Spooky Stream Invertebrates of the Credit River Watershed

Celebrate Halloween with Underwater Creepy Creatures

At this time of year, when thinking of creepy creatures living in the Credit River Watershed, your mind might jump to spiders or bats, but some of the most fascinating creatures live beneath the surface in streams.

Each summer, we study stream invertebrates through our Integrated Watershed Monitoring Program (IWMP). This monitoring provides us valuable insights into the health of our rivers and streams and the ecosystems that depend on them.

Read on to learn about some aquatic creepy crawlies found in the watershed:

Hellgrammites (Corydalidae)

Hellgrammites, the larvae of dobsonflies and fishflies, live up to their fierce name because they are skilled predators with strong jaws and a surprising bite. Hellgrammites hunt at night beneath rocks in clean, fast-flowing streams, using the filaments along their sides as gills to breathe underwater. When they mature into dobsonflies, males grow long jaws to fight other males and to attract mates.

Giant Water Bugs (Belostomatidae)

Giant water bugs are among the largest aquatic insects, growing over 10 centimetres long. These fierce hunters use sharp mouthparts to inject digestive enzymes into their prey, earning them the nickname “toe-biters.” Giant water bugs can take down prey much larger than themselves, including tadpoles, small fish and even frogs. But they’re not all menace. Some male water bugs are devoted parents, carrying eggs on their backs until they hatch. If you spot one in your local waterway, take a moment to admire its remarkable mix of ferocity and care, from a safe distance.

Snail-case Caddisflies (Helicopsychidae)

Snail-case caddisflies larvae are ready for Halloween all year long. They disguise themselves by building spiral sand cases that look just like snail shells. These sturdy homes protect them as they live under rocks in streambeds, sometimes with a tiny door for extra shelter. So the next time you spot a “snail shell” in a stream, look closer because it might be an insect in disguise.

Leeches (Hirudinea)

Despite their spooky looks, leeches are among the most misunderstood creatures in our streams. Most don’t feed on human blood and some don’t feed on blood at all. Even those that do, they are clean feeders. They don’t spread disease like mosquitoes and ticks. Some leech species possess up to 10 eyes and can detect light, movement and vibrations to locate hosts. Species in the Glossiphoniidae family are devoted parents, carrying and feeding their young until they’re ready to venture off on their own.

Bloodworm Midge Larvae (Chironomus)

At first glance, these blood-red worm-like fly larvae might look alarming, but they’re harmless. The wiggling movements of bloodworm, or Chironomus, midges help stir up sediment, releasing nutrients that support other organisms in the ecosystem. Bloodworm midges get their colour from hemoglobin, the same oxygen-carrying protein found in human blood. This adaptation lets them survive in low-oxygen water, which is why they often thrive in areas with poor water quality, making them valuable indicators of watershed health.

Aquatic Invertebrates: Key Indicators of Stream Health

Through our long-term Integrated Watershed Monitoring Program (IWMP), we study aquatic invertebrates (insects, snails and crustaceans) as key indicators of stream health in the Credit River Watershed. Aquatic invertebrates help break down organic matter, cycle nutrients and provide food for fish, birds and other wildlife.

Next time you take an autumn stroll by your local creek, take a moment to appreciate all the life, both creepy and beautiful, wriggling beneath the surface.

Share your photos of invertebrates with us on Instagram, Facebook and X.

By Yael Lewis, Crew Member, Watershed Monitoring

• Environmental Monitoring
• Halloween
• Insects
• Integrated Watershed Monitoring Program
• Nature and Wildlife
• Watershed Health
• Watershed Science