29 



It feeds on algns, diatoms, and parts of phanerogamous plants, which 

 are brought to the mouth by means of the currents set up by two 

 broad fan-Hke organs situated upon the head. In colour the larva 

 varies according to the species, and perhaps also to some extent in 

 accordance with its food, from deep shining black to yellow or dark 

 green. When mature, the larva spins a silken cocoon within which 

 it pupates, and in which the pupa remains motionless, breathing by 

 means of a pair of branched respiratory filaments, which project 

 from behind the head. The pupal stage lasts for about a week, and 

 the perfect insect, making its escaj^e through a rent in the back of 

 the thorax, ascends to the surface in a bubble of air, and makes its 

 way to the stem of a rush or some similar support on which it rests 

 until its tissues are sufficienth' hardened to enable it to fl\-. 



Genus 

 SIMULIUM, Latreille. 



Simulium reptans, Linn. 

 Plate lo. 



So far as present experience goes, this would appear to be 

 essentially a northern species, since all the British specimens of it 

 in the Museum collection come from beyond the Tweed. A very 

 similar species, which is common in the midland and southern 

 counties of England, is distinguished from 5. reptatis by the middle 

 tibia; of the male being wholly brown, or, at any rate, not con- 

 spicuously silvery-yellow at the base, and by the hind tarsi in the 

 female being less clear yellow on the basal two-thirds. Well- 

 preserved females of ^. reptans show on the anterior half of the 

 thorax a whitish-gre}' blotch on each side above the anterior angles, 

 which unfortunately does not appear in the plate ; besides this, the 

 thorax is clothed with a closel}--fitting coat of minute golden hairs, 

 the tibia;, with the exception of the tips, are in reality conspicuously 



