12 WOODLICE 



size of populations before parasites can increase sufficiently to be- 

 come of ecological importance. 



Reproduction and life cycle 



Like other Crustacea, woodlice carry their eggs in a thoracic 

 brood pouch or marsupium and a whole family of newly hatched 

 young may be found huddled up on the underside of the mother. 

 The number of eggs varies from seven per brood in Trichoniscus to 

 100-200 or more in Armadillidiutn. 



The newly hatched larvae have a distinct head and eyes, seg- 

 mented body and short, stumpy limbs. They are incapable of 

 movement for the first three days as their appendages are tightly 

 doubled against the body. At this stage they are kept very moist, 

 but as their size increases the fluid in the brood pouch decreases. 

 The young emerge over a period of two or three days and the first 

 moult occurs within 24 hours of liberation. The period between the 

 first and second moult is the most critical in their lives, because if the 

 soil is dry at this time they die, while if it is too moist they are usu- 

 ally killed by fungi. Later they are more resistant and their life may 

 be quite a long one, for they seldom breed until they are two years old. 



The life cycle oiLigia oceanica lasts for three years according to 

 Nicholls (1931). At least five broods of young are produced, and 

 the average number of young per brood is 80. The time taken for 

 the development of the young varies from 40 days in summer to 90 

 in winter, and although the greatest number of animals with brood 

 pouches is found in spring, breeding occurs throughout the year. 

 The greatest interval between moults occurs in full-grown males 

 in winter, the shortest in young specimens during the summer. 

 The growth rate was observed in a young specimen to average 1-3 

 mm increase in length and 0-5 mm in width per month. Copula- 

 tion occurs after the appearance of the mature brood plates in the 

 female. The ova are spawned about two days after the completion 

 of the moult and, if unfertilised, remain viable for at least three 

 days subsequent to their appearance in the brood pouch. Heeley 

 (1941) found that the respective durations of the successive stages 

 in the breeding processes, especially the embryonic and larval 

 periods, whilst varying in different species are more or less con- 

 stant for each particular species. These periods range from an 



