ON THE BRITISH SPECIES OF SIMULIUM II. 235 



Breeding Season. — The larvae of the first brood become full-fed about the end of 

 March, the flies appearing early in April, or possibly in March in some cases. 

 Development must be rapid after this as second-brood specimens have been taken 

 as early as the 25th April. On the other hand, first brood specimens have been taken 

 as late as 9th May {A. H. Hanim). The main second brood, however, appears at 

 the end of June, and seems to be the most numerous in individuals. There is 

 certainly also a third and perhaps a fourth brood. I have so far been unable to 

 discover the species in any stage in the winter. The oviposition has not been 

 observed. 



Material collected. — Larvae and pupae have been collected as follows : — Canibs. : 

 River Granta at Hauxton, 5.vii. 15, on Scirpus lacustris ; 7.iv.l7, on sedge at river's 

 edge; Shelford, i.vii.15. Suffolk: River Lark, near Mildenhall, 30.ix.l5 and 

 25.iv.16, on Ranunculus and Sparganium. Herts. : River Ivel near Radwell. 

 Beds. : Cardington MiU, 28.vi.15, on leaves of Scirpus and Sparganium. Hants. : 

 River Test {M. E. Mosely). Mr. H. Garnett has also sent me specimens taken near 

 Evesham flying in clouds over the River Avon, in which thousands of Siyyiulium 

 larvae were living. 



Variation. — None has been detected in the larvae or pupae, but for the reasons 

 stated in the introduction I have come to the conclusion that these are two well- 

 marked seasonal forms of the adult, the first representing the spring brood, the 

 second the subsequent broods. These can be distinguished as follows : — 



Spring form (var. sericatum)"^ : Length of body 3-3 '5 mm. Markings of male 

 thorax not silvery, only dull greyish ; the two patches towards the front of the 

 mesonotum are produced backwards as two rather narrow lines as far as the scutellum 

 and the thorax might therefore be described as greyish with three broad black 

 stripes. Female thorax only moderately shining ; when viewed from in front it 

 shows fairly evident traces of two longitudinal greyish stripes. Front coxae of 

 female black, grey-dusted. 



Summer and autumn form {argyreatum) : Length of body 2-2 '5 mm. Markings 

 of male thorax silvery, especially when viewed from in front, consisting of a pair of 

 more or less triangular patches, wdth their apices directed backwards. Female 

 thorax rather brightly shining, without a trace of longitudinal stripes. Front 

 coxae of female reddish, grey-dusted. 



Blood-sucking. — Further experience only confirms the view that this species is a 

 habitual blood-sucker. At Mildenhall, 25.iv.16, it was in great numbers and very 

 troublesome to a distance of quite half a mile from its breeding place, biting both 

 head and hands. Though, to judge from the relative abundance of pupae, this 

 species was much less numerous than S. ornatum, by far the greater proportion of 

 the bites were inflicted by it, and I also noticed that >S. argyreatmn commenced its 

 attacks much earUer than did S. ornatum. Other records were obtained in the 

 Letchworth district, e.g., 18.iv.l919, bites on hand and ear. These w^ere chiefly if 

 not all of the spring form, but Mr. A. H. Hamm has provided me with several records 

 of the summer form biting in the Oxford district (23.ix.16, 6.vi.l7). 



* M. Seguy notes in regard to Meigeu's type of 8. sericatum, " Detruit, le debris qui 

 reste repoud bien a votre description $." He also states that the types of 8. argyreatum 

 and some others '' repondent bien a vos tableaux." 



