Carnivorous plants and Charles Darwin, lecture report


Norbert Peeters, 11 August 2017

On 11 August 2017, before we went to the carnivorous plants exhibition in the botanical garden, we went to a lecture in Leiden University about carnivorous plants and Charles Darwin. The lecture was by Norbert Peeters, on the left of this photo. The title of the lecture was Darwin’s little shop of horrors.

All photos on this blog post, mainly of slides shown during the lecture, are cell phone photos.

Today, Darwin’s best known book is On the Origin of Species. However, Peeters said, during Darwin’s life his best sold book was his 1875 Insectivorous plants.

Before Darwin, people either thought carnivorous plants did not exist; or they looked at them with fascination often mixed with exaggeration of how big carnivorous plants’ prey was.

In 1768, for the first time live Venus flytrap plants were brought from North America to England. In a 1770 book, John Ellis described them. He named the genus Dionaea, a Greek name for the goddess of beauty Aphrodite (Venus in Latin).

Venus fly-trap from Ellis' description

Ellis strongly suspected Venus flytraps were carnivorous. He wrote so to the most famous naturalist of the eighteenth century, Carolus Linnaeus, sending dried specimens with his letter.

However, Linnaeus did not believe that carnivorous plants existed.

Linnaeus, 11 August 2017

In support of that view, Linnaeus quoted the Bible, Genesis 1:30:

And to every beast of the earth, and to every fowl of the air, and to every thing that creepeth upon the earth, wherein there is life, I have given every green herb for meat: and it was so.

So, Linnaeus interpreted the Bible as saying that animals eat plants, not the other way round.

In this, Linnaeus was in a tradition, as pictured in this 17th century book, of seeing reality as a hierarchical ladder. God on top, humans below God. On the lower end, stones, etc. Plants one step below animals, forever unable to catch up with them.

Hierarchy, 11 August 2017

Linnaeus made tremendous contributions to systematic biology, still relevant today. However, comparable to earlier naturalists like Scheuchzer, he was still what would now be called a ‘creationist‘. He opposed the idea of evolution, in his own eighteenth century advocated in rudimentary form by Buffon, and later elaborated by Darwin, including as an explanation for the origin of carnivorous plants, as we shall see.

The poet Thomas Moore (1779-1852) reacted to the newly discovered Venus flytrap with the lines:

The Lord deliver us!
Think of a vegetable being “carnivorous!”

Venus flytrap, 11 August 2017

Now, from denial to fascination mixed with exaggeration.

Tree eating humans, 11 August 2017

In Victorian England, there were fictional stories, as well as stories claiming to be non fictional, about plants eating people; like a tree in Madagascar supposedly feeding on humans.

Today, we know that the biggest animals eaten by carnivorous plants are mice. And even that size is too much for most of today’s about 680 carnivorous plant species.

This video from the USA says about itself:

20 January 2017

While the carnivorous cravings of most flesh-eating plants are limited to small insects, one exception is the pitcher plant. It can consume anything that fits in its mouth–including a mouse!

However, Peeters said, twentieth century films like The Little Shop of Horrors and The Day of the Triffids continued the nineteenth century stories of carnivorous plants being dangerous to humans.

The little shop of horrors, 11 August 2017

Though about 1800 much was still unknown about carnivorous plants, they fascinated many people. Empress Josephine of France and President Thomas Jefferson of the USA owned Venus flytraps.

Since Darwin’s 1860s-1870s experiments with carnivorous plants, we know much more about the Venus flytrap.

Peeters illustrated that by playing this 2009 BBC video.

The video says about itself:

Life – Venus Flytraps: Jaws of Death – BBC One

Hungry Venus flytraps snap shut on a host of unfortunate flies. But, despite its name, flies aren’t the flytrap’s only meal. As long as its prey is roughly the right size and touches two of its hairs within twenty seconds, the plant will dine on any insect or spider that comes its way. Glands in the lobes then secrete enzymes that break the dinner down into a digestible soup. Ten days later, the trap pops open to reveal nothing but a dried out husk.

Thanks to Darwin and others, we now know more about the European carnivorous plant sundew than centuries ago.

Sundew has liquid droplets on it. Many other plants have dew droplets on them early in the morning. These evaporate as the sunshine gets stronger. In sundew, they don’t evaporate. People thought the sundew droplets were a peculiar kind of dew resistant to warmth; hence the plant’s name ‘sundew’.

Erasmus Darwin, 11 August 2017

In the late eighteenth century, Erasmus Darwin, the grandfather of Charles Darwin, said the sundew droplets were not dew. He correctly thought they had to do with insects. He did not know yet they had to do with eating these insects though.

Insectivorous plants, 11 August 2017

Erasmus Darwin’s grandson Charles experimented with carnivorous plants. In 1875, the results of these experiments were published in his Insectivorous plants. Why did plants become carnivorous? Because they grew in soils with few nutrients, Charles Darwin pointed out. They needed other sources of nutrients. In the course of evolution, carnivorous plants developed mechanisms to lure, catch and digest arthropod prey.

Sundew leaf, 11 August 2017

Like this specialized sundew leaf from Darwin’s book.

Carnivorous plants' traps, 11 August 2017

Peeters pointed out there are three kinds of carnivorous plants’ traps. Traps snapping tight, glue traps and pitcher traps.

The sequel of this will come on this blog. So, stay tuned!

‘Darwin’s Backyard’ chronicles naturalist’s homespun experiments. Breeding pigeons, growing orchids and other hands-on work provided evidence for the theory of evolution. By Sid Perkins, 10:00am, August 24, 2017.

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14 thoughts on “Carnivorous plants and Charles Darwin, lecture report

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