December, 1903.1 289 



VANESSA CARDUI AND OTHER INSECTS AT THE KENTISH 

 KNOCK LIGHTSHIP. 



BY WM. EAGLE CLAEKE, F.R.S.E , F.L.S. 



With the permission of the Elder Brethren of the Trinity House 

 I spent thirty-one days (September 17th to October 18th) on the 

 Kentish Knock Lightship, for the purpose of making observations on 

 the migrations of birds, a subject in which I am specially interested. 

 During the fine weather that characterized the latter part of Septem- 

 ber a considerable number of insects appeared on board the ship, a 

 few of which I captured. Among them were several specimens of 

 Vanessa cardui, which, strange to say, were secured as they fluttered 

 with others of their kind against the lantern, from 8.45 p.m. to 

 midnight on September 22nd, and I saw a number flying round the 

 vessel on the following day. These remarkable facts may perhaps 

 explain the recent abundance of this species on the east coast of 

 England and elsewhere in Britain during the past autumn, since they 

 decidedly point, in my opinion, to immigration from the Continent ; 

 and this view is further supported by the fact that the wind at the 

 time was south-easterly and light. 



The Kentish Knock Lightship is situated in the North Sea, 

 N.E. of the mouth of the Thames, 21 miles from the nearest points 

 of the land, which are Margate and the Naze (Essex), and lie re- 

 spectively S.W. by W. and N.W. from the vessel. The nearest 

 points to the Continent are the northern coast of France and the 

 Belgian coast, which are distant from 48 to 5G miles, and lie S.S.E. 

 and S.E. from the Lightship. 



On September 23rd, in addition to the butterflies, there came a 

 number of Plusia gamma and hundreds of small Trichopterous insects, 

 which my friend Mr. Kenneth J. Morton has determined as Limno- 

 philus griseus, L., and L. affinis, Curtis. The presence of these latter 

 is also strongly suggestive of migration from the Continent, for it 

 is scarcely possible that such delicate insects could have flown for at 

 least 21 miles against the gentle breezes which prevailed, as they must 

 have done if they came from the south-east coast of England. Two 

 specimens of the fly HelopJiilus trivittatus and one of Sphcerophoria 

 (named by ray colleague Mr. P. H. Grrimshaw) appeared at the same 

 time, and many other species, including a Tortrix, a Plume moth, and 

 a Hemipterous insect, which I have been unable to determine. On 

 the morning of September 28th I took fine fresh specimens of 

 Ennomos ahiiaria (male) and Apamea testacea at rest on the lee side 

 of the deck house. 



