SOME SNAILS AND SLUGS OF QUARANTINE SIGNIFICANCE 
TO THE UNITED STATES 
By John B. Burch 1/ 
ECONOMIC IMPORTANCE 
The economic importance of snails and slugs to man may be considered 
from two different aspects - that of a ''positive'' or beneficial nature and 
that of a ''negative'' or harmful nature. Only the negative aspects will be 
dealt with in this publication. From this point of view the economic im- 
portance of snails and slugs comes under three general categories: (1) 
Destruction of crops and gardens; (2) medical importance, both to man 
and his domestic animals; and (3) indirect effects resulting from immi- 
grant mollusks affecting the balance of natural communities of plants and 
animals. 
Destruction of Crops and Gardens 
The land snails and slugs are of most concern as agricultural pests, while 
the fresh-water snails are of greater importance from the medical stand- 
point. Approximately 725 species of land snails and about 40 species of 
slugs are now recognized in the United States (exclusive of Alaska and 
Hawaii). Of these species 55 (44 snails and 11 slugs) are not native to the 
country, but they have been introduced either accidentally or purposely. 
The native species are solitary in habit and do very little damage. The in- 
troduced snails and slugs are the most undesirable, because they are gre- 
garious or colonial and may cause great damage by building up enormous 
populations over limited areas. They are of considerable economic im- 
portance through their depredations in greenhouses, gardens, and orchards. 
In many places they have caused as serious a damage to vegetables, orna- 
mentals, and other plants as certain insect pests. Snails and slugs through 
their presence on walks, around foundations, and in cellars are also an- 
noying to householders, Eradication of these pests is difficult and often 
costly. 
Among the more serious foreign garden pests already established in this 
country are the slugs Limax maximus, L, flavus, and Deroceras reticu- 
latum. Commercial interchange of plants, cuttings, and floricultural 
materials facilitates their dispersal. The snails Helix aperta and Otala 
lactea have become established in California and considerable expense, 
time, and energy have been devoted to combating them, Theba pisana, 
1/ Research Associate, Museum of Zoology, University of Michigan, 
collaborating with the Plant Quarantine Division, ARS, U. S. 
Department of Agriculture. 
