perceived association with ponds and water. Grass snakes, like most reptiles, are at the mercy of the thermal environment and need to overwinter in areas which are not subject to freezing. Thus, they typically spend the winter underground where the temperature is relatively stable. Reproduction As spring approaches, the males emerge first and spend much of the day basking in an effort to raise body temperature and thereby metabolism. This may be a tactic to maximise sperm production, as the males mate with the females as soon as they emerge up to two weeks later in April, or earlier if environmental temperatures are favourable. The leathery-skinned eggs are laid in batches of eight to 40 in June to July and hatch after about 10 weeks. To survive and hatch, the eggs require a temperature of at least , but preferably , with high humidity. Areas of rotting vegetation, such as compost heaps, are preferred locations. The young are about long when they hatch and are immediately independent. Migration After breeding in summer, snakes tend to hunt and may range widely during this time, moving up to several hundred metres in a day. Prey items tend to be large compared to the size of the snake, and this impairs the movement ability of the snake. Snakes that have recently eaten rarely move any significant distance and will stay in one location, basking to optimize their body temperature until the prey item has been digested. Individual snakes may only need two or three significant prey items throughout an entire season. Ecdysis (moulting) Ecdysis occurs at least once during the active season. As the outer skin wears and the snake grows, the new skin forms underneath the old, including the eye scales which may turn a milky blue/white colour at this time—referred to as being 'in blue'. The blue-white colour comes from an oily secretion between the old and new skins; the snake's coloration will also look dull, as though the animal is dusty. This process affects the eyesight of the snakes and they do not move or hunt during this time; they are also, in common with most other snakes, more aggressive. The outer skin is eventually sloughed in one piece (inside-out) and normal movement activity is resumed. Defence In defence they can produce a garlic-smelling fluid from the anal glands, and feign death (thanatosis) by becoming completely limp when they may