ON THE BRITISH SPECIES OF SIMULIUM — II. 237 



Habitat. — ^Weedy rivers with only a moderate current, usually associated with 

 S. argyreatum and sometimes also S. ornatum, on various water-plants, to a depth 

 of 6-9 inches, the larvae mainly on the lower or down-stream side of the leaves, 

 the pupae mainly on the upper or up-stream side. 



Breeding Season. — There are probably three main broods in the year, in March or 

 April, July and September. No evidence has so far been obtainable as to the 

 method of over-wintering, the earliest date on which larvae or pupae have been 

 collected being 7th April, and the latest 10th September. Females, however, have 

 been captured on the wing as early as February, and specimens of both sexes, 

 obviously newly hatched, at the beginning of April. 



Oviposition. — Mr. H. Britten has given (Ent. Mo. Mag. May 1915) some interesting 

 notes on the oviposition of this species, and in May 1919 I was able to confirm his 

 observations, watching the females enter the water for the purpose of laying their 

 eggs. In this case the eggs were deposited on a dead wiUow branch which was 

 lodged in the river Ivel near Sandy, Beds, The insects chose a spot which was 

 entirely sheltered from the current in order to enter the water, walked in to a depth 

 of several inches and laid their eggs on the lower side of the branch. As Newstead 

 noticed in the case of S. ornatum, the wings were wrapped round the abdomen and 

 confined a layer of air between them and the body. Oviposition completed, the insect 

 walked to the down-stream side of the branch, let go its hold and rose to the surface 

 in its bubble of air. Some specimens took to flight the moment they reached the 

 surface, others floated on the water for a few seconds before being able to rise. 



The eggs of S. equinum are not, like thos^of other species, enclosed in a hard 

 gummy matrix, but in soft jelly hke those of many Chironomidae. They are 

 however placed close together in a single layer. 



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

 R. Misbourne, near Denham, 10.ix.15 ; K Colne, near Denham, and stream in 

 Denha'm village, 26.viii.15, larvae of all sizes and pupae, chiefly on water-plants, 

 a few on stones. Herts. : R. Chess, near Chorley Wood, 30. viii. 15, immature 

 larvae; River Lea at Hatfield, v. 1916, on Ranunculus] River Ivel at Radwell, 

 various dates. Cambs. : River Granta at Hauxton, 5.vii.l5, in immense numbers 

 on Scirpus and Potamogeton ; also at Shelf ord, l.vii.l5 and v. 17, and Grantchester, 

 28.iv.16, on Ranunculus; Hauxton, 7.iv.l7, numerous pupae and some larvae in 

 one patch only on sedge at side of river. Suffolk : River Lark, near Mildenhall, 

 25.iv.16, on Ranunculus, etc. ; numerous ^(J hovering in shade, but scarcely any 

 5 $ seen on the wing, and none bit. Hants. : Bournemouth (Z). J. H. Ashworth) ; 

 River Test {M. E. Mosely). Devonshire : In small numbers in the River Otter at 

 Tipton St. John and in the River Sid at Sidmouth, mostly on water-plants, a few 

 on stones. 



Variation — None noticed in larvae. In the pupae the minute spines on the 

 surface of the respiratory organs are sometimes absent. The adults of the spring 

 brood appear to be decidedly larger than those of the subsequent broods ; there is 

 also much variation in the colour of the thoracic and abdominal pubescence of the 

 females, some specimens being much more golden than others ; possibly the spring 

 brood might be distinguishable by being on the average less brightly coloured. The 

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