Aposematic Variation
Why Blend in when you were born to stand out? This could be the motto for species which have evolved to be aposematic. Aposematic variation is a term used to describe species which advertise their defence mechanisms to potential predators. This is usually in the form of bold colours and striking patterns making the species highly visible. It could also be a certain noise they make, protruding spikes, odour, bad taste of the organism or even a chemical deterrent. It is basically a warning sign that says, ‘stay away’. These signs, smells and characteristics of the prey make the predator weary, potentially resulting in the predator avoiding the prey altogether.
Some of Irelands butterfly larvae are aposematic. For example, the Marsh Fritillary (Euphydryas aurinia) larvae do not camouflage themselves, instead they feed openly in large groups. They are covered in black bristles which can cause injury to potential predators. If a bird does try and grab one of these the larvae will place its mouth against the bird’s beak and vomit a vile smelling and tasting deterrent. The bird will then release the larvae. At this stage most are still unharmed and will drop to the ground into a ball with its spikes protruding in case it is attacked again.
The beloved Seven Spotted Ladybird (Coccinella septempunctata), a colourful member of the beetle family is also aposematic. Because of its bold colours and patterns, it is easily recognisable to us. But why has this little beetle evolved to stand out when surely for survival it would be better to not be seen by predators? Research in fact suggests the brighter the ladybird the less likely it is to be eaten. Interestingly the brighter the ladybird the more toxic it is to predators too.
The Cinnabar Moth (Tyria jacobaeae) and Six-Spot Burnet Moth (Zygaena filipendulae) are very noticeable because of their bright red and black colours. In the caterpillar stage the Cinnabar Moth feed on Ragwort. They then store toxic chemicals from the plant, making them distasteful to predators. The Six-Spot Burnet Moth are naturally toxic and when attacked they will release hydrogen cyanide. Both these moths can be found in overlapping areas and because of their similarities it reinforces their chance of survival.
Some species even mimic others to protect themselves. This is probably most obvious in the hoverfly. It has similar markings to a wasp and even though the hoverfly does not sting or bite, predators often associate black and yellow marking with wasps that do sting, and this can be enough to keep them safe from predators.
Studies have shown that Aposematic Variation often proves more effective as a defence mechanism than camouflage or hiding from potential predators. The more widespread a species the better this technique works. This is because more predators will remember a previous bad encounter and will learn to avoid such prey.
The next time you are outside keep an eye out for organisms which seem to stand out against their natural habitat. They may be aposematic!
Written by Mary Moroney
References
https://butterflyconservation.ie/wp/2019/04/12/
https://www.irishexaminer.com/opinion/columnists/arid-20338199.html
https://doi.org/10.1371/journal.pone.0091777.
Caretaker of the Cork Nature Network website
