Our research on the grass snake

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Introduction to the grass snake project

We are working on different projects, where we carry out experiments in nature and in the laboratory to learn more about the grass snake. We use everything from advanced climate chambers and digital measuring devices to ordinary copying machines and inflatable swimming pools. See our resource page for more information.

Reproduction, habitat and distribution

Female nesting behaviour

Most female snakes abandon their eggs after laying. Snake therefore have a reputation of being bad mothers. However, female snakes are very careful when choosing where to lay their eggs, because the nesting-environment has a major influence on both the development of the eggs and the hatchlings. So they are better mothers than it may appear. Females often also lay their eggs together with the eggs from other females. We are trying to understand why they do that.

bild: Snake Researcher at work on a dunghill.

Snake researcher at work. Photo: Nicolina Bjureus

Bild inkuberade snokägg i klimatskåp

Snake eggs incubating in a climate chamber. Each cup contains one egg.

Our projects are constantly evolving. Please check back to stay up to date on our research!

Nesting sites and their importance for the eggs and hatchlings

Temperatures within the nest affect how the eggs develop and how the babies look and behave after hatching. For example, temperature affects their size and how fast they can swim.

We want to understand how different nesting environments affect the snakes. What the consequences are of temperature variation. To do this we incubate snake eggs in the laboratory at different temperatures. Then we measure how it affects the babies, their size and other traits. Even relatively small differences in traits may have a major impact on how the babies will survive in the wild.

One objective of our research is to understand whether there is a link between incubation temperatures and the ability of the hatchling to survive. This is important if we want to understand how changes in climate and the environment will affect the snakes, and also what we can do to help them.

Every year we release baby snakes that we hatched at different temperatures. We can recognise individuals by looking at the colour patterns on their belly. Each grass snake has a black and white pattern that is unique, like a fingerprint. In the future we hope to recapture some of the hatchlings that we released when they have become adults. If we do that, we can understand if there is a relationship between the temperature they experience inside the egg and how they survive after hatching.


Our research shows that warm compost and manure heaps are good environments for hatching snake eggs. This has probably helped the grass snake to colonise cold-climate areas like Sweden. In support of this, archaeologists have found 7000 year old fossilised grass snake eggs in manure heaps in northern Europe.

According to old books and other writings, grass snakes used to be common even in the far north areas of Sweden. Today it seems that the have disappeared from the north of the country. One hypothesis that might explain why they no longer exist in northern Sweden is that there are fewer manure heaps and compost today where the females can lay their eggs.

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Threats and Conservation

Unfortunately, agriculture is changing and nowadays there are fewer farms with manure heaps. In addition, there is law that large manure heaps must be enclosed by a concrete wall. This is unfortunate for grass snakes, because it means that they have fewer places to lay their eggs.

if snakes are restricted to nest in less then optimal habitats, the eggs may not hatch and then there will be no new babies. We are therefore investigating what we can do to help them. For example, if we can build special nesting sites where they can lay their eggs so new baby snakes can hatch.


  • Löwenborg K & Hagman M. 2016. Scale asymmetries and lateral rib duplication in snakes: correlates and effects on locomotor performance. Biological Journal of the Linnean Society (in press)
  • Hagman M, Löwenborg K. & Shine R. 2015. Determinants of anti-predator tactics in hatchling grass snakes (Natrix natrix). Behavioural Processes 113: 60-65.
  • Hagman M, Kärvemo S. Elmberg J. & Löwenborg K. 2013. Life at the edge: the nesting ecology of the world’s most northerly oviparous snake and its implications for conservation. In: W.I. Lutterschmidt (ed.). Reptiles in Research: Investigations of Ecology, Physiology and Behavior from Desert to Sea. Nova Science Publishers, Inc. New York. ISBN: 978-1-62808-599-0.
  • Elmberg J, Hagman M, Löwenborg K. & Kärvemo S. 2013. Snokens barnkammare försvinner. Fauna & Flora (1)108: 10-16.
  • Löwenborg K, Gotthard K, & Hagman M. 2012. How a thermal dichotomy in nesting environments influences offspring of the world’s most northerly oviparous snake, Natrix natrix (Colubridae). Biological Journal of the Linnean Society 107: 833-844.
  • Löwenborg K, Kärvemo S, Tiwe A. & Hagman M. 2012. Agricultural by-products provide critical habitat components for cold-climate populations of an oviparous snake (Natrix natrix). Biodiversity and Conservation 21: 2477-2488.
  • Hagman M, Elmberg J, Kärvemo S. & Löwenborg K. 2012. Grass snakes (Natrix natrix) in Sweden decline together with their anthropogenic nesting-environments. The Herpetological Journal 22: 199-202.
  • Löwenborg K, Shine R. & Hagman M. 2011. Fitness disadvantages to disrupted embryogenesis impose selection against suboptimal nest-site choice by female grass snakes, Natrix natrix (Colubridae). Journal of Evolutionary Biology 24: 177-183.
  • Löwenborg K, Shine R, Kärvemo S. & Hagman M. 2010. Grass snakes exploit anthropogenic heat sources to overcome distributional limits imposed by oviparity. Functional Ecology 24: 1095-1102.
  • Löwenborg K, Kärvemo S. & Hagman M. 2009. Snokens vanor kartläggs. Fauna & Flora. (2)104: 42-45.

This post is also available in: Swedish