For most people, a hellgrammite is not the sort of creature they hope to find in a stream.
The larvae, which grow into winged dobsonflies, can reach 3 to 4 inches long. They have large heads, sharp pincers, and small claws on the tips of their six legs. They hide under rocks in running water, and their pincers can startle anyone turning over stones.
But in the shallow waters of Wappinger Creek, the discovery of hellgrammites was good news: Because they need clean, well-oxygenated water to survive, their presence can be a sign that a stream is healthy.
On the morning of June 20, about 30 conservation enthusiasts gathered at the Gary M. Lovett Wildlife Preserve in Stanford to look for hellgrammites and other aquatic macroinvertebrates — small insects that don’t have a backbone and are visible to the naked eye.
The event, a rapid biological assessment, was organized by the town’s Conservation Advisory Council and led by one of its members, biologist Diane Duffus. By the end of the morning, the group had found several other pollution-sensitive species, including mayfly nymphs, with their three distinctive tails; stoneflies, with long antennae and two tails; and water pennies — tiny, flat, brown discs that cling to rocks.
Together, Duffus said, the macroinvertebrate sightings indicated that the stretch of the creek, just a few steps past the meadow, was in good condition.
“Some are highly sensitive, some are semi-sensitive and some are tolerant,” Duffus said. “The ones that are the most desirable to find are the ones that are highly sensitive because if there was pollution here, they wouldn’t be. When we find them in abundance, and in some cases we did, that tells a very positive story.”
Although Duffus found a couple of caddisfly larvae, which are also intolerant of pollution, adult caddisflies were harder to spot. They build tiny shelters from silt, sand, pebbles, and sticks that they carry on their backs wherever they go and are masters of camouflage.
There were also about 40 to 50 crayfish, which are considered moderately tolerant of pollution. The absence of leeches and mosquito larvae, which are more commonly found in degraded water, was also encouraging.
Natalie O’Malley, a fellow CAC member, described the macroinvertebrates as “canaries in a coal mine” — early warning signs that reveal the condition of a waterway.
Attendees wore rain boots or waders and used a variety of nets and strainers to collect the insects. They worked in pairs: One held the net while the other acted as the stream dancer, as Duffus called it, gently disturbing the pebbles to dislodge the animals hiding beneath. They used plastic spoons and paint brushes to ease the creatures from the net into buckets to observe, then placed them back into the creek after identification.
“The great thing about this kind of work is that a lot of the materials are very accessible,” O’Malley said. “Science isn’t something that’s just a high-in-the-sky activity.”
Duffus encouraged residents to try the method on any lakes or ponds near their homes. Periodic assessments can help keep local water bodies healthy, she said, noting that testing the same spot everyday risks disturbing the creatures’ habitat. She also urged everyone who enjoys visiting the preserve to pick up after their pets, a small but meaningful step toward keeping the watershed clean.
Although the portion of the creek running through the preserve showed signs of clean water that morning, it flows year-round through largely agricultural land, making it susceptible to nonpoint sources of pollution. These include runoff, animal waste, and other contaminants that are difficult to trace to a single origin and risk reaching the groundwater that residents drink.
Only a few miles south, the picture is starkly different. The 2-mile stretch downstream of Wappinger Falls, extending into the Hudson River, was designated a Superfund site by the Environmental Protection Agency in 2016. A nearby industrial park contributed to decades of contamination from textile dyeing and other commercial activity, leaving the water severely polluted — a reminder of how humans can adversely impact the natural resources around them.
“Water is almost always on the move, whether it’s on the surface or in the ground,” Duffus said. “Clean water is needed for all organisms’ survival, ourselves included. So really, it’s imperative for each of us to be good stewards of our land and water.”