Henry Bates: Discovery on the Amazon

In 1848, the bank of the Amazon River was not where you'd expect to find an apprentice stocking-maker from Leicester in England.

However, self-taught British naturalist and entomologist Henry Walter Bates (1825-1892) spent 11 years collecting butterflies in the Amazon in Brazil.

Bates and fellow aspiring naturalist Alfred Russel Wallace, arrived in Brazil in 1848 and travelled parts of the Pará and Tocantins rivers together.

The two friends went their separate ways that same year, with Wallace ascending the Rio Negro (towards Colombia) and Bates travelling deeper into the Amazon.

Bates collected these bright male and brown female butterflies (Nessaea obrinus) in the Amazon, in the Pará and Ega (now called Tefé) regions.

This description from a paper Bates wrote in 1864 paints a clear picture of the abundance of butterflies he encountered:

'In some places, during the fine season (August to October), they assemble by hundreds, sometimes thirty or forty species together, of the most varied shapes and colours, to sport about in muddy places exposed to the morning sun. Callicore and Asterope, with liveries of velvet crimson and black, or sapphire and orange; Eunica, with purple hues glancing in the sunlight as they fly; swallow-tailed Marpesia of many species; silky-green Dynamine; blue, white and black Baeotus, tailed like the Charaxes jasius of Europe, and many other kinds less conspicuous in colour and form, are all seen together, either settled on the ground or swiftly flying to and fro above it.'

Bates was a prodigious collector. It is estimated that he collected more than 14,000 different insect species, 8,000 of them previously unknown to Western science.

He was so prolific that the curators at the British Museum, who also took care of natural history specimens at the time, didn't believe it was possible that he had found so many.

Without the assistance of local guides, Bates would never have been able to navigate the remote areas of the vast Amazon rainforest and make the discoveries that he did.

Henry Walter Bates is best known for contributing to the theory of evolution through his study of mimicry.

Years of examining butterflies in the rainforests of Brazil allowed him to notice the way that otherwise vulnerable butterflies were in fact protected from predators. They copied the physical appearance of unpalatable or toxic species that predators had learned to avoid.

This is called mimicry.

In 1862 Bates published a scientific paper describing his ideas about mimicry. He believed harmless edible species occasionally produced forms with similar colour patterns to unpalatable toxic species. He believed these forms would be less likely to be attacked by predators, and would therefore pass on the same colouration to their offspring.

Bates's chain of 'transitional' Heliconius butterflies, collected during his trips to the Amazon, illustrate how biological populations can evolve to become distinct species.



Mimicry was seen as one of the strongest demonstrations of evolution by natural selection, in this case brought about through the actions of butterfly predators such as birds, dragonflies or lizards.

Without Bates's theory of mimicry it would have been difficult for Charles Darwin to persuade his readers that the idea of evolution was valid or that it operated by natural selection.