August 2010  - Grass Snakes

I have been privileged last month to have seen two grass snakes, one crossing Stocks Hill, and one sunbathing beside a path at the University of East Anglia (UEA). The grass snake, or water snake, is typically olive green or grey in colour, with a characteristic yellow/black collar behind the head. It loves water especially if surrounded by tall grass or reeds and with patience can be seen swimming in our rivers and lakes in the heat of summer. It can remain submerged for up to an hour. It has a ‘sit and wait’ policy when it hunts, and prey that comes within striking distance is caught and held in its backwards facing teeth before being swallowed whole. Its prey include frogs, toads, newts and fish and the odd water vole or water fowl chick. A snake can survive a whole year on as little as six or seven frogs. Female snakes are larger than males, and may reach 5 foot in length. The snakes I have seen around here over the years are all less than 4 foot in length. Old age for a grass snake is 25 years. Grass snakes are shy and will quickly disappear if they sense the vibrations of someone approaching. Unlike the adder, grass snakes are not venomous, and pose no risk to humans. If threatened they may emit a nasty garlic smelling liquid from their anal vent or feign death, as a deterrent to predators including herons and other birds of prey, foxes, and cats. Grass snakes hibernate from October to March/April, only emerging when the sun is warm enough to give them sufficient energy for their survival. Male snakes emerge from hibernation 2 weeks before the females, mating with them as soon as they emerge. The grass snake is the only native British snake to lay eggs. 10 to 40 leathery skinned eggs are laid in manure or compost heaps, or piles of rotting leaves or reeds. After about 10 to 12 weeks, depending on temperatures, the baby snakes hatch. Only the size of a pencil they are vulnerable and very few make it to adult life.

The casual observer may misidentify a grass snake as an adder, although the two species are very different. Adders typically have a dark zigzag pattern the whole length of their spine, with an inverted V shape on their neck. They do not have the yellow/black collar of the grass snake They also do not grow as large. I was upset a couple of years ago when found a dead grass snake on a path at the UEA. It had been beaten to death by a tree branch. It may have been killed by someone who hated all snakes, or it may have been killed by someone mistaking it for an adder. I have heard many reports of people seeing adders around here, but although I have seen many adders elsewhere, I have yet to see one locally.

lingibson@bawburghvillage.co.uk

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