How These Tiny Insects Teach us About the Health of our Waterways
On a summer night, you may have noticed swarms of tiny insects gathering around porch lights. At first glance, they look a lot like moths but often, they are caddisflies. Caddisflies are tiny insects that, as adults, spend only a short time on land. Instead, they spend most of their lives underwater as larvae.
While adult caddisflies live only briefly on land, their underwater life story can tell us a great deal about the health of local waterways. That’s why we monitor caddisflies and other aquatic organisms through our Integrated Watershed Monitoring Program (IWMP). These tiny creatures help us understand how stream conditions are changing across the Credit River Watershed and whether aquatic ecosystems are thriving.
Benthic Macroinvertebrates are Bio-indicators
Caddisflies, along with other aquatic insects, worms and crustaceans, are benthic macroinvertebrates. These are tiny aquatic organisms without a backbone that can be seen with the naked eye. Benthic macroinvertebrates are ‘bioindicators’, meaning their presence or absence signifies the health of our rivers and streams. These organisms vary in their tolerance to environmental stressors and can help us detect changes in water quality and ecosystem conditions within our watershed.
Caddisflies are Remarkable Builders
Not only are caddisflies important indicators of aquatic ecosystem health, but many species are remarkable builders. They create unique habitat structures, setting them apart from other benthic organisms. Streams containing abundant and diverse caddisfly communities are often a sign of cool, clean, well-oxygenated water. These characteristics are important in maintaining Ontario’s native fish populations.
Underwater Larval Living
Caddisflies begin their lives as aquatic larvae and fall into one of three groups: case-makers, net-spinners or free-living caddisflies.
Case-making Caddisflies
Case-making Caddisflies, such as the long-horned caddisfly, produce silk to fuse materials together into a protective case. These cases provide shelter and protection from predators and fast-moving water, while allowing water to flow over their gills for breathing. Cases can vary in shape, size, and building material depending on the species. Materials can include sand, rocks, leaves, twigs, and empty snail shells. The larvae use small hooks on their hind legs to anchor themselves inside their cases as they move along the streambed in search of food.
Net-spinning Caddisflies
Net-spinning Caddisflies, such as the common netspinner, act as ecosystem engineers. Using silk, they build net-like structures between rocks that filter and capture small food particles. These structures can help stabilize small areas of streambed and create microhabitats for other aquatic organisms. In these stable environments, net-spinners can use their silk and other small particles to build themselves a ‘protective retreat’ shelter, where they can safely rest away from fast flowing water.
Free-living Caddisflies
Free-living caddisflies do not build cases or nets. Instead, they crawl on the streambed in search of food, using hooks on their legs to latch onto rocks in fast-flowing, well-oxygenated streams.
From Larvae to Adult
Once the caddisfly larvae have completed their larval stage, they craft and seal themselves inside a protective casing and enter the pupal stage.
Once development is complete, the pupae use specialized mouthparts to cut their way out of the case. They then emerge from the water and transition into an adult, completing the final stage of metamorphosis.
The adults then take flight, reproduce, and lay eggs in or near a stream to begin the cycle again.
Why Caddisflies Matter
Although they are easy to overlook, caddisflies provide valuable clues about the condition of our rivers and streams. Their diversity, abundance and sensitivity to environmental change make them one of the many indicators CVC uses to assess watershed health.
Every benthic sample collected helps us build a long-term record of environmental conditions across the Credit River Watershed. This information supports watershed planning, habitat restoration, water management and conservation efforts that help protect local ecosystems for future generations.
The next time you spot a moth-like insect circling a porch light on a summer night, take a closer look. It might be one of nature’s smallest architects and one of our most valuable partners in understanding the health of our waterways.
Learn more about how CVC collects and monitors environmental data, including benthic macroinvertebrates, through the Integrated Watershed Monitoring Program.
By: Ally Melanson, Crew Member, Watershed Monitoring (Benthos)