28 Nov 2016

Stop Copying Me! Butterfly mimicry

Ardd Fotaneg · Botanic Garden

At Plas Pilipala we have many different butterflies with dozens of different colours and patterns, but you may not have noticed how similar some of them look. These masters of mimicry are the Heliconiini.

The Heliconiini are a tribe of butterflies from 12 different genera. All of them are characterised by having long wings, and most are red and black or orange and black in some form. Some of the Heliconiini we have at Plas Pilipala include Heliconius melpomene, the Postman; Heliconius hecale, the Tiger longwing; and Dryas iulia, the Julia longwing.

Heliconiini are found all over the world, but the ones we have at Plas Pilipala are native to Central and South America. Most Heliconiini are toxic because their larvae eat Passion flower (Passiflora) leaves, which are poisonous. When the caterpillars eat the leaves, the caterpillars take on the poison, making both the caterpillars and adults of these species unpalatable to birds. Many Heliconiini are brightly coloured to warn predators that they are dangerous.

On his travels to Brazil, naturalist Henry Walter Bates observed that some Heliconiini were always found with other near-identical unrelated species, which flew in the same habitats and had the same predators. Bates then discovered that the species from the Heliconiini tribe were poisonous to predators, whereas the other species were not, and these species were merely copying the poisonous species. He noticed that neither the poisonous species or the mimicking species were commonly predated by birds. This is because predators learn not to eat the toxic species and recognise their colouration, and when the mimic is mistaken for the toxic species they are protected from predation. This phenomenon became known as Batesian mimicry. This discovery is considered to be one of the founding discoveries of evolutionary ecology.

Heliconiini species not only exhibit Batesian mimicry, but also a lesser-known version of mimicry called Müllerian mimicry. Described by Fritz Müller, Müllerian mimicry occurs when two harmful species which share a common predator mimic each other in order to emphasise the message to predators that they are dangerous. This can be seen in many Heliconius species such as H. melpomene which mimics Heliconius erato. The colour pattern of H. erato is different every 100-200 miles in their native habitat, but H. melpomene also mimics this, making the markings of H. melpomene similarly distinct in different geographical regions and also making the two species very difficult to tell apart. Heliconius butterflies are considered a classic example of this phenomenon.

While mimicry is very common in Heliconius species, they aren’t the only ones with a trick up their sleeve. Other species such as Tithorea harmonia, named the Harmonia Tiger for its orange and black stripes, is another toxic butterfly which is also commonly mimicked by other species. These distinct markings are common across many butterflies and they have become known as the ‘tiger complex’.

The discovery of both Batesian and Müllerian mimicry were used as early evidence for evolution by natural selection, therefore having a huge influence on how we see our world today.

While mimicry is very beneficial for the butterflies, it can make it very hard for our butterfly rangers to tell some of the species apart. Plas Pilipala is open from 10:00am until 4:30pm every day!