REPORT OF COMMISSIONER OF FISH AND FISHERIES. 59 



tendent of the Green Lake Station reported the presence of the larvae 

 of two insects in the hatching troughs, and the destruction thereby of 

 some newly-hatched landlocked salmon. Specimens were forwarded 

 to the office of the Commission and were referred to the Department of 

 Agriculture for identification. The following correspondence relates to 

 the subject: 



Green Lake, Me., May 7, 1894. 

 I send by to-day's mail two specimens of water life which made its appearance in 

 large numbers in our troughs just about the time the salmou were hatching or when 

 the water reached 46° F. * * * The large specimens I would say were from five 

 to six days old, while the small ones are not over two days old. The former are 

 full grown. It seems they do not grow to any size, but their development is very 

 rapid. * * * Any considerable number of them in a hatching trough in one 

 night will spin the trough almost full of a very fine web; it is quite strong, too. 

 They will sometimes spin a web around the neck of a fish and choke it to death; 

 then they congregate in numbers and will eat the entire fish if left alone. They 

 also attack the sac of the fish, and this is always fatal, as the sac soon bursts. 

 They would not be able to harm the fish after they are ten days old, but should they 

 come in numbers at the pi-oper time they would destroy a good many fish if not kept 

 out. I have no doubt this same insect will make excellent food for the fry a mouth 



later. 



E. M. Robinson, Superintendent. 



Department of Agriculture, 



Office of Assistant Secretary, 



Washington, D. C, May 19, 1S94. 



Sir: I have the honor to acknowledge the receipt of your favor of May 12, trans- 

 mitting vials containing larvae received from the fish-cultural station at Green Lake, 

 Me., and to report that they have been referred to the entomologist, who submits the 

 following statement: 



" The large larv;e sent by Colonel McDonald are predaceous in their habits. They 

 belong to the species known as Eydropsyche phalerala, a form which is noted for the 

 fact that it preys almost exclusively on the larva} of the genus Simulium, known in 

 different parts of the country as black flies, buffalo gnats, turkey gnats, etc. The 

 smaller larva? sent in a separate vial belong to the genus Simulium; the exact species 

 can not be determined from the larva alone, but it is probably decorum or invenustum, 

 and the adult is the common black fly of the Green Lake region, in all probability. 



"The damage done by the larva' of Simulium in fish hatcheries has been commented 

 upon before. They feed upon aquatic vegetation in part, and in part upon minute 

 infusoria, and the damage to the fish occurs through the spinning of their web 

 through the water, as detailed by Mr. Robinson. The statement that the Simulium 

 larva; cluster upon the young fish after they are caught in the web, and feed upon 

 them, may be doubted. It is very possible, however, that the Hydropsyche larvae 

 will feed upon very small fish captured in the net made by the Simulium larvae. It 

 is a very peculiar and interesting condition of affairs. The best article which has 

 been published on the subject is entitled ' The death web of young trout,' and 

 will be found in volume n of the American Entomologist and Botanist, pages 227- 

 228 (June, 1870). Mr. Seth Green, the well-known pisciculturist of New York, was 

 the first observer to call attention to this interesting habit of the Simulium larvaa. 

 Mr. Robinson is perfectly correct in supposing that the young fry, when they are a 

 little older, will feed upon the Simulium larvse." 



I have the honor to remain, respectfully, yours, 



Ciias. W. Dabney, Jr., 



Hon. M. McDonald, Assistant Secretary. 



Commissioner l'isli and Fisheries. Washington, D. C. 



