Nature Nugget: Carnivorous Sundew Plant Often Robbed of its Catch

Sundews have a tough life in the peatlands.

Welcome to the wetland

Step (carefully) into one of Vermont’s peat wetlands, such as a bog or a fen, and time seems to slow down. Beneath your feet may be several meters of peat—partially decomposed plants like mosses, sedges, and shrubs—that is thousands of years old. A lack of oxygen prevents this material from breaking down completely, preserving it for millennia and building up the surface of the wetland over time. Peatlands store carbon more effectively than any other natural systems on earth.

While Vermont’s bogs and fens may look uniformly mossy at the surface, a closer look will likely reveal several species of Sphagnum and other mosses, subtly varying in color, texture, and shape. Look even more closely and you might spot a tiny and fascinating plant sparkling amid the moss: a sundew.

How do sundews feed?

Vermont’s two species of sundew—round-leaved sundew (Drosera rotundifolia) and spatulate-leaved sundew (Drosera intermedia)—are beautifully deadly. Leaves covered with delicate “tentacles” emerge on needle-like stalks from a central base, looking like minuscule fireworks caught mid-burst. The tentacles produce a sticky substance, and these shiny droplets attract and trap insects, which the plant then digests.

Researchers have found that sundews in the wild get about half of their nutrients from insects and the rest from the soil or peat. Essential plant nutrients like nitrogen are lacking in peatlands, so sundews and other carnivorous plants like pitcher plants fill the gap with insect prey. However, sundews growing in the shade produce less of this mucus-like carbohydrate—and are less sticky overall—than those in full sun. Why? Sunlight completes photosynthesis, the chemical creation of sugars from carbon dioxide and water. With less of it, sundews seem to ‘invest’ less in making the more complex carbohydrate used in the sticky insect traps.

Getting along with the neighbors

The boggy drama doesn’t end here. Though a spiky, sticky leaf in a sunny spot may trap lots of small insects, it’s still no guarantee of a meal for the plant. One scientist found that bog-dwelling ants rob round-leaved sundews of up to 70 percent of their trapped flies. Other researchers have described competition between sundews, spiders, and toads for the same insect prey. And many sundews still rely on insects to pollinate their flowers, which rise safely above the treacherous leaves to avoid trapping valuable pollinators. It’s a tough world out there—make sure you pack your own snacks for your next peatland sojourn.