Life After Water Series: Life of the Black Fly

Date: November 21, 2018 Author: EcoSpark Categories: Latest

Life of the Black Fly: The Lactic Acid Detector

The blackfly is a fascinating benthic macroinvertebrate that thrives in running clear, unpolluted water bodies. Today we will explore what happens after the blackfly pupae leaves the safety and familiarity of the water? And how does the blackfly pupae transform into its adult form? To explore these questions, we’ll start at the very beginning-- when the blackfly eggs are first laid.black1.png

 The female blackfly will lay anywhere between 150 to 600 eggs on vegetation, various substrates such as rocks and other stream debris or even atop the surface of running water bodies. When the eggs hatch as larvae, they will attach themselves to rocks and vegetation and will complete their development across the span of 3-14 days. This exact amount of time will depend on temperature and the availability of food. Their diet at this point consists mostly of algae and small organic particles.

 From the larvae stage, the blackflies will then enter the pupae stage as the water temperatures increase. During this phase, there are inactive and do not feed. Following, they develop into adults as they emerge from any depth of the water column in a bubble of air, ready for flight upon reaching the surface. 


 In their adult form, their life span is approximately 3 weeks, allowing time only for mating, after which the male will go off in search of nectar required for flight energy and the female in search of blood to help lay her eggs. Females will find their blood meal by following a scent trail of carbon dioxide combined with body heat as they are attracted to dark moving objects and lactic acid. The likely prey can include animals, birds and of course humans. A blackfly is known to travel up to 16 km for a meal. Once fed, the female blackfly will return to the same stream and lay her eggs.  Typically, blackflies emerge mid-May and will die off after the spring creek run-off has ended.

Fun Fact:  There are 165 species of Blackflies in Canada alone but only two of these species bite.

 Fun Fact:  Although they are called blackflies there are approximately over 1,800 of different colorations in blackflies worldwide. Interestingly, the ones that tend to bite humans are black in colour.

 Interested in learning more about benthic macroinvertebrates and how they can be used to measure the health of rivers and streams? Be sure to follow EcoSpark’s social media to stay updated on our Changing Currents program and our other citizen science and environmental education programs.


Blackflies. (2018). Mosquito Magnet. Retrieved from:

carina.pngCarina is an Environmental Education Assistant with the Changing Currents Program at EcoSpark. She is passionate about aquatic ecosystems and educating young minds on the connections between land and water. She recently graduated with a degree in Environmental Studies from York University and a diploma in Ecosystem Management Technology from Sir Sandford’s Fleming College, School of Environmental and Natural Resource Sciences.