78 TWELFTH REPORT. 



tached near its njt-str-eani border. Tliev were found quite uniforinly 

 near the water's surface and none were taken at a greater distance than 

 ten inches below the surface. When found as far as ten inches from 

 the surface their support was a stick which slanted into deeper water 

 below them. 



Light did not appear to have intluenced the female in selecting- the 

 place for depositing the e^^, so that larvae were commonly found in 

 sun-lit places, but also in darkness. Thus water was often heard gurg- 

 ling undergTound over the roots of stumps in the cedar swamps ad- 

 jacent to Carp Creek. In one such case the overlying moss and earth 

 was removed to reach the water and a larva was found in it. The 

 nearest opening to the surface was about two feet distant. Temperature 

 of the water appears to have little influence in determining the location 

 of the eggs or larvae. Larvae were found in water of 10° C. and in 

 that of 251/2° C. In the laboratory the larvae were found to endure 

 for six hours temperatures of 31° C. to 35° C. 



No larvae were found in the still pools of streams nor in the lakes. 

 Probably they are unable to obtain food with their fan-like mouth parts 

 except in ra])id water. 



The conditions necessary for the breeding of the flies thus appear to 

 be rapid water and a smooth surface for the attachment of the larvae. 

 All the conditions of light and temperature obtaining in this region ap- 

 pear to be suitable. 



Tlie reYhedp: "^arp Creek and the other small streams flowing south 

 from the ridge near which the Biological Station is located, run through 

 sand and transport sand. Sand forms the banks and beds of these 

 streams, and the logs and branches obstructing the stream soon become 

 coated with it. Only the leaves, pieces of bark, logs and twigs that lie 

 near the surface of the water and chiefly the lower, smooth surfaces of 

 these are free from sand. Either the adult black flies do not attach their 

 eggs to the sand-covered surfaces, or the larvae are unable to retain 

 their hold on them, or the sand shifts and eggs and larvae are swept 

 down stream. In any case the eggs and larvae are found attached only 

 to the smooth sand-fr-ee surfaces and these lie near the surface of the 

 ■vyater. To remove the twigs, branches, logs and lodged leaves that ex- 

 pose smooth surfaces free from sand would destroy the black fly larvae 

 and make the stream unsuited for the breeding of black flies. 



To determine Avhether larvae would be killed by removal from the 

 stream or Avould make their way back to it, leaves with attached larvae 

 were placed on land and the movements of the larvae watched. They 

 were found to go to the lower parts of the leaves or to get between their 

 moist surfaces. None of them moved more than two inches from the 

 places to which they had been attached. Twenty-four larvae were 

 watched; all were dead within forty minutes. Less than ten minutes on 

 a dry surface sufficed to kill the larvae. Hence to remove from the 

 stream the smooth ohjeefs to u-hich the larvae are attached should 

 great] II lessen, the hlael: flij pest. 



It is evident that this method is available only in those streams in 

 which silt or sand covers the bottom, but is of no value in shallow, 

 stony strean)S. In such streams the use of heavy oil or the damming of 

 the streams has been found efl'ective. 



Manistee. Mich., Apr. 1010. 



