50 MB. J. C. MOTTRAM ON THE 



scanty the fish most often take both insects, no doubt because their general 

 appetite is very good. Neglecting this class of fish, the following figures 

 were obtained : — Number of fish observed 201, fish taking only duns 149, 

 fish taking only black gnat 52. 



Similar observations indicate that the sub-imago of Baetis pumilus, Burm. 

 (" Iron Blue Dun "), is more palatable than B. Unoculatus, Leach (" Pale 

 Watery Dun"), and that the imago of the smaller Ephemeridse is more so 

 than Simidium ("the Reed Smut"). 



Even these observations are not quite free from doubt, the relative 

 prevalence of the insects may play a part, or one insect may be more easily 

 captured than another, or more easily seen. Nevertheless, there is stronger 

 evidence that fish do appreciate a difference in palatability. There are two 

 species of the Ephemeridse, Heptagenia sulfuria, Mull. ("Yellow May Dun'''), 

 and Leptophlebia marginata, Eaton ("Turkey Brown Dun"), which are 

 almost never taken by trout. A " Yellow May Dun " (sulfuria) has never 

 been seen to be taken by a trout, though a great number have been observed 

 floating down where fish were feeding. On two occasions considerable 

 hatches of this insect were seen, but the fish left them alone. 



Obs. — -"Sept. 25, 1909, K. Teme, Eardistone, saw a good hatch of the 'yellow 

 May dun ' (H. sulfuria), many on the water at the same time ; this is rarely seen ; 

 trout and grayling rising at other flies, but no fish feeding on the ' May dun.' 



" Sept. 28, another hatch of the ' yellow May dun ' (sulfuria), fish not taking the 

 insect." 



As regards the " turkey brown " (L. marginata), I have seen this insect 

 taken on one occasion by two fish, one of which was captured and two 

 recovered from the stomach. 



Obs. — " 10. 5. 1914, E. Lambourne, Newbury, a batch of ' turkey browns ' 

 (L marginata), saw two fish take these insects : killed one and recovered two from 

 the fish's stomach ; this is the first time I have seen this insect taken by fish." 



It is the expei'ience of anglers that these insects are very rarely taken. 

 These two insects are among the less common species of the Ephemeridse, 

 and it is possible that their scarcity may be a factor in causing them to be 

 neglected by the fish ; on the other hand, fish are often seen feeding on 

 other species even when the hatch is very sparse. 



There are two other insects which are almost immune from the attacks of 

 trout, Gerris thoracica, Fabr., and Velia currens, Latr. ("water-skaters"). 

 In the vast majority of trout-streams these insects abound, but I have never 

 seen one taken by a fish ; on two occasions I have recovered single specimens 

 from the stomach. The taking of these insects has been observed hy anglers 

 on a few occasions. It is possible the fish neglect them because they are 

 difficult to capture ; they are very active, buoyant, and difficult to drown, 



