Simple experiments and field studies with earthworms

Abstract

Earthworms can be kept in culture in almost any large vessel, provided that it is non-porous (otherwise it will be difficult to keep the soil sufficiently moist) and large enough, its actual size depending on the numbers of worms in the culture. Some species of earthworms produce their normal number of cocoons, only if given more space than they require to live and remain healthy. ‘Stocks’ of earthworms can be kept in large glazed earthenware pots, about 12 cm diameter and 30 cm deep, with the top covered with muslin, although for experimental purposes, smaller vessels are usually preferable, so that the amount of soil required is not excessive. Glass jars, such as ‘Kilner’ jars, having wide mouths are very suitable for earthworm experiments. Evans and Guild (1948) successfully maintained cultures for the study of cocoon production, with three earthworms per 5-pint (2.85-litre) capacity jar (Lumbricus terrestris), five per 3-pint (1.71-litre) capacity jar (Allolobophora longa) and five per 1-pint (450-ml) jar for smaller species such as Allolobophora caliginosa, Allolobophora chlorotica and Allolobophora rosea. Normally cultures should be kept in a cool building or cellar at a temperature between 10°C and 15°C or buried in soil. The ideal culture medium for most of the common pasture and garden species is a friable loam with 25–30% moisture content (such that it will remain in a ball when lightly squeezed in the hand). Food can be any partly-decomposed plant material, such as moist horse or bullock droppings (if these are dried before use, cocoons introduced with the food material will not be viable), partly rotted straw or tree leaves (not beech leaves). Cocoons can be obtained from field soil by washing it through a 1 or 2 mm sieve with a jet of water, so that they can then be picked off the sieve, or floated off by immersing the sieve in a solution of magnesium sulphate (specific gravity 1.2). Cocoons can also be kept in containers of soil, but if the time of hatching is to be studied, and to ensure the newly-emerged worms are not lost, they are better kept on moist filter paper in petri or other glass dishes, or under water in specimen tubes. Cocoons can be identified from their size (Table 25) and their shape (Fig. 61).