (Microvelia), scarcely visible to the naked eye as 

 they run along the surface of the water-film, are able to stridulate 

 so loudh as to be audible from a distance of several yards. The 

 caterpillar of the Death's-head Moth makes a clicking sound 

 when annoyed and the moth itself produces a shrill squeak not 

 unlike that of a bat : but these are defensive sounds rather than 

 communicative. 



I ig. 26.— Hind wing ol male Nyctipao hieroglyphica, showing gland 

 opened ; /. is the frenulum. 



Several moths and a few butterflies are known to stridulate on 

 the winy and such stridulation is doubtless sexual as a rule. As 

 an instance we may quote the case of Nyctipao hieroglyphica, Drury, 

 a large black Noctuid moth which is well known, especially in some 

 ol the Hill-districts of Southern India, from its habit of flying along 

 paths at dusk and producing a loud clicking sound which is often 

 especially disconcerting to horses because the moths seem to be 

 attracted by moving objects and therefore often fly around the 

 heads of horses which may be frightened by the clicking of the 

 moths. The fact that this moth stridulates has been noted before 

 but I am not aware that the mechanism of its stridulatory organs 

 has been examined. In the first place we may note that it is only 

 the male moth which makes a noise and that this is a distinct, loud, 

 sharp click, such as might be produced by running a stout pin or 

 quill slowly but firmly across the teeth of a comb. On examining 

 the moth, a glandular patch covered with long flocculent hair is to 

 n on the upperside of the tore-margin of the hindwing, near 

 the base of the wing, and this appears to be part of the stridulating 

 organ ; it is hollowed and convex on the lower surface of the wing 

 and opens like a purse (being hinged along the fore edge of the 

 wing) and perhaps serves as a sort of sounding-board to increase 

 the noise, which is apparently produced by the tip of the frenulum 

 (the long homy bristle at the base of the foremargin of the hind- 

 wing which locks the wings together in flight): this tip passes 

 through the retinaculum (the loop on underside which holds it in 

 position) and either rubs over the outer surface of the pocket or, 

 more probablj . catches i'^ hinder edge and pulls it open with each 



