Cambridge Festival Speaker Spotlight

Charlotte Andrew is a PhD student in the Insect Biomechanics Group in the Department of Zoology. Her research explores the mechanical implications of weather conditions on insect trapping in carnivorous plants.

Charlotte will be speaking about her PhD research on the devious ways in which Nepenthes (tropical pitcher plants) attract and capture their prey and her fieldwork in Borneo at the event Charles Darwin and Carnivorous Plants at 150 (29 March, 2pm)

Tell us about your research and why it is important.

My research focuses on two types of carnivorous plants: Nepenthes pitcher plants and Sundews (Drosera) that have very different methods for capturing insects, which they rely on to gain essential nutrients. Pitcher plants form cup-like leaves which have a rim that can be very slippery to insect feet and contain a deadly pool of digestive fluid inside which traps the unsuspecting insects that fall in. In contrast, sundews employ small droplets of very sticky capture fluids, suspended by hairs on their leaves, insects that attempt to walk over the leaves will become stuck and eventually digested by the plant.  

What these two types of plant have in common, is their use of fluids to capture insect prey. In my research, I take a mechanical approach to investigating how the trapping functions of the fluids in these plants are affected by weather conditions. For example, heavy rainfall may dilute and flood the plants’ digestive fluids, washing away captured prey and rendering them ineffective at trapping any more insects. Conversely, during hot and dry weather periods, these insect-trapping fluids may evaporate, thus preventing the plant from capturing prey.

So, how are carnivorous plants’ able to cope with the effects of the weather conditions in their environments? By performing experiments both in the field in Borneo and in the lab here in Cambridge, I have been able to uncover the amazing ability of Nepenthes pitcher plants to remove excess water after rainfall and secrete more fluid after evaporation in order to maintain their pitchers as effective insect traps. While the fluids on the leaves of Drosera plants seem to be much less strongly affected by weather conditions, they are able to replenish their fluid droplets after they are removed.

It is important to assess the resilience of these plants’ ability to trap insects under different weather conditions as the effects of climate change worsen, and extreme weather events such as heavy rains and drought become ever more abundant.

What exactly is a carnivorous plant and what makes them special?

A carnivorous plant is one which gains some or all of its nutrients via the capture and digestion of other organisms. Their prey mainly consists of microorganisms, insects and other arthropods but can even include small mammals and birds! Being carnivorous and not relying on the soil in which they grow for nutrients, allows these plants to grow in areas where little else can flourish and as such they can be found on all continents except Antarctica!

Carnivorous plants come in many shapes and sizes and use a variety of strategies to capture prey from the snapping traps of the Venus fly trap or pitfall traps in hundreds of species of pitcher plants to suction traps in bladderworts and sticky fluids on the leaves of sundews and more, carnivory really is an effective and fascinating mode of survival for over 600 plant species.

Tell us a fact you’ve learnt during your research which would surprise us.

There are a surprising number of animals that are not trapped by pitcher plants but rather use them in unique ways. For example, there is a species of bat (Hardwicke’s Woolly Bat) that uses the pitchers of Nepenthes hemsleyana as a roost- they fly head first into the pitchers and sleep during the day with their feet sticking out the top! There are also some pitcher plant species that attract small rodents by secreting nectar and while the rodent is visiting to enjoy a tasty meal, it uses the pitcher has a toilet and deposits its excrement into the trap, giving the pitcher a not so tasty meal in return!

What do you think Darwin would think about how far research has come in the last 150 years?

The works of Charles Darwin’s Insectivorous Plants focus predominantly on plants of the then Droseraceae family (inc. sundews and Venus fly traps) as well as bladderworts. It is clear that Darwin found great fascination in the carnivorous plants he studied, even writing: ‘I care more for Drosera than the origin of species... it is a wonderful plant, or rather a most sagacious animal. I will stick up for Drosera to the day of my death.’ in a letter to Asa Gray.

While Darwin was familiar with many forms of carnivorous plant, relatively little was known about their incredible strategies for insect-capture compared to today’s knowledge and I’m sure the discovery of the wonderful symbiotic relationships these plants have formed with other animals would have delighted him. Moreover, Darwin definitely would be pleased to hear that the American pitcher plants (Sarracenia) that he never had a chance to study, are indeed carnivorous as he suspected!

What’s your favourite insect and why?

I think I would have to say stick insects. They are the ultimate masters of disguise and the range of different colorations, shapes and sizes that how they camouflage themselves in different habitats is truly remarkable. They were also the first insects I ever worked with, and their docile, friendly nature made them by far the easiest to handle of all the species I have worked with!

What’s the one takeaway you would like people to take from your talk?

Life might seem easy for a carnivorous plant, sitting and waiting for insect food to come to them. But there is in fact a number of contrasting requirements these plants have, in turn this means that they maintain finely-balanced strategies to overcome these challenges. For example, how can a carnivorous plant reproduce without pollination? The plants have to avoid capturing helpful pollinators while still trapping enough food to survive. For this, many carnivorous plants house their flowers on long stalks, as far from their traps as possible to separate pollinators from prey.

Another example is many carnivorous plants’ need for an abundant water supply to their roots but the detrimental effect of too much rainwater on their traps. These plants often live in marshy areas with frequent rainfall and must therefore actively maintain their traps by absorbing and secreting fluid to remain effective at capturing insects. So it takes a significant amount of effort to be carnivorous but still perform ‘normal’ plant functions!