37 



occur anywhere and everywhere ; they have been found in the 

 tobacco refuse of an American spittoon, in hot salt springs, in water, 

 in earth, mining leaves, in decaying wood, in fungi, and in filth of 

 all kinds. They are found in the nests of bees and ants, well known 

 as parasites on lepidopterous larvae, less well known perhaps as 

 parasites on Hemiptera and Hymenoptera. The ox, horse, ass, sheep, 

 and red-deer suffer from the larvae of the bot-fiies {(Estridce), and in 

 Africa there is a Muscid fly whose larvae are parasitic on dogs, 

 monkeys, and men. Fabre* has given a most interesting account of 

 the life-history of one of the species of the genus Anthrax, whose 

 larvae are parasitic on those of the mason bee. The eggs are laid on 

 the ground in the neighbourhood of the cemented cells of the bee. 

 The larva when newly hatched has the form of a hair-like worm. It 

 can exist seemingly without nourishment, and endeavours to attain 

 the interior of the bee's cell through some minute crack or crevice 

 in the protecting masonry. When one has succeeded it completely 

 changes its form, and appears in the next stage as a grub or maggot 

 with a sucker-like mouth, with which it absorbs the contents of the 

 body of the unfortunate bee-larva without injury to the delicate skin 

 of the latter. A further change to the pupal condition turns this 

 feeble grub into a robust creature, with a well-developed head armed 

 with thorny spines, and having the body circled with rings of strong, 

 backward-pointing bristles. With its armed head it breaks its way 

 through the cement walls of the cell, the backward-pointing bristles 

 preventing it from slipping back in the tunnel it makes for itself, and 

 finally there emerges from this spined and bristle-bearing pupa the 

 perfect insect, making the fifth form from the egg state, a particularly 

 fragile-looking fly which Fabre compares to " a morsel of down 

 almost as fragile as a snowflake." I should like here, though not 

 bearing on the subject of this paper, to testify to the great pleasure 

 I have experienced in reading the works of the great French 

 naturalist Fabre, of whose studies in natural history (/. e. the life- 

 histories and habits of insects, apart from the classification of speci- 

 mens) Darwin t wrote, "Never have the wonderful habits of insects 

 been more vividly described, and it is almost as good to read about 

 them as to see them." 



Many of the non-parasitic dipterous larvae are of predacious 

 habits. Syrphid larvae prey on Aphides, and there are several 

 instances recorded of their attacking lepidopterous larvae. Dr. Chap- 

 man J has described the case of a Syrphid larva which preys on the 

 larvae of Tortrices of semi-gregarious habits ; and there are records 

 of dipterous larvae preying on those of Coleoptera, Hemiptera, and 

 Hymenoptera. In the family Cecidomyidce the phenomenon of 

 pseudo-genesis occurs, certain Cecidomyid larvae themselves pro- 

 ducing other larvae. This unusual state continues for several genera- 



* J. H. Fabre, " Souvenirs Entomologiques," vol. Hi. 

 t " Life and Letters of Charles Darwin," vol. iii, p. 220. 

 X " Ent. Mo. Mag.," July, 1905, and January, 1906. 



