An evaluation of techniques used in estimating snail populations.

No uniform method, applicable to all situations, can be developed for the quantitative study of bilharziasis vector snail populations. The selection of survey technique and sampling device depends on the objectives of the study, the circumstances in which the work is carried out, the nature of the habitat and the resources available.The various techniques used in obtaining snail-population estimates are divided into two categories-direct methods and indirect methods. The former involve the collection of snails from a specified habitat or for a specified period of time, while the latter include techniques, such as snail marking and palm-leaf traps, in which the snails are not obtained through the efforts of a collector. Each method and device is described in detail, and its suitability under various conditions is discussed.