BY PLANTS AND VEGETABLES 465 



appearance an animal is compared with the ordinary natives 

 of a country, the more likely is its appearance in a native 

 fauna to be detected. Hence it comes about that the majority 

 of the stowaways recognized as imported with garden plants, 

 hail from distant and usually tropical lands, although the 

 factor must not be ignored that on account of their very 

 strangeness exotic plants are specially sought after by 

 collectors, and are imported, with their animal associates, 

 in large quantities. This tropical aspect adds a special 

 interest to the transportees of flowering plants, but the 

 peculiar adaptations imposed by the natural habitat of such 

 a fauna have prevented it from obtaining any secure hold 

 at large in Britain. Where they have escaped from the 

 genial warmth and moisture of the greenhouse, the exotic 

 aliens have as a rule, made only a spasmodic appearance in 

 our fauna. Even Mediterranean species, such as the White- 

 keeled Snail {Helix limbatd) and JBulimus decolletus, the 

 former of which was common in hedges around London in 

 1837, while the latter bred in great numbers in Devon for 

 many successive years about 1826, have generally a short 

 life and not always a merry one. Odd specimens of many 

 other Molluscs, introduced with plants, have appeared in 

 Britain only to disappear again. 



Nevertheless, native faunas have been occasionally en- 

 riched by plant transportees. There is strong presumption 

 that a number of our familiar types of Earthworms (Liimbri- 

 cidae), which are common to this country and to North 

 America, accompanied the early settlers and their chosen 

 plants from the Old \Vorld to the New. Or take that plague 

 of bulbs, the Narcissus Fly (Merodon equestris] whose grubs 

 feed upon the juicy scales of the bulbs, not only of Narcissus, 

 but of half a dozen genera besides. A native of southern 

 Europe, the Narcissus Fly has spread to northern Europe, 

 causing serious damage every year amongst the bulbs of 

 Dutch growers, and it was first noticed in Britain in 1869. 

 The later wanderings of infested bulbs have established the 

 pest in Canada, in the United States of America and in New 

 Zealand. It is probable also that the curious "Snail-slug," 

 Testacella maugei, which carries its shell on its tail instead of 

 on its back, was introduced with the soil in which it lived. 

 Its native abodes are in south-western Europe, Madeira, 



R. 3 



