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Posted by: Kirsten Pisto, Communications

Stepping into the greenhouse at Woodland Park Zoo, I am hit with a hot, humid air that smells of fertilizer, earth and some wildly primal perfumes. In the farthest corner is a table smothered in a muddle of vines, twisting tendrils and mysterious red and pink flanked vessels. Welcome to the land of the endangered old world pitcher plants, Nepenthes.
A dangerous view for a curious insect, the vibrant red lip on this pitcher plant is both tempting and deadly.

I tracked down Woodland Park Zoo gardener and pitcher plant enthusiast, Justin Schroeder, who had a lot to say about these endangered carnivores.

Old world pitcher plants live in very remote areas, deep in the hillsides of tropical Asia. They prefer sunny ridges and slopes to thick jungles. Rain and high humidity are important elements of their environment as they like a permanently wet soil. Old world pitcher plants can grow epiphytically, atop other plants, trees or logs, and can climb to the tops of the highest canopies or make their space on the dark forest floor.

The pitchers are a modified part of the leaf. Not all the leaves have pitchers, but some of the leaf tips will balloon into a hollow, sealed pitcher. When the pitcher is mature, its top will pop open forming a lid. Then bristly ladders emerge along the front of the pitcher.

Pitcher plants often grow in acidic soil, between shallow leafy debris and gravely seeps, where a lot of the nutrients that would otherwise be available are swept away with the moving water. So what is a plant to eat?

Carnivorous, the tropical pitcher plants lure their dinner by offering their sweet nectar to unsuspecting prey. The pitchers themselves are an intricate trap, designed to digest enough insects to keep them well nourished. The different parts of the trap all work together to ensure that insects won’t escape.

Here you can see the ‘ladder’ that allows insects an easy route to the rim of the pitcher.

The entire plant is covered with nectar glands, but the nectar is thicker along the tendrils, the ladder, the peristome (lip), and under the lid. The lid itself acts as a little umbrella to stop rainwater from diluting the digestive juice deep inside the trap.

The pitchers vary greatly, even on the same plant. Some of the low hanging pitchers are short and squat, with more ladders for ants and crawling insects. The pitchers which climb up higher entangle themselves onto vines and are often more elegant and funnel shaped to lure winged insects.

The bright colors of the pitchers as well as the succulent nectar lure the insects, mostly ants and gnats to the underside of the lid. The nectar is a bit like a shot of tequila; some ants appear intoxicated after feeding for a while, spinning around in circles and falling from the lid into the deep pitcher.

The syrupy nectar attracts all sorts of insects and small mammals to the peristome (lip) of the plant.

Once inside the pitcher, insects have few options. The upper part of the pitcher’s waxy slope is nearly impossible to climb. The lower digestive zone is covered with hundreds of large glands that secrete a killer juice. The juice liquefies the soft parts of the prey right away. The enzymes can digest a fly in a few days, and then the glands reabsorb the soup. There is often a pile of insect corpses at the bottom of the trap, an exoskeleton graveyard. It sounds gruesome, but a plant has got to eat.

Each pitcher has a built in springboard that launches the punch-drunk insects onto a sort of slip and slide death trap. The insects then slide down this waxy-walled slope into the deepest part of the pitcher. Here you can see a pile of drowned gnats.
Thank goodness there aren’t giant pitcher plants…but wait, there are! The largest pitcher plants in the world, Nepenthes rajah, are able to capture animals as large as rats. Yikes and eww!

Many nepenthes host a rainbow of colors and are popular with florists.

Okay, so enough villainizing. Justin tells me these plants do have a sweet side. Many creatures have a loving relationship with Nepenthes, including people. Let’s count the ways…

  • They provide water for ant colonies during times of drought (sure, they may digest one or two in the process, but tit for tat.)
  • Golden ants actually raise their young in holes they drill into the tendrils of the N. bicalcurata. (Such a good babysitter!) 
  • Drummer ants claim pitcher plants for their own and beat their abdomens on the lids of the pitchers to scare off intruders. (Drummer ants are immune to the digestive juices, but it’s not clear why.) 
  • Red crab spiders attach themselves to the inside of the trap by a small thread and swing into the pitcher to snatch up flies and fish for mosquito larvae (literally fly-fishing). Even cooler, the crab spider will leap into the juice if it is threatened and actually pull itself out again on its safety web.
  • Humans have used the pitchers for carrying rainwater (even insect soup is refreshing in parts of the tropics!) 
  • People have used pitcher plants for numerous medicinal uses, including: eyewash, asthma reliever, painkiller during childbirth, skin burn, reducing fever, indigestion, heartburn, and dysentary 
  • The stems of some pitcher plants, N. ampullaria, were once used to bind fences and are thick as ropes 
  • Rice is even cooked in some of the larger pitchers. (Nothing like a little extra ant carcass in your rice!) 
  • This pitcher plant allows the woolly bat to roost in its leaves. While the bat sleeps securely in his pitcher plant nest, the plant traps the bat’s droppings and gains nutrients and fertilization. This plant might be a toilet for the bat, but the vital nutrients are well worth the price. 
  • A similar agreement exists between the treeshrew and the pitcher plant, Nepenthes lowii. The plant supplies sweet nectar at the rim of its lid where the treeshrew can easily lick off any excess sugar, and whenever the shrew needs to poop, the pitcher plant gets its own little treat.

There are about 80 species of tropical pitcher plants and most all of them hail from Borneo, although isolated populations are found as far off as Madagascar and New Caledonia. These plants are vulnerable due to their shrinking habitat and urban encroachment.
Justin says the pitcher plants at Woodland Park Zoo each catch about one hundred gnats every night! He waters these puppies daily and makes sure they have a nice fertilizer foliar spray to their leaves. Pitcher plants can live ten to twenty years, most of ours are about ten years old. Our collection of pitcher plants was donated to the zoo from the University of Washington Botany Greenhouse.

The greenhouse and horticulture bungalow, tucked away at the edge of the zoo, are significant players in supporting the daily operation of the zoo and our animals’ wellbeing. Understanding the flora and fauna of a landscape allows biologists and researchers to better protect both the endangered plants and animals of each biodiverse region.

On zoo grounds, you can find pitcher plants in the Tropical Rain Forest building and in Zoomazium. Happy gnat hunting!

All photos by Kirsten Pisto/Woodland Park Zoo.

Works referenced: D’Amato, Peter. The Savage Garden: Cultivating Carnivorous Plants. Berkeley: Ten Speed Press, 1998. Print.


Unknown said…
Great article! One of the favorite things we see on the Real close Tour!