Have you noticed lots of small, biting flies lately? It’s blackfly season in the Georgian Bay Biosphere. Have you ever wondered where all these flies come from?

Mother blackflies lay hundreds of eggs in fast-moving, fresh water. The eggs hatch into larvae that live and grow in the water. The blackfly larvae look like bowling pins – they have wide bottoms and narrow heads. They live attached to plants or rocks in the stream, so that the fast-moving water doesn’t carry them away. While they are growing in the water, many of the larvae are eaten by fish, frogs, or other insects. The blackfly larvae that survive eventually encase themselves in an underwater cocoon, and transform into pupae (no longer larva, but not adult yet).

Have you heard the word cocoon before? Caterpillars also make cocoons before they turn into butterflies!

Blackfly Pupa in Cocoon Image: Sergey V. Aibulatov 2006
Blackfly Larva Anchored onto a Leaf: Seabrooke Leckie 2008

While they are in their cocoon, blackfly pupae grow legs and wings, and become adults. Then, the blackflies ride an air bubble to the surface of the water, so they can dry off their wings and fly. In order to lay more eggs and start the cycle over again, female blackflies need a blood meal! That is when we notice the flies swarming around and biting. The flies have been around all along though, in creeks, streams, and rivers where we can’t see them.

Like all creatures, blackflies play an important role in our ecosystem. Lots of different animals eat blackflies, and they are pollinators too! Luckily, there are some simple things you can do to reduce the number of bites you get while enjoying the outdoors.

  1. Wear long pants and sleeves. Blackflies are tiny and have a hard time getting through fabric.
  2. Wear light colours. Blackflies are more attracted to dark clothing.
  3. Visit Georgian Bay! Blackflies have a hard time flying when it’s windy, and don’t do well in open spaces. Lakes and meadows will have fewer blackflies than forests and streams.
  4. If you’re still getting bitten, you can try insect repellent.

Homemade Blackfly Repellent

Blackflies don’t like certain smells. Using a homemade spray with plant oils can keep them off short-term.

In a spray bottle, mix ½ cup of white vinegar, 1 tablespoon of dish soap, and 20-30 drops of essential oils. Some oils that blackflies don’t like are mint, pine, rosemary, basil, and lavender.

You can try different combinations to find a smell that you like!