September 2013

Many Naturalists spend lots of time watching species so as to understand how they fit in with Nature.  There is a lovely story of two 19th century naturalists, Fritz Müller and Henry Bates.  Both were fascinated by the fact that unrelated species often had similar shapes, colours and/or marking patterns.  They discovered that some species of animal have evolved to mimic others, and by doing so, enhanced their survival probabilities.  To understand this, it is necessary to understand warning signals.  Although many species of animal have camouflaged or cryptic bodies that hide them away from predators (e.g. green or brown frogs hiding from cats and snakes), some animals are brightly coloured (e.g. ladybirds).  It turns out that ladybirds are both toxic and distasteful when eaten, so that predators (usually birds) avoid them.  However, frogs are apparently good to eat, so need the ability to hide from predators.  So, if another species of beetle becomes red, but is also good to eat, predators will tend to avoid it because of its colour, and even though it is good to eat, it is more likely to survive and have offspring.  This is known as Batesian mimicry after Henry Bates.  It also works for flowers where plants that do not provide nectar mimic others that do, so that insects will pollinate them even if they do not provide a reward.

Fritz Müller went to South America and found that many species of butterfly, some closely related, and others not, all had similar shapes and markings, and all were toxic and distasteful.  So why were they all looking similar if they were all toxic or distasteful?  It turns out that even if an animal is bad to eat, it is less likely to be eaten if it looks like another animal that is bad to eat.  It is easier for a predator to learn one warning signal than lots of different signals. So appearances tend to converge over many generations.  So this is known as Müllerian mimicry.

There are many other types of mimicry in nature, such as the peacock butterfly, that has false eyes on its wings.  When its wings are closed it is cryptic and camouflaged.  However, if it moved, it may be spotted by a predator, if this happens, the butterfly suddenly opens its wings and the predator sees 2 huge eyes ‘looking’ at it and should jump back, giving the butterfly time to escape.