I think that it is safe to say that Darwin was fascinated, if not obsessed by carnivorous plants. In a letter to Asa Gray Darwin wrote:
This comment shows his remarkable ecological insight. By considering Drosera a ‘sagacious’ (i.e. wise) animal he recognised that they do more than just sit passively waiting for prey to stumble across them. More recently ‘active foraging’ for prey has been demonstrated in an excellent study by Aaron Ellison and Nicholas Gotelli where they showed that the shape of the pitchers of the Northern Pitcher Plant became less like traps and more like leaves when the plants had more nutrients (and so didn’t require the nutrients in their prey). This study, and a number of others add to a growing body of evidence that suggests that carnivorous plants can be ‘optimal foragers’ – they can alter their physiology and morphology to optimise the benefit of their prey. To put this in basic terms, they eat only when they’re hungry.
Darwin carried out numerous studies and experiments on a variety of carnivorous plant species, characterised by his usual attention to detail. These were presented in his seminal book Insectivorous Plants. This provided an excellent foundation for the next 150 years of research which was focussed on describing and understanding how carnivorous plants attract, trap and digest prey and what the benefit of that prey is. However, many questions remain. Why do they rely on nutrients from their prey? Do they regulate prey nutrient uptake in any way? How and why did carnivory evolve in plants? What is the ‘point’ of being carnivorous? In the Millett Lab we are attempting to address some of these unanswered questions. Carnivorous plants really are wonderful, but for me, turning trophic interactions on their head also makes them the most fascinating plants in the world.