ON INDIAN PARASITIC FLIES. 375 
It has a small retractile head with well-developed mouthparts, pa- 
pillate antennae and no eyes. When full fed it pupates where it lies 
and turns into a mummy-like pupa often with strong spines on the 
head and anterior parts. These spines are appliances developed in 
connection with the larva’s parasitic life to enable the imago to reach 
the open air. 
Most of what is known as to the parasitic habits ot these 
flies we owe to the French entomologist Fabre. Argyrameba 
Sch. is a widely distributed genus with thirteen India species. Fabre’s 
account relates to A. trifasciata Mg. which is parasitic on larval 
masonbees. These bees (Chalicodoma) make mud nests on walls 
and roofs. The parent Bombyliid drops an egg on the nest whilst 
hovering over it. From this an extremely minute and slender larva 
is hatched. For a fortnight it remains quiescent and fasting. Then 
it shows unexpected endurance for one that has fasted so long and 
amazing pertinacity in seeking a way into the chamber where the larva 
mason-bee is lying. The Bombyliid larva has a deflexed horny 
head with stiff bristles. Four pairs of long setae serve as organs 
of locomotion. By dint of searching it discovers some crack in 
the masonry through whch it can insinuate its small body. 
Fabre likens this persistence to the root of a plant working its 
way through a wall to seek nourishment. This primary form of 
the larva enables the parasite to reach its victim. Once within 
reach of food it grows, becomes obese and the setae disappear. 
The parasite feeds on the host, without killing it, by applying a de- 
licate sucker-like mouth to different parts of the body in turn. At 
the end of 12 or 15 days the parasite is full grown and the host is re- 
duced to an empty shell. For some months the larva remains qui- 
escent and in the followmg spring it pupates. Then comes the crisis, 
for the Bombyliid fly must reach the outer world. Neither the 
larva, nor the imago has organs capable of doing the work of 
excavation which is needed and the haircrack which admitted the 
fasting larva will not permit an exit to the full-fed animal. The 
Bombyliid pupa, however, has the necessary appliances: (a) 
on the anterior part, spines (b) on the middle segments, rigid hairs 
directed backwards (c) on the posterior part, horns. The pupa as a 
whole is curved into a crescent; and having fixed itself in a firm 
position by the posterior horns it digs a gallery, by which it can escape, 
using the head-spines as picks. The pupal skin bursts when an exit 
has been effected; the fly emerges leaving the skin sticking in the 
mouth of the gallery. 
Bombylius I. is a large genus with a world-wide distribution. This 
genus is parasitic on small bees (Andrena and Halictus and others) 
which live in colonies in sand banks. From India ten species have 
been collected. B. major L. is not at all uncommon on the Simla 
hills and B. orientalis Macq. is found all over India. B. major has 
