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10 Oct 2018

Plants with Bite: sticky, sneaky & freaky

Insects are lured with promises of sweet nectar, delightful smells and captivating colours by murderous munchers in the plant kingdom. But it’s always too good to be true for the unsuspecting prey as they find themselves trapped, stuck or slipping to their certain death. 

What makes a plant a killer?

There are more than 800 recognised species of carnivorous plants. They can be found in 11 different plant families and vary widely in appearance and size. The only thing they all have in common: THE NEED TO KILL.

To be defined as carnivorous, a plant must first have a trait that is specifically for the attraction, capture and digestion of prey. The second requirement is the ability to absorb nutrients from dead prey and gain an advantage from the integration of these nutrients.

Unlike other plants that get their nutrients from the soil and by forming sugars through photosynthesis, carnivorous plants have evolved to get theirs from insects. Amazingly, they have adapted to grow in places where the soil is thin or low in nutrients, especially nitrogen.

While death and dinner are the same for all carnivorous plants, keep reading below to learn about the different tactics they use to lure, trap and trick their prey.

Snap traps – fast and furious

This is perhaps the most well-known trapping mechanism of carnivorous plants, made famous by the Venus Flytrap (Dionaea muscipula). This trapping technique has also been described as a ‘mouse trap’, ‘bear trap’ or ‘man trap’, due to its shape and rapid movement.

It has leaves with a terminal section divided by two lobes, hinged along the midrib. Inside are trigger hairs and when two are bent by a visiting insect within 20 seconds, the trap snaps shut. While the mechanism of how exactly this happens is still debated, the whole process takes less than a second for a Venus Flytrap.

Further stimulation of the trigger hairs by the struggling victim then causes the lobes to close even tighter. This forms a kind of stomach, activating digestive enzymes so digestion can take place over a period of one to two weeks.

Flypaper traps – slimy and sticky 

Another strategy that killer plants use is using sticky mucilage or glue to trap their prey. One genus who has perfected this art is the sundew (Drosera spp.), which consists of over 240 species whose mucilage glands form droplets at the end of long tentacles.

It was an astonished Charles Darwin who scientifically confirmed that plants could capture and digest prey. In 1860 he wrote: I care more about Drosera than the origin of all the species in the world.

Some sundews like Drosera capensis can bend their tentacles up to 180 degrees in a minute or so in response to the trapping of an insect. Sundews are found on all continents except the Antarctic mainland, but Australia has the most diversity on Earth with close to 100 species.

An insect being trapped by a sundew (Drosera spp.). 

Pitfall trap – slow and slippery  

A pitfall trap is more passive and is characterized by an internal chamber that attracts prey with nectar bribes secreted at their opening. The ‘pitcher’ structure is often thought to be a flower, but it is actually a modified leaf!

The genus Nepenthes has a unique design called a peristome, an anatomical feature that surrounds the opening to the pitcher. The peristome is either slippery when wet or when dry, but rarely both. The upper lining of most Nepenthes pitcher plants are covered in a loose coating of waxy flakes which are slippery for insects, causing them to fall into their slow and certain death after sampling some delicious nectar.

Other pitcher plants, such as Sarracenia and Heliamphora, have downward pointing hairs that make escape virtually impossible. As the victims struggle, digestive enzymes start to break down the prey into an absorbable form for the hungry plant.

Sarracenia leucophylla is a type of pitcher plant. 

Greg Bourke: Carnivorous plant hunter

Greg Bourke is the Curator Manager at the Blue Mountains Botanic Garden and is one of Australia’s leading experts on carnivorous plants.

His passion for understanding, discovering and cultivating carnivorous plants started when he had his first encounter with killer plants when he was just four or five years old.

He’s been all over the world in search of murderous munchers, including the wetlands of the Northern Territory, Malyasia, the Philippines and Indonesia.

“It’s an addiction. After seeing the madness and unique design of the flesh-eating fiends on the television screen, I was hooked,” Greg said.

“What attracts me more than anything else is getting out there and trying to find a rare or difficult-to-find species, seeing it in the wild, documenting and learning about it.

“To find and see a new species in the wild is up there with the birth of my first child. It’s just awesome,” said Greg.

Greg is also one of the authors behind an encyclopaedic book series called 'Drosera of the World', documenting the knowledge to date of sundews. 

Carnivorous plant expert and Curator Manger at the Blue Mountains Botanic Garden, Greg Bourke.

The Australian bushland is teeming with a cycle of death, dying and digestion and every plant has a story to tell.
Greg Bourke, carnivorous plant expert.

Behind-the-scenes at Greg’s killer plant collection

In this Plants with Bite podcast episode, Branch Out host Vanessa Fuchs saw Greg’s incredible private collection of carnivorous plants from all over the world.

“While I was interviewing Greg in the Blue Mountains and entering green house after green house of amazing specimens, a native bee got trapped right before my eyes inside a pitcher plant,” said Vanessa.

“You can hear the dreadful buzzing as it struggles to escape right at the beginning of the Plants with Bite podcast episode.

“I felt so helpless and was tempted to help it escape, but I knew I had to let nature take its course,” Vanessa said.

Just a fraction of the carnivorous plants Greg Bourke has in the Blue Mountains.

Plants with Bite exhibition at The Calyx – enter if you dare

Also featured in the Plants with Bite podcast is the Horticulture Director at the Royal Botanic Garden Sydney, Jimmy Turner. Jimmy is the creator and visionary behind the largest interior green wall in the southern hemisphere at The Calyx and the current Plants with Bite exhibition that just opened.

“I wanted a massive green wall that could be changed for different exhibitions. I see it as the Broadway stage for plants!” said Jimmy.

“We planned the Plants with Bite exhibition for over 18 months and it is the fourth floral display to hit The Calyx.

“With educational and spooky ‘feeding days’ for kids, this freaky exhibition allows visitors to get up close with beautiful and deadly carnivorous plants of the world,” said Jimmy.

The current Plants with Bite exhibition includes a colossal collection of about 7,000 carnivorous plants. Feast your eyes and sink your teeth into the free Plants with Bite floral display between 10am to 4pm daily at The Calyx.

Hungry for more?  

Join Greg and Jimmy and go deep into the world of freaky carnivorous plants in the Plants with Bite podcast episode below.

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Photos: Greg Bourke

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