Don Lyman
Boston Globe October 27, 2023
Sundews and pitcher plants are found in bogs across Massachusetts.
Round-leaved sundew plants the author found in the Pine Hole Bog in Andover. The sticky hairs trap tiny insects and other invertebrates that the sundew then digests. DON LYMAN
When I teach ecology labs at Merrimack College, one of my favorite places to take students is the Pine Hole Bog in Andover’s Charles W. Ward Reservation. While walking along the quarter-mile boardwalk that traverses this fascinating wetland, I point out the many interesting plants that grow in the bog — wild cranberries, horsetails, poison sumac, sphagnum moss, swamp loosestrife, and others.
But perhaps the most interesting are the carnivorous plants — sundews and pitcher plants — that are found here and in other bogs across Massachusetts.
While walking through the bog recently, I crouched down on the edge of the boardwalk and closely scanned the vegetation along the ground. There, hidden among the sphagnum moss and red maple seedlings, I spotted a cluster of 2-inch-tall plants, with single small green disc-shaped leaves on top of their stalks. Each leaf was covered with tiny hair-like projections, with sticky drops that looked like dew at the tip of each hair. These were round-leaved sundew plants, one of three species of sundews found in Massachusetts.
The others are the spatulate-leaved sundew and the thread-leaved sundew, said Professor Aaron Ellison, retired Harvard University senior research fellow in ecology and associate of the Harvard Forest in Petersham. Ellison, who co-edited a book on carnivorous plants, said small insects — such as gnats and mosquitoes — that land on the sticky hairs often get trapped. The hairs fold around the insect, which is subsequently digested by enzymes.
Nutrients from the digested insects are absorbed by the leaf pad.
There are also 12 species of bladderworts — a type of aquatic carnivorous plant — found in Massachusetts, said Ellison.
A purple pitcher plant in the Pine Hole Bog in Andover. DON LYMAN
I continued walking slowly along the boardwalk, stopping periodically to peer into the thick vegetation, searching for purple pitcher plants, which I hadn’t seen in several years. I walked to the Pine Hole Pond at the end of the boardwalk, then started walking back. I continued looking into the brush, scanning the ground carefully as I walked. Suddenly, there they were — pitcher plants.
The leaves of pitcher plants are 4 to 10 inches long, and shaped like narrow pitchers, partially filled with water, hence their name. If insects or other small invertebrates enter the pitcher plant, they sometimes can’t escape because downward-pointing bristles at the opening of the “pitcher” block their exit.
“But it’s not a very efficient barrier,” said Ellison. “Pitcher plants trap mostly ants, which are attracted to sugar secreted by the plant. Ninety percent of the ants that crawl into a pitcher plant crawl out.”
The water in the pitcher plant contains a food web of bacteria, protozoa, and aquatic insect larvae, which help break down and digest insects that fall into the plant’s watery trap — kind of like the bacteria in our intestines that help break down and absorb the food we eat, Ellison explained. The nutrients from the digested insects are then absorbed by the pitcher-shaped leaf.
Amazingly, some insects can live in pitcher plants. One of these is the pitcher plant mosquito, the larvae of which hatch, live, and metamorphose in the water inside the pitcher plant without being digested.
Despite their name, not all purple pitcher plants are purple, said Ellison. Some are a mix of red and green, while some — like the ones I found — are just green. The more sun they’re exposed to, the more purple they are, Ellison said, because they produce anthocyanin, the same pigment that’s in red fall leaves. The anthocyanin works like a sunscreen for the plant to prevent sun damage.
Sundews and pitcher plants are only found in bogs, a nutrient-poor environment with low amounts of nitrogen and phosphorous, Ellison said. Carnivorous plants supplement the small amount of nutrients they absorb through their roots with the insects and other invertebrates they capture.
The flowers of pitcher plants are pollinated by bees, such as bumblebees, said Ellison, while sundew flowers are pollinated by little solitary bees, like metallic green sweat bees.
Sundews and pitcher plants face few natural threats, said Ellison, although the caterpillars of some moth species feed on pitcher plants. The greatest threat to carnivorous plants is habitat destruction and collection by people.
“If you want carnivorous plants, buy them from a reputable dealer,” said Ellison. “Don’t collect them from the wild.” They won’t really help with mosquito control in your yard, he added.
People always like to try to feed them pieces of hotdogs or hamburger meat,” said Ellison. “Just put them out in the sunlight during the warm weather, and let them catch insects. Then let them go dormant for the winter by putting them in the refrigerator or a cold garage for six months. Bring them back out in spring and water them. If you don’t feed or fertilize them, they can live a long time — pitchers 70 to 80 years, and sundews 10 to 20 years.”
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