Lizards and random musings on evolution and superstition.
One of the (many) reasons Thursley is my favourite place to walk is how many lizards we see from spring to autumn. It’s one of the few remaining sites that hosts the endangered sand lizard, but since they are both very rare and very shy, I haven’t and don’t expect to see one.
What we do see lots of, however, is the common lizard, Zootoca vivipara. One of the reasons that I’m endlessly fascinated by them is that their colouring is incredibly variable. They range from pale brown with very definite markings (or, very rarely, pale with no markings), to blue-black all over. The males tend to be spotty while the females tend to stripiness. There is lots of information about them here, but here are a few interesting facts.
The common lizard is the only reptile to be found in Ireland. Maybe they foxed St. Patrick with their myriad colours. 😉 They are, in fact, found in all of Europe, and have a more northerly range than any other reptile. What is really interesting, though, is how they have adapted to those conditions. In warm southern climes, Z. vivipara lays eggs like most other lizards. In the cold north, however, where it’s too cold for their eggs to develop, they have adapted in spectacular manner. Instead of laying eggs with a tough outer membrane, they incubate the eggs internally. The young develop in the inner egg sac and don’t develop the outer ‘shell’. The baby lizards break out of their egg sac at or soon after birth. Hence the name vivipara, meaning ‘live birth’. Yet they still develop in an egg. Or do they?
Discovering this made me think of how narrow the divide is between mammals and egg-laying species. Us humans, as do other mammals, develop in the amniotic sac – the inner membrane of the egg, pretty much. We break out of our
egg amniotic sac before, during or after the moment of birth – known as the breaking of the waters. I have witnessed the birth of a baby born ‘in the caul’ – within the egg unruptured amniotic sac – and it used to be judged as very lucky. Sailors and fishermen would pay highly for a piece of the ‘caul’ of the child born within unruptured membranes. Because the baby was born into the world still swimming and breathing in fluid, the sailors thought that this would protect the child (and anyone who possessed the lucky charm of a bit of the membranes) from ever drowning.
Anywaaaaaaay..! Back to lizards. 😉 The young were born in late August/early September. Suddenly, on the boardwalk, appeared dozens of tiny, inch long lizards, scurrying away only when you get right up to them. Z. vivipara thrive at Thursley due to the areas of boardwalk. It’s the ideal habitat for them; warm wooden areas that heat up in the sun for them to bask on, and secluded and protected areas underneath for them to shelter and hibernate. As ‘cold blooded’ creatures – meaning that they can’t regulate their own temperature in the way that we mammals can – they need warmth to get their metabolism up to speed in the morning, so to speak. Reptiles need to move to a warm area when they are cold, and move to a cool area when they are too hot. They don’t have any of the homeostatic balancing mechanisms that mammals have, like sweating, panting, shivering etc.
Well that’s all for now – time for my dinner. I hope you enjoyed a crash course in lizards and some pictures of lizards at Thursley.