122 CULTURE OF FARM CROPS. 



The length of the caterpillar is about one-twelfth of an 

 inch ; it has no legs ; the colour is a citron yellow. When, 

 about to pass into the chrysalis or pupa condition, it spins 

 itself a fine transparent web, and which is attached to a sound 

 grain or to the inside of one of the scales of the chaff. 

 Seeing, as Professor Henslow suggestively remarks, that 

 " there is a strange economy in the insect tribe, by which 

 particular species in certain seasons favourable to their 

 production are enormously multiplied," it does seem worth 

 the attention of farmers to consider how best the increase 

 of the wheat midge may be prevented. As the chrysalides 

 of this insect remain attached to the chaff scales during 

 the winter, it appears at first sight the best plan to burn 

 the chaff ; or to scald it for food after the grain has been 

 thrashed out. But it appears that in some cases the cat- 

 erpillars drop from the chaff scales to the ground before 

 the crop is removed, and burying themselves in the soil, 

 are, it is presumed, changed to chrysalides, and remain 

 buried till they are finally changed into the midge. In 

 this latter case,. one authority presumes that the caterpillars 

 must have been ichneumonized before they could have 

 their habits so changed. By this term is meant that the 

 caterpillars have been attacked by one of the tribe of in- 

 sects called ichneumons, which lay their eggs in the bodies 

 of other insects, usually while these latter are in the cater- 

 pillar state. The eggs being hatched in this strange re- 

 ceptacle produce caterpillars which devour the non-vital 

 parts of their living conveyance, which thus dies, or is 

 passed, before it is finally destroyed, into the chrysalis stage. 

 The caterpillar of the ichneumon also passes to the chry- 

 salis state, and which remains in the body of its victim, 

 or issues out of it before passing to the chrysalis state. The 

 caterpillar of the wheat midge has " certainly one, and pro- 

 bably not less than three distinct species of these ichneu- 

 mons appointed to keep it in check." The most active of 

 these the Platygaster Tritici, ichneumon flies or midges 

 a black four-winged insect with a sharp-pointed tail 

 may be seen in the months of July and August flying 



