ON THE BRITISH SPECIES OF SIMULIUM — II. 215 



Blood- sucking Habits. — ^In my previous contribution I stated that some of our 

 •commonest species were probably not bloodsuckers, but this opinion lias since 

 proved to be quite erroneous, as I have had abundant evidence thac both S. ornatiim 

 -and S. lati'pes will attack man ; and though there are still species (such as S. aureum) 

 against which there is no evidence, it will probably be safe to assume that all the 

 species may on occasion develop this habit. It would seem that their blood-sucking 

 propensity depends much more on the weather than on the particular species ; 

 a, still, warm and sunny afternoon in April or May, and perhaps to a somewhat less 

 extent later in the year, will always rouse them to activity. Some further details 

 on this subject are given in the sequel. 



Range of Flight. — ^It has often been observed that Simulium may be found at 

 considerable distances from their breeding places, and though this may in part be 

 due to some stream having dried up and so been overlooked by the observer, yet it 

 is certain that these insects can fly long distances. I have frequently taken 

 S. ornatum and other species at a distance of a mile from the nearest possible breeding 

 place, while on one occasion I took S. venustum on Birds Hill, near Clothall, Herts., 

 two miles from its home in the river Ivel. This power of flight is not by any means 

 confined to females in search of food, as most of my records of specimens taken far 

 from their breeding haunts are of small swarms of males. 



Parasites and Associates. — E. H. Strickland* has desciibed in detail three parasites 

 of Simulium larvae in North America : a worm of the genus Mermis, the sporozoans 

 Glugea spp., and an undetermined Gregarine. I have found what appear to be these 

 same parasites in various species in this country, though the parasitised specimens 

 are never in very large numbers, Mermis in particular being rarely met with. As 

 observed by Strickland, parasitised individuals are generally much above the 

 average size. * 



It may also be of interest to note that small Chironomid larvae are frequently 

 found within the cocoons, particularly of S. ornatum. I believe these are the larvae 

 of a small species of Orthocladius, the cocoons of which are often to be seen lying 

 close against the side of a Simulium cocoon. Whether the Chironomid is dependent 

 upon the Simulium or whether it also occurs away from them I have not been able 

 to ascertain. 



Simulium as Food for Fish. — From the immense numbers in which larvae and 

 pupae of Simulium occur in many rivers, it might be imagined that they would form 

 an important part of the diet of fish, but in the case of trout at least this does not 

 «eem to be so. I have examined the stomach-contents of a number of trout obtained 

 by Mr. M. E. Mosely, and found very few Simulium larvae or pupae among them. 

 In so far as the genus was represented at all, it was mostly by adults (chiefly males) 

 of S. ornatum and S. equinum. Mr. Mosely suggests that this would be accounted 

 for by the habits of the trout, which feeds mostly at the surface or by suction from 

 the bottom. The adult flies found would be those which had fallen into the water ; 

 ^mong these, males from dancing swarms would no doubt be in excess. As noted 

 below under S. tredecimatum, one case has been observed in which large numbers 

 of Simulium larvae were found in the stomach of a trout. 



* Jl. Morph., Philadelphia, xxiv, 191.S, pp. 43-105. 



