Classification of Soil Invertebrates According to Feeding Habits.

Phyto-
phagous.		Sapro-
phagous.		Carniv-
orous.		Hetero-
phagous.
Unmanured plot14481320
Manured plot1358 920

From the point of view of the fauna as a whole, the zoological classification of the soil invertebrates is only significant when the various groups are analysed according to the feeding habits of their members. All animals are directly or indirectly dependent upon plant life for their nutrition. For the present purpose they are divided into four categories, and the position of each class of animals in the scheme is based upon the habits of its chief representatives in the soil. Definite information on this subject, however, is not always forthcoming, and it is only possible to achieve approximate estimates. In the table above the percentages in number of individuals present in the two plots investigated at Rothamsted are given under each type of feeding habit.

It must be borne in mind that these estimates only apply to average conditions; the outbreak of a plant pest in any one year must naturally materially alter the proportions given. The phytophagous organisms are represented by a certain number of the Insecta together with the pulmonate Mollusca. Carnivorous forms which are mainly beneficial from the agricultural standpoint, include Insecta, together with the Chilopoda, many Acarina and the Areinida. Saprophagous forms constitute the dominant element of the soil fauna. More than 30 per cent. of the Insecta exhibit this habit, which is also the dominant one in the Oligochæta, Symphyla, and in many of the soil Nematodes. Heterophagous species include all those of somewhat plastic habits; for the most part they are saprophagous, but, on the other hand, a considerable proportion of the species attack growing plants or exhibit both habits. Under this category are included a certain number of the Insecta, the Diplopoda, Isopoda, and some Acarina.