196 NATURAL HISTORY OF AQUATIC INSECTS CH. 



The pupa-stage lasts for a very few days and then 

 the fly emerges. The larval skin splits across the 

 third and fifth segments, and also along the middle 

 line between these segments. 1 The fly then pushes its 

 way out, and Reaumur tells us that it suffers no in- 

 convenience if it emerges from a floating larval skin. 

 The hairs which cover all parts of its body prevent 

 it from being wetted, and it can stand upon the water 

 as upon solid ground. The deserted larval skin, which 

 served as a cocoon, contains nothing but torn tracheal 

 tubes and the cast lining of the gullet and intestine. 



When the fly first appears its wings are crumpled, 

 but they soon unfold by injection of blood into their 

 veins and of air into their air-tubes. At this time 

 they bleed if cut, which is not the case afterwards. 



The fly has at first sight a Bee-like appearance. 

 Its abdomen is broad and flat, of a full black with 

 yellow patches and spots. The wings when at rest 

 lie one over the other, do not cover the sides of the 

 body, and project beyond it. The antennae are 

 simpler in structure than those of the Blow-fly ; they 

 are commonly described as 3-jointed, but the so- 

 called third joint is long and 5 -ringed, as if formed 

 by the consolidation of as many originally distinct 

 joints. From the back of the thorax two spines 

 stand out towards the abdomen, and hence the name 

 Stratiomys, which means the " armed Fly." The 

 winged Insect haunts flowers, especially heads of 

 Umbellifers, and is most often seen in the neighbour- 

 hood of pools and ditches. 



1 The exact position of the splits seems to vary according to 

 the species. 



