Sundew lures select insects with its charms then polishes them off

by Emily Stone Naturalist/Educator Cable Natural History Museum


The sparkling drops of dew on the tips of the outer tentacles entice unsuspecting insect prey in for a sweet snack. Once stuck, the insects are digested by enzymes secreted from the shorter stalked glands. In this way, the tiny, carnivorous sundew can gain access to limited nutrients in a bog. --Photo by Emily Stone. The sparkling drops of dew on the tips of the outer tentacles entice unsuspecting insect prey in for a sweet snack. Once stuck, the insects are digested by enzymes secreted from the shorter stalked glands. In this way, the tiny, carnivorous sundew can gain access to limited nutrients in a bog. --Photo by Emily Stone. A pungent, earthy, vibrant aroma seemed to squirt out of the bog with every sinking footstep. Even through the soles of my muck boots I could enjoy the varying textures of this living carpet.

Soggy sphagnum moss offered almost no resistance, while the skeletons of tough twigs buried within the moss crackled, bent, and snapped.

At some point in each footfall, the cushion of living and dead plants pushed back toward me just enough so that I didn’t fall through.

Bogs are a unique, almost alien landscape, with a charm all their own. Funny plants, few trees, and a wonderful, squelchy, squashy, shaky, shivery, sucking substrate can turn adults back into giggly, wiggly kids. These twenty-two Wisconsin Master Naturalist Volunteer trainees were no different as they spread out to explore the Secret Bog.

Squatting down next to a domed hummock, I peered into a miniature jungle. Delicate vines of bog cranberry – with bright pink, swept-back petals on their tiny flowers; the wiry lattice of leatherleaf twigs; and bog laurel’s leaning stems with deep green leaves all poked their heads out of the mat of sphagnum moss like drowning rats.

Sphagnum moss may be the bog’s bully – pulling itself up on the stems of others, using woody plants like scaffolding – but it is also the reason that the bog is here.

Sphagnum’s primitive leaves are like tiny sponges, and can absorb up to 26 times their own weight in water. This can raise the water table. Such a saturated environment is low in the oxygen that microbes need to accomplish decomposition, so nutrients stay locked up in dead vegetation.

To deal with the lack of available minerals, sphagnum shoots hydrogen ions into its environment, dislodging scarce nutrients for its own use. This acidifies the bog, which further limits what plants can grow there.

Life is not easily discouraged, though, and a special suite of plants thrives in sphagnum’s world.

Peering over the side of the hummock, a sparkle caught my eye. Looking closer, I discovered a cluster of bright pink, hairy spoons, only an inch or two high. “Sundew!” I squealed, pulling over the nearest student naturalist to exclaim about it with me.

Round-leaf sundew are beautiful little plants, with a circumboreal distribution (around the Northern Hemisphere), and a penchant for animal flesh. Well, a taste for insects and spiders at least.

Sundews love the sunny, moist habitat created by sphagnum, but they still need to eat. Nitrogen is a limiting nutrient in bogs.

Some plants get their nitrogen through complex root systems and relationships with fungi, while others conserve it with the austerity of evergreen leaves. Sundews catch bugs.

The sparkle that caught my eye was actually a drop of “dew” clinging to the tip of a tiny tentacle. The bowls of sundew’s spoon-shaped leaves are dotted with these tentacles.

Long ones hold a drop of sweet, sticky nectar that attracts and entraps prey. Once an unsuspecting insect has been mired in this mucilage, the leaf curls inward.

This response to touch is known by the comical term: thigmonasty. From the bug’s perspective: thing most nasty.

Death usually occurs within 15 minutes, as the prey succumbs to exhaustion or is suffocated by the goo. Shorter tentacles, with drops of digestive enzymes at their tips, make contact with the prey and reduce it to nutrient-rich soup, which is absorbed through the leaf surfaces. The valuable nitrogen is use to make chlorophyll, enzymes, proteins, and seeds.

The seeds are produced in a delicate, white-petaled flower held aloft on a long stalk.

But how, might you ask, does the insectivorous sundew avoid eating its own would-be pollinators?

In nature’s wisdom, a completely different set of bugs is attracted to the flower from those who are lured in by the saccharine dew.

The group of students was lured in, too, a few at a time, to look at the impressive patch of sparkling leaves.

As we headed back to solid ground for our closing discussion, I plucked a little cluster of sundew leaves to bring in for a closer look.

At first I was annoyed when the tentacles stuck stubbornly to my finger. Then I chuckled at my own surprise.

It seems that Master Naturalists are no more immune than bugs to the cloying charms of sundew.



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