Female H. gammarus reach sexual maturity when they have grown to a carapace length of 80 – 85 millimetres ( 3 @.@ 1 – 3 @.@ 3 in ) , whereas males mature at a slightly smaller size . Mating typically occurs in summer between a recently moulted female , whose shell is therefore soft , and a hard @-@ shelled male . The female carries the eggs for up to 12 months , depending on the temperature , attached to her pleopods . Females carrying eggs are said to be " berried " and can be found throughout the year .