Observations on the Turnip Saw- Fly. 



365 



such multitudes of caterpillars might lead to the idea that they 

 had fallen from the clouds ; but when it is well ascertained 

 that every caterpillar must have been produced from a minute 

 egg", which egg must have been laid by a parent fly, it is not 

 possible to reconcile such an idea with their habits and economy;* 

 especially when we recollect that in most instances the caterpillars 

 were at least half grown when discovered, which proved they had 

 been li\dng on something more substantial than air. When we 

 take, however^ a philosophic and more rational view of the subject 

 we shall see that it is quite possible that the parent flies may 

 have been transported to our shores by winds setting in from 

 Norway, Holland, or France, and, after attacking the turnip- 

 crops on our coast, spread themselves over the country, if not in 

 the same year^, in the following season ; and as one female would 

 lay several hundreds of eggs, the rapid increase from myi^iads 

 w^ould be incalculable. 



Fortunately for the farmer the visits of this angel of darkness 

 are few and far between/' otherwise the cultivation of this in- 

 valuable crop would become so uncertain as almost to compel him 

 to abandon its culture. We have seen by a former paper f that 

 the attacks of the turnip -fly are sufficiently vexatious ; but the 

 effects of the black caterpillar are infinitely worse, because the 

 crop is destroyed after all the labour and expense attending its 

 cultivation have been bestowed upon it, and generally at a period 

 so advanced that it is in vain to attempt to repair the loss bv dili- 

 gence or industry. The only remedy is importation ; and it is 

 stated that, when they last appeared, many ship- loads of turnips 

 were transmitted from the continent to supply the deficiency along 

 our coasts. 



As it will be curious and interesting to take a retrospective 

 view of the records of various writers regarding this insect, and 

 useful in future investigations to watch the periods of its appear- 

 ance, I shall now proceed chronologically with its historv. In 

 17S2, Mr. jNIarshall, whose observations are recorded with great 

 accuracy, and with a truly philosophic spirit, stated that in July 

 of that year the turnips at South Reps, in Norfolk, situated about 

 three miles from the sea, which looked remarkably well after a 

 moist spring and fine weather, were observed to be covered with 

 the saw-flies in such numbers that they were like flights of bees ; 

 and it was found that they had already traversed the coast, as the 

 imder-sides of the leaves swarmed with young caterpillars, so 



* It seems to be well attested that aquatic animals, as fish and frogs, have 

 fallen from the clouds with rain ; but such occurrences are very rare and 

 extremely partial ; and that the negro caterpillar should always fall in tur- 

 nip-fields would be very extraordinary. 



t Journ. of Royal Agr. Soc.,vol. ii. p. 193. 



