206 



Marvels of Insect Life. 



aquatic plants, from which the newly hatched grubs can easily reach the 

 water. These grubs, when large enough to be identified, are rather remarkable 

 creatures, being club-shaped and provided at their hinder extremity with 

 a sucker surrounded by a rosette of minute hooks, by means of which 

 they attach themselves to leaves of water- weeds and stand more or 

 less erectl}', in a cluster. Their limbs have been converted into suckers, 

 the foremost pair united to form a projection on the middle line of the 

 first body-segment behind the head. With the sucker of this they can find their 

 way along threads spun by the mouth, or can double over and take hold of 

 the leaf or stone to which the hinder end is attached. The body is greenish- 

 brown or black, and soft ; but the head is firm, and bears two pairs of pigment- 

 spots which serve as eyes. On each side of the mouth is a lobe bearing about 



fifty filaments, which form a fan. 

 By sweeping the water with these, 

 microscopical food such as diatoms 

 are borne to the mouth and serve 

 for the creature's food. These 

 grubs must be sought for in swift- 

 fiowing streams where there are 

 plenty of water-weeds. 



Before changing to the chr\'sa- 

 lis, the grub spins on the stem of 

 a weed, or on a stone, a slipper- 

 shaped case or socket in which the 

 chrysalis can stand with its head 

 exposed. This chrysalis shows the 

 folded-up wings and antennae of 

 the future fly. On each side of 

 the head is a projection from which 

 spring four long tubes, which 

 branch near their base. These 

 chrysalids are so disposed in their 

 cells that as the weed bends to the 

 current their heads are turned 

 forwards, and the slipper-like case protects them from friction or battering 

 by any solid particles that may be borne by the stream. Just before 

 the fly is about to emerge from the chrysalis its upper part becomes 

 surrounded by air, the skin splits, and the fly emerges into the bubble. 

 The air clings to it and buoys it dry to the surface of the water, over 

 which it walks to land or to the aerial stems of an aquatic plant. This emergence 

 takes place in spring, but there is another emergence in August, the eggs laid 

 in April or May producing a summer brood. 



The flies are said to suck the juices of plants and the sweet excretions of the 

 aphis ; but this possibly is true of the male fly only. De Geer stated that they 

 attacked and sucked the blood of large, smooth caterpillars. It would be interesting 



Photo by] [E. K. Pcanc. 



Pellagra-Fly Escaping from Chrysalis. 



The chrysalis stands in a slipper-shaped case attached to weed or stone, with 

 the head-parts exposed. The flv emerges from the chrysalis into a bubble 

 of air, which clings to it and buoys it to the surface. 



