24 



Congo, 1903-05, Dr. J. L. Todd writes :— " These flies were caught 

 both near, and far from, water. They sometimes occur in swarms 

 and are often found in houses. They bite freely, are persistent in 

 their attacks, and when crushed emit a pecuhar ' bed-bug Hke ' 

 odour."* 



The preKminary stages are passed in running 

 Life-history. and usually in swiftly-flowing water, and the 



eggs are deposited in a compact layer or gelatinous 

 mass on stones or plants close to the water's edge. The duration 

 of the larval stage in African species has not yet been observed, 

 but in those found in temperate climates this stage lasts for about 

 four weeks in summer. In shape the larva is somewhat cylindrical, 

 broadest posteriorly, where it is attached by means of a terminal 

 sucker to a stone, the stem of a water-plant, a dead leaf or other 

 object. The larva is able to shift its position by crawling in a 

 looping fashion, attaching itself by means of a thoracic proleg 

 situated on the ventral side close behind the head, but usually 

 it remains in a more or less erect attitude. The head is strongly 

 chitinised, brown or blackish in colour and almost quadrangular ; 

 the body consists of twelve segments, from a narrow cleft on the 

 dorsal surface of the last of which are protruded retractile, branched, 

 tracheal gills. The larva feeds on algae, diatoms, and parts of 

 phanerogamous plants, which are brought to the mouth by means 

 of the currents set up by two broad, fan-like 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 

 fujm remains motionless, breathing by means of a pair of branched 

 respiratory processes, which project from behind the head. About 

 a week (in temperate climates at least) is occupied by the pupal 

 stage, and then the perfect insect, making its escape through a rent 

 in the back of the thorax, ascends to the surface in a bubble of air, 



* Annals of Tropical Medicine and Parasitology, Series T.M., Vol. I.. No. I., p. 3(5 

 (February 1, 1007). 



