134 Zoology of Colorado 



SLUGS 



Slugs are distinguished from snails by the apparent absence 

 of a shell. In some genera it is totally absent; but in the Lima- 

 cidae, to which our Colorado slugs belong, it is represented by a 

 flat plate concealed beneath the skin. In other countries there 

 are animals in which the shell is clearly visible on the outside, 

 but still so small that we class them with the slugs rather than 

 with the snails. Such is the carnivorous slug of Europe, Testa- 

 cella, which feeds on earthworms. The Pacific coast region of 

 the United States is rich in slugs, some of them very large, but 

 in Colorado we have only one native species. This is a small dark 

 or pale brown form common in the mountains, under stones in 

 damp places. Ingersoll, in the Report of the Hay den Survey for 

 1874, described two supposed new species, Limax tnontanus from 

 Hot Sulphur Springs, and Limax castaneus from the Blue River 

 Valley. The first of these names could not be used in any case, 

 as there is an earlier Limax montanus Leydig, 1871. This is 

 however a matter of small moment, for it appears certain that 

 both Ingersoll's slugs are referable to Agriolimax campestris 

 Binney, described in 1841 , and known to be very widely distributed 

 in North America. This A. campestris, in turn, is with difficulty 

 separated from the European and Asiatic A. Iaevis, so that it seems 

 to deserve only subspecific rank. Very dark, nearly black, ex- 

 amples of the Colorado slug have been described as a variety 

 tristis; they seem to be very frequent at high altitudes. 



The slugs of this group present a curious biological problem. 

 They are found all around the world, and in tropical as well as in 

 temperate countries. They exist in Australia and on the remote 

 islands of the Pacific, as well as in Jamaica and Brazil. Various 

 authors have described them as distinct species, but the differ- 

 ences are slight, and in many cases it is very doubtful whether 

 they are really indigenous in the places where they have been 

 found. The student of geographical distribution recoils from the 

 proposition that a slug found in Labrador and the Commander 

 Islands can belong to the same species as one from Brazil and 

 Madagascar. The matter deserves renewed study, with more 

 abundant materials than any single author has yet possessed; 

 but certainly, whether there is one species or a series of them, the 



