ABSTRACT
III In¯uence of Environmental Factors on Survival and Growth of Earthworms ................................................................................................. 35 A Temperature ..............................................................................................36 B Moisture Content ......................................................................................36 C pH .............................................................................................................36 D Aeration .................................................................................................... 37 E Ammonia and Salts ................................................................................... 37
IV Predators, Parasites, and Pathogens of Earthworms ....................................... 38 Acknowledgment ..................................................................................................... 38 References ................................................................................................................ 38
I INTRODUCTION
Earthworms are macroscopic clitellate oligochaete annelids that live in soil. They are segmented worms, bilaterally symmetrical, with an external gland (clitellum) for producing the egg case (cocoon), a sensory lobe in front of the mouth (prostomium), and an anus at the end of the animal body, with a small number of bristles (setae) on each segment. They are hermaphrodite animals, and reproduction normally occurs through copulation and cross-fertilization, following which each of the mated individuals produces cocoons containing 1-20 fertilized ova. The resistant cocoons, which are tiny and roughly lemon-shaped, with shape differing between species, are usually deposited near the soil surface, except in dry weather when they are laid at deeper layers. Cocoons hatch after an incubation period that varies according to the earthworm species and environmental conditions. Hatchling earthworms, unpigmented and only a few millimeters in length on emerging from the cocoons, gain their adult pigmentation within a few days. Assuming favorable conditions, they reach sexual maturity within several weeks after emergence. Mature individuals of most vermicomposting species can be distinguished easily by the presence of the clitellum, the pale-or dark-colored swollen band located behind the genital pores. The clitellum secretes the ¤brous cocoon, and the clitellar gland cells produce a nutritive albuminous ¯uid that ¤lls the cocoon. Earthworms display indeterminate growth and can continue to grow in size after completing their sexual development although they do not add segments.
