How do you build a home for an Adder?

The Mendip Hills AONB Service has built 15 ‘hibernacula’ across the area to help link populations of adders, a threatened species. Hibernacula are sites that adders can spend the winter in. 

Adder populations on the Mendip Hills are good but it’s important to help them spread out. Moving to new areas and mixing populations is important for keeping the gene pool healthy but it also means that if a site they’ve been using for some time is badly affected in some way the overall population can carry on. 

A hibernacula is an organised pile of stone; the ground surface is skimmed, large stones are placed at the bottom to create voids for the reptiles, then logs and smaller stone are piled on top up to a height of at least a metre. It should be south facing to absorb the sun’s rays and next to long grass, bracken or woodland edge for the adders to bask in and away from busy visitor areas. The AONB Service has produced a How to build a Hibernaculum Guide that you can download for free HERE.

The aim is to build hibernacula that maintain constant temperature and humidity at their core to protect the adders through the winter. To understand the best building technique the AONB Service has built five each of three different shapes; long barrow, round barrow and horseshoe. Each one has a monitoring tube built in so that the temperature and humidity can be monitored every month. Volunteer Rangers are being trained to survey the sites next spring and into the future to see what happens. 

Nathan Orr, Nature Recovery Ranger for the AONB Service said, ‘We know hibernacula are really important but this is the first time that three different types have been built and monitored, we’re excited to see the results. Protecting population strongholds like we have on Mendip is important but to help nature recover we have to focus on corridors and stepping stone so that they can spread out. Although we’ve built these with adders in mind we know they’re going to help lots of other reptiles, amphibians and invertebrates. Our thanks go to Natural England for the grant, all the landowners who let us build them and all the volunteers who helped.’

Adders are one of eight Champion Species for the area, chosen as figureheads for people to help as they represent good habitats. To find out more about the Champion Species and Nature Recovery Plan visit Nature Recovery Plan – Mendip Hills AONB