iioS 



THE NATURE BOOK 



ABOVE ARE TWO CATERPILLARS ALMOST READY TO 

 BECOME CHRYSALIDES. BELOW, ON THE RIGHT, 

 IS THE COMPLETED CHRYSALIS. 

 ON THE LEFT APPEAR THREE 

 CHRYSALIDES OF THE PARASITIC 

 TACHINA FLY. 



In favourable weather, at the 

 end of from three to four weeks, 

 the moth is ready to appear, 

 bursting its chrysaUs skin and the 

 silken threads of its cocoon, and 

 appearing upon the branches to 

 shake out the folds from its wings 

 (p. 1 109). It does not follow, how- 

 ever, that such a successful issue 

 always takes place, as the experi- 

 ment previously referred to made- 

 clear. 



It was obvious that something 

 was amiss in the cocoon in whicli 

 the three small pup?e appeared. In 

 several other exam])les under ob- 

 servation the same thing occurred, 

 and, after seventeen or eighteen 

 days, from each of these little 

 chrysalides there emerged what 

 appeared to be a common house- 

 fly. A closer glance at these insects 

 revealed the fact that although 

 they closely resembled house-flies, 

 yet they were really only near rela- 

 tives of those famihar insects : a 



species, indeed, whose habits are 

 very different. 



These flies belong to the family 

 Tachinidce, and are commonly re- 

 ferred to as Tachina flies. There 

 are numerous species, most of 

 which in general appearance re- 

 semble house-flies, or blow-flies. 

 To man they are most beneficial, 

 as in the larva stage they prey 

 largely upon caterpillars which 

 feed upon his crops. 



Whenever a gooseberry, cur- 

 rant, sloe, or other bush, on which 

 numerous caterpillars are seen to 

 be feeding, is surrounded by a 

 buzzing swarm of flies, some of 

 which are continually aUghting 

 and moving amongst the leaves, 

 it will be found that these are 

 Tachina flies. Their function is 

 to seek out plump-bodied cater- 

 pillars, and, by means of a gummy 

 substance, to fasten their eggs to 

 the skins of the larvae. From 



THE PARASITIC ICHNEUMON FLY SEEKING FOR 

 CATERPILLARS. 



