58 



The Natuealtst. 



functions decreasing in power with the increase of the cold. Still, even 

 if totally frozen, many kinds of caterpillars are not injured so long as the 

 freezing takes place in the shelters they have made for themselves. In 

 the earth-cells, in which many kinds of caterpillars or grubs pass the 

 winter, they are protected from drying winds and sudden changes of 

 temperature, and these cells also appear to exclude the wet, so that the 

 caterpillar lies clean and dry within, without risk of its breathing pores 

 being choked by mud, which, though possibly not of importance to it 

 while torpid, is a very serious matter when it wakes from its wintry sleep. 

 It appears, in fact, that so long as they are in their own cells these 

 common farm pests will survive a greater amount of cold than is likely to 

 occur in these islands. If they are not in their own cells, 'circumstances 

 will affect them very differently : and if, by ploughing, digging, or any 

 other operation, the caterpillars and chrysalids can be thrown out of their 

 cells or other wintry defences, and scattering xhem, mixing them with the 

 soil and exposing them to drying winds, to alternate freezing and thawing, 

 or to lying soddeningin the rain or wet ground, when too torpid to move, 

 that thus great numbers are got rid of. Thus, in the case of ihe maggots 

 and pupae of some kinds of the diptera (or two-winged flies) we may throw 

 them on the surface, or turn them down so deeply in autumn cultivation, 

 that any flies that may develop will have no power to work their way 

 through the quantity of earth above them ; and the best known remedy 

 for the wheat midge is the method in which this plan is carried out in 

 Canada and the United States of America. This is, when the " red 

 maggot " is lying at the bottom of the stubble or a little below the surface 

 in autumn, to skim off with the first turn-furrow of the plough about two 

 inches of the surface-soil, with all the stubble, weeds, and vermin in it, 

 and turn it to the bottom of the furrow ; then raise another slice with 

 the second turn-furrow, and throwing it over the first, bury it some 

 inches deep. T3y this means the pest may be got rid of, if the surface can 

 be left undisturbed until after the natural time of development for the 

 wheat midge in ihe following season has passed ; for even if these gnat- 

 flies develop, their delicate powers are quite unsuited for piercing through 

 the firm ground above them, and consequently they perish. It is, how- 

 ever, necessary that the ground should not be turned up again too soon, 

 or the chrysalids or maggots in their cases may develop, and we shall have 

 no benefit from their temporary burial. In the case of saw-flies, the 

 cocoons may be thrown out in scores from under gooseberry bushes ; in 

 masses as large as a man's fist from under the pine-trees they have infested 

 in autumn ; and, in the case of beetle larvae or chrysalids, we may get rid 

 of some very injurious ones in this way ; but the wire worm, having the 

 instinct to bury itseK when the weather is too cold for feeding, can only 

 occasionally be dealt with in a torpid state ; and the cockchafer-grubs, 

 which are a great pest, also bury themselves safely too deep to be easily 

 reached. In many cases the egg, whether laid singly or in clusters, is so 

 placed as to be protected from rapid drying or sudden changes of temper- 



