The hard shell…

In this episode of Life in Cold Blood, Sir David Attenborough looks at the evolution of hard shelled eggs and how this adaptation helped the lizards conquer the planet. In temperate regions like the UK however, it’s difficult for some lizards to fit feeding, courtship, breeding and preparing egg-laying sites, into just two seasons: spring and summer. So two of the UK's lizards use another strategy, that of carrying eggs internally and then giving birth to live young. 

Throughout the summer, young of both Common Lizard (July) and Slow Worm (mid-August to mid-September) are born within an egg membrane (rather than a hard shell) and once free, are fully-formed and then able to feed. The method of producing live young in this manner is called viviparity, hence the Common Lizard’s other name: the Viviparous Lizard.

A good time to see Common Lizards is when the young have recently emerged. Visit lizards sites quietly in August and you might see large numbers of juvenile lizards within a few metres. They have probably only recently hatched, and have not yet dispersed into surrounding areas. Make a note of the site, and make sure you pass on a record of your encounter – www.arguk.org. You can learn more about where your nearest lizard colonies are by contacting your local Amphibian and Reptile Group (www.arguk.org) or Wildlife Trust (www.wildlifetrusts.org).

Incredibly, some populations of Common Lizard on the European mainland (most notably in the Pyrenees and northern Spain) also lay hard-shelled eggs externally in clutches, allowing development to occur at the mercy of environmental temperatures.

In the Uk, only the Sand Lizard lays hard-shelled eggs, laying four to 12 leathery eggs in specially made burrows, which it then leaves. Young hatch seven to 12 weeks later, depending on temperatures. In some warmer years, Sand Lizards are able to ‘double-clutch’ laying eggs in both late May and early July.

Heads or tails

Perhaps the most remarkable feature, which all of the Uk's lizards possess, is the ability to shed their tail. If a lizard is being attacked by a predator or feels threatened, it is able to contract muscles in its tail that essentially fractures it off. This bizarre talent is the lizard’s last ditch attempt to move the predator’s attention from the body (where all the crucial bits are) to the tail. Often this strategy works: the lizard quietly skulks away while the predator is left fighting with a (still thrashing!) tail.

Rockery and roll

Both Common Lizards and Slow Worms are known to frequent gardens, driven by a hunger for woodlice, ants, snails and slugs.

You can make your garden that bit more lizard-friendly by creating a reptile rockery, which offers lizards places to hide, places to bask, places to hunt and places to hibernate. For more information contact Froglife’s Wildlife Information Service.

Next episode: Snakes in the City

Episode 1: Cold Blooded in a Cold Climate
Episode 2: Battlefield Pond
Episode 3: Dragon's Den UK
Episode 4: Snakes in the City
Episode 5: Visitors to UK Shores
Epilogue: Froglife in Cold Blood

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BBC Life in Cold Blood
ARG UK
British Herpetological Society
Herpetological Conservation Trust