198 Insects most injurious to Cultivators : — 



has been repeatedly observed with other insects which occasion- 

 ally swarm; such as the lady-bird, Galeruca tanaceti {Trans. 

 E7it. Soc.y No. 2.) ; that they are not sufficient to lead to the 

 conclusion, that the insect is not originally a native of this country. 

 It is also completely distributed through the southern parts of 

 England, having been found in Hampshire, and in the neigh- 

 bourhood of Bristol. The periodical appearance of the insects 

 is, in like manner, no proof of their foreign origin ; for it is a 

 circumstance of which the youngest entomologist is aware, that 

 many insects are notoriously periodical ; and, indeed, in one in- 

 stance, the jieriods of the reappearance of an insect (Cicada 

 septendecim) have been recorded to take place at fixed distances 

 of time; namely, seventeen years apart. In the turnip saw-fly, 

 however, it is more probable that it is owing to some peculiar- 

 ities of the weather ; not only of the year when the niggers do 

 the most mischief, but also of the preceding year, and especially 

 of the preceding winter, when the parents of the nigger cater- 

 pillars were not subjected to the ordinarily controlling power of 

 parasites, or other causes of destruction. That they are subject 

 to some such check is evident ; and that one, at least, of these 

 checks is an insect parasite, I have proved by discovering en- 

 closed in one of the cocoons the pupa of a dipterous fly, which 

 had undergone its change within the skin of the nigger, portions 

 of which, greatly stretched, remained on the outside of the dip- 

 terous pupa, as well as the head of the nigger, which remained 

 entire. An analogous instance, in the case of the O'phion Do- 

 sithea, has been recorded by M. Victor Audouin, in the Atmales 

 de la Sociele Entomologique de France for 1834. 



As to the modes adopted for the destruction of the niggers, 

 it has been su<><Tested that it would be advantiigeous to draw a 

 hurdle or something else over the turnips, and to repeat the 

 operation from time to time : this has the effect of brushing 

 them off' the leaves ; and, as it seems they are unable to crawl 

 upon the ground, and recover their station, they must conse- 

 quently perish unless they are full grown at the time. (Curtis.) 

 Messrs. Yarrell and Saunders both mention the good effects of 

 strewing quicklime by broadcast over the ground, and renewing 

 it when dispersed with the wind. Part of a field near Dover is 

 stated by the latter gentleman to have been thus advantageously 

 treated ; but i'ew caterpillars remaining on it, although the neigh- 

 bouring fields suffered greatly. 



Itusticus and W. C. both mention that many enterprising 

 farmers had saved those of their fields where the injury had 

 scarcely begun, by turning in hundreds of ducks, a boy going 

 before them with a long pole to brush the caterpillars for them 

 off the leaves .of the })lants ; and that it was amusing enough to 

 witness the ducks waddling after their courier, and devouring 



