Life Underwater Series: Life of the Leech

Date: April 1, 2019 Author: EcoSpark Categories: Latest

Life of the Leech: the benthic vampire

The leech is a fascinating benthic macroinvertebrate that can be a carnivore, detritivore but most often, parasite. Today we will explore the predatory nature of the leech and its life as a benthic dweller. How does the leech reproduce asexually and sexually? To explore this question and more, we’ll start at the very beginning-- when sexual reproduction occurs between two mates.

Leeches are hermaphroditic, meaning they have both female and male sexual reproductive organs, however these organs are not active at the same time in the life cycle so the quest for a mate endures. During mating, the sperm is transferred from each leech to the other and the fertilization will occur in both leeches in their female organ systems. Interestingly, leeches can also store their sperm and use it at an alternative time. Depending on the species, it can take anywhere from two days to several months after mating has occurred before the eggs are laid in the cocoon in the female reproductive system.

The eggs then hatch inside the leech and as juveniles they will feed on the nourishing albumen within the cocoon only to be released into the environmental when ready. Some parasitic leeches will have diets that consist only of invertebrate hosts, eating other worms, crustaceans and even other worms however, most of the parasitic leeches will feed on vertebrates including snails, frogs, turtles, birds and mammals including humans. Leeches feed by Leech2_resized.jpganchoring themselves to their prey and pressing their mouths and releasing an anesthetic while at the same time making incisions to desensitize the prey’s skin as it draws blood from it.

Fun Fact: With over 500 species of leeches they can be found anywhere in the world including marine, estuarine, freshwater and terrestrial ecosystems but not in Antarctica.

Fun Fact: In drought conditions leeches can burrow into sediment and construct a mucus-lined cell where they will lay dormant until water returns.

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.


Banks, B. (2014). Mystery Object. Retrieved from:

Nervous System. (2018). Leeches. Retrieved from:

Carina 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.