• FAMILY SIMULIID.E THE BLACK FLIES 65 



In Central America three species of Swiulium have been shown to 

 carry a disease disphiying various symptoms and sometimes resulting 

 in blindness. Tlie causative agent is related to the form described 

 above and was named Onchocerca cmcutinis by Brumpt. In some cases 

 of infection there are no clinical symptoms but in others there are 

 erysipelas-like swellings, the name coastal erysipelas being applied to 

 the disease in such cases. Nodular swellings may occur on the head, 

 shoulder blades, ribs iliac crests, etc. In the eye the microfilariae may 

 cause conjunctivitis, Jicratitis and iritis, blindness sometimes resulting. 



Both the fly and man are necessary for the development of the 

 disease. After being ingested by the fly the microfilariae pass from 

 the intestine to the muscles of the thorax where further development 

 takes place. The infective stages occur in the proboscis of the fly and 

 are transferred to man during feeding by the insect. Strong has 

 discussed Onchocerciasis in Guatemala.* 



The larvffi live in streams w-here they attach themselves to stones, 

 l)lants, etc. and collect their food from the flowing water. Pupation 

 takes place wdthin the larval cocoon, the adults emerging under water 

 and, quickly reaching the surface, fly away. Under favorable condi- 

 tions many thousands of larvce may be found together, being so numer- 

 ous as to entirely conceal the surface to which they are attached. 



The latest revision of the North American species is by Dyar and 

 Shannon. t Unfortunately these authors apparently took greater pains 

 to find fault with the work of others than to clarify their own con- 

 clusions and only a study of their material and amplification of the 

 descriptions will result in a clear understanding of the specific limits. 

 In some cases the drawings were evidently made from freshly prepared 

 slides and these show characters which gradually disappear, with the 

 result that the same characters cannot be found in old slides and may 

 not even be present in freshly prepared ones made from old specimens. 

 Just what effect this will have on the validity of several of the forms 

 recognized by the authors it is impossible to say. Malloch:}: has also 

 revised the familv : the two contributions should l)e used together. 



* 1931, Science. N. S.. Ixxiii, pp. 593-594. 



t 1927, Dyar and Shannon, Proc. U. S. N. M., Ixix. Art. 10, pp. 1-54, 7 plates. 



t 1914, Malloch, Bull. U. S. Dept. of Agric. Bur. Ent., Tech. Ser., No. 26. 



