Our research on the grass snake


Manure heaps and compost piles are important for the grass snake

The Swedish climate is relatively cool even in the summer and therefore challenging for snakes and other heat-loving reptiles. Egg-laying species may find it particularly difficult to find nesting-sites with temperatures that are warm enough for the eggs to hatch. However, grass snakes have solved this problem in an ingenious way. They simply lay their eggs inside manure heaps (farmers in many European countries traditionally store manure in large heaps to use as fertiliser) and compost piles, and thus take advantage of the heat that is generated by the rotting material. We are researching this unusual nesting behaviour and have made many exciting discoveries!

The grass snake: habitat, distribution and reproduction

1. How do changes in incubation temperatures affect the babies?
Snake eggs are sensitive to changes in the temperature. At low temperatures (around 20 degrees Celsius) eggs develop slowly and the hatchlings are small and slow. Inside manure heaps temperatures are around 27-30 degrees Celsius and at these temperatures the hatchlings are large and fast. We are interested in how these differences affect the snakes later in life.

2. How are Swedish reptiles adapted to the cold climate?
Most cold-climate reptiles give birth to live young. In Sweden only grass snakes and sand lizards lay eggs. Females of all other species (vipers, smooth snakes, slow worms, common lizards) retain their eggs inside the body where they are kept warm until they hatch. It is often said that these species give birth to live young. We study the significance of this adaptation.
3. In what ways can female snakes help their eggs?
Females snakes seek out warm environments to lay their eggs. This increases their chances of hatching. However, females can probably also help their eggs in other ways. For example, females often lay their eggs in clusters with the eggs of other females. We are investigating whether this changes the temperature and humidity in the nest in a positive way for the eggs.
Bild: Graf
Both the number of holdings with livestock and the number of grass snakes deposited in museum collections has decreased in Sweden in the last 80 years. Data for slow worms were included as a control group for the possibility that the trend in grass snakes was due to changed reporting rates rather than reflecting actual population trends. The figure was originally published in The Herpetological Journal 2012.
bild snok
The body color of grass snakes varies from black, brown, gray and even bluish or greenish.

Research helps us understand the grass snake

1. How are grass snakes affected when their nesting-sites disappear?

The number of farms with livestock holdings has decreased sharply in Sweden. Because of this there are fewer manure heaps (farmers traditionally stored manure in heaps to use for fertilising) where female grass snakes can lay their eggs. We are investigating whether this is a threat to the survival of grass snakes in Sweden and iwhat we can do to help them.

2. How can we help the grass snake?
Grass snakes need access to warm nesting-sites where their eggs can develop. Female also lay their eggs inside composts and maybe these micro-habitats can function as a substitute for the dwindling manure heaps. Because grass snakes are decreasing in numbers, it is important that their eggs are left undisturbed if you happen to find some in your compost.

We need grass snakes because

  • They are important in the food chain. Snakes are predators that keep other species in check. Grass snakes do that by eating toads, fish and rodents. Grass snakes also has many enemies because they are themselves important food for many other predators.
  • Crows and foxes are a two examples of animals that like to eat snakes. If grass snake disappear, it can disrupt the ecosystem.
  • Grass snake also have an aesthetic value, just like other species. The loss of species is loss of biodiversity.

This post is also available in: Swedish