TRANSFORMATIONS OF BUFFALO GNATS. 27 



INSECT ENEMIES AND PARASITES. 



The larvae of Simulium are often parasitized by nematode worms 

 of the genus Mermis, specimens of which have been found by the 

 writer measuring 12 mm. in length. These were found in larvae of 

 S. venustum, coiled around the intestines, and extended from near the 

 caudal end to the thorax. The specimens that attained the greatest 

 length were found singly, but as many as four have been found in 

 individual larvae. According to Strickland (1911), 1 the Mermis 

 retard the development of the pupal and adult histoblasts, cause 

 the death of the larvae, and escape through punctures made in the 

 epidermis. He also states that in the vicinity of Boston, Mass., 

 Mermis was found parasitizing larvae only during the spring, and 

 that there is a seasonal variation of parasitism. The writer, while in 

 South Carolina, found species of Mermis parasitizing larvae from 

 May until late in October, and these larvae seemed to have developed 

 the pupal histoblasts to a much greater extent than is estimated by 

 Strickland. The larvae are also heavily attacked by glugeid and 

 gregarine species of Myxosporidia. 



The writer has found the larvae being attacked by species of 

 Hydropsy che in Illinois and South Carolina. Dr. Howard (1888) 1 

 also mentions this fact in his article on a species of Simulium at 

 Ithaca, N. Y., and gives a fuller account in the Annual Keport of the 

 U. S. Commissioner of Agriculture for 1886, page 510. Species of 

 minnows attack the larvae frequently, and Kiley 2 mentions that the 

 small fishes of the family Cyprinidae also feed on them. 



The pupae, so far as is known, are not parasitized by Mermis or 

 Myxosporidia. The adults have been found by the writer at Spar- 

 tanburg, S. C, to be frequently parasitized by nematode worms of 

 the genus Mermis, which were usually found singly. In one in- 

 stance three of the worms were found in a female S. venustum. 

 The same number were found in a female of S. bracteatum. They 

 were situated in the abdomen, coiled around the Malpighian tubes 

 and intestines, and in some cases extended into the thoracic region. 

 The vitality of these specimens infested by the Mermis seemed to be 

 seriously affected, though they lived for some time, 31 hours being 

 the minimum and 72 the maximum period. All of these specimens 

 thus parasitized were reared from pupae, with 'the exception of one 

 adult female of S. bracteatum, which was taken flying around a lamp 

 at night. No adults taken biting on animals were ever found to 

 contain Mermis. 



1 See Bibliography, p. 35. 



2 Riley, C. V. Report of the Entomologist. In Rept. U. S. Comr. Agr. f. 1886, p. 459- 

 592 (p. 510), 11 pi., 1886. 



