366 



Observations on the Turnip Saw-Fly. 



that in ten days or a fortnight the turnip -plants along the shore 

 were entirely stripped of their leaves. Several days previously 

 the flies had been noticed at Cromer, and Mr. Howse of Over- 

 strand (who lived near the beach, and who was a man of good 

 credit) declared, as well as the fishermen at Beckhithe, that they 

 saw them arrive in clouds so as to darken the air ;" that, 

 fatigued with their flight, they lay upon the cliffs two inches deep, 

 and might have been taken up by shovelsful." * From these 

 circumstances Mr. Marshall considers the flies had come over 

 from the continent ; and fairly calculates that they might be 

 transported from the southern cape of Norway to the coast of 

 Norfolk in ten hours ; and as they can live five or six days with- 

 out food, they could cross from the most eastern confines of 

 Russia, probably, before they were exhausted. Mr. Marshall 

 subsequently remarked that the flies were very wild the third 

 week in August, which he attributed to their being bred in the 

 field ; for those which he had captured three weeks before were 

 not so alert ; and this tends to prove, if it were necessary, that they 

 had visited our shores from foreign countries. 



If the insects take advantage of a gentle breeze lying off the 

 shore in fine warm weather, they would have everything in their 

 favour to depart ; but as it often happens that a certain condition 

 of atmosphere produces the same effects on the opposite coast, the 

 flies would have the wind opposed to them on their arrival, which 

 would account for their falling into the sea, and alighting in such 

 multitudes on the cliffs ; but this I am induced to believe is 

 agreeable to their instinct, as flying against the wind when on 

 land leads them to the plants they are in search of,f Mr. Mil- 

 burn, however, viewing its flights in the turnip-field, says,J " it 

 never flies far ; and thus the theory which would have them come 

 from Norway is exploded, especially in the absence of all evi- 

 dence of their existence there." § Now, we know that the flight 

 of locusts is generally very limited, and rather by leaping, at the 

 same time expanding their wings to support them ; but when im- 

 pelled by instinct, they can fly to a very great distance ; and who 

 would think that the little quail, avoiding to rise on the wing by every 

 art, had crossed the channel before it could arrive at our shores ? 

 It has long been my opinion that the appearance of rare insects 

 in this country is owing to their being brought over, guided by 



* Vide Mr. Marshall's paper in the Philosophical Trans, for 1 783, vol. 

 Ixxiii., and an abstract from his " Rural Economy of Norfolk," with a very 

 excellent preface by T. S. N. Published by J. Fletcher, Norwich, 1836. 



t Vide Journ. of Royal Agric. Soc, vol. ii. p. 201. 



% Journ. of Yorksh. Agric. Soc, p. 50. 



§ Athalia spinarum is found abundantly in France and Germany: it is 

 common in the southern portions of Sweden ; is an inhabitant of Holstein ; 

 and is met with everywhere in Lapland. 



