^»^ 



•■ *• ..'.... \ 



j' j '*** • £+ 



1915.] Fauna of the Chilka Lake : Aquatic Insects, 185 



its apex, but the sexual characters of this limb are not yet apparent. The first seg- 

 ment of the antenna has increased in relative length. 



The third instar (pi. xi, figs. 3, 4) is that described by Distant under the name of 

 Fabatus servus. The sclerites are now well developed, although each is still distinctly 

 divided into two halves and separated from those next it by a membranous inter- 

 space. The tarsus of the first leg is much longer, but still consists of one segment. 

 The tibia exhibits the secondary sexual characters, 

 the large tooth characteristic of the male being well 

 developed. The femur, however, is not yet incrass- 

 ated. One of us has described the colouration of fig. 2.—Euratas formidabilis, Distant, 

 this instar elsewhere ; but we may note that speci- Tarsus of ist leg of 3rd larval instar. 



r showing the two segments of the adult tar- 



mens preserved in spirit give as it were a negative sus within the single larval segment (from 



r . . _ . co-type of " Fabatus servus," Distant): x 30. 



picture of those pinned and dried, the latter preserv- 

 ing to a considerable extent the natural colour of the species (cf. figs. 2 and 3, pi. XI) 



We have mounted one of Distant' s co-types in Canada balsam, after clearing it 

 with caustic potash, but we can find in it no trace of a joint in the tarsus at a level with 

 the claws (see Distant' s fig. loc. cit., p. 156). The specimen was evidently just about to 

 undergo its final ecdysis and the true position of the joint, as it occurs in adults consi- 

 derably behind the base of the claws, can be detected internally (text-fig. 2) . The form of 

 the genital appendages can also be made out, although there is no external trace of them. 



Euratas formidabilis occurs at all times of the year both in the main area and in 

 the outer channel, but is perhaps more abundant in the former than in the latter. It 

 has also been found in backwaters at Vizagapatam and Ennur on the Madras coast and 

 was originally described from the Andamans, where it is common in sheltered bays. 



It was noticed in an aquarium that disturbance of the surface of the water 

 caused both young and adults to dive. They were, however, apparently unable to 

 remain below for long and floated up again immediately in spite of vigorous efforts. 

 In calm weather the adults were seen chiefly in the middle of the lake, as a rule 

 singly or in pairs ; but when the wind was high they congregated among rocks near 

 the edge and in other sheltered spots. The young are markedly gregarious and were, 

 as a rule, found among rocks and weeds. 



The food of the species consists largely of insects that fall or are blown into the 

 water. We have seen several individuals sucking a dead dragon-fly, but small insects 

 are seized by single bugs. Fish-fry that swim on the surface, particularly those of 

 Haplochilus melanostigma, are also eaten. Prey is held not between the femur and 

 tibia of the first legs, but between the inner surfaces of the two femora. 



The male clasps the female with his anterior femora immediately behind her 

 front legs , the spines on the femora assisting in maintaining a hold. It is note- 

 worthy that in Asclepios annandalei L , in which the spine characteristic of the male is 

 situated on the femur instead of on the tibia, the female is gripped much further 

 back, immediately in front of the third pair of legs. 



Distant, Ann. Mag. Nal. Hist. (8) XV, p. 504, text-figs. (1915)- 



