The interesting world of leeches!
Written by Avalon Carthew, First Nations Conservation Technician
Do leeches suck? Yes, and no. They certainly aren’t as beautiful as a green-winged teal or as adorable as Blanding’s turtle. Oh, and that whole “blood drinking” thing is pretty unappealing to many people, too. Leeches have an important job to do, and do it they shall, despite what us humans may think! By highlighting the unique relationship that turtles and leeches have, I hope you gain a new found appreciation for these creatures and their role.
An Introduction to Leeches
Leeches are worms, but unlike earthworms, leeches have a sucker at each end of their body. One is for moving, and the other is for eating. There are over 700 species of leeches in the world, and they aren’t all blood drinking, or sanguivorous, parasites. In fact, about half of leeches eat insects, snails, or even fish eggs (Phillips et al, 2020)!
Leeches breathe by absorbing oxygen through their skin, similar to some amphibians. They are hermaphrodites, so each leech has both male and female reproductive organs. One leech will attach a capsule of sperm called a spermatophore to its mate. The sperm will then travel through the skin of the other leech and make its way to the ovaries. Wow!
While leeches are commonly thought of as aquatic animals, North America is home to three species of leeches that live on land (Wirchansky and Shain, 2010)! Haemopis terrestris is one such leech, which can be found in states such as Illinois and Indiana. They eat earthworms and even smaller leeches of their own species (Hiebert, 1974).
Every animal has a special role to play, and leeches are no exception. Leeches are a source of food for animals such as turtles, birds, and fish. As predators, they keep populations of mollusks and insects in check (Bolotov et al, 2019). Leeches are also good indicators of water quality, such as amounts of dissolved oxygen and dissolved nitrogen (Cortelezzi et al, 2018).
Leeches aren’t just important members of the food chain; they also have a role to play in medicine! Leeches have been used for medicinal purposes as far back as 1500 BC in Egypt (Munshi et al, 2008). Today, this practice is called hirudotherapy. It involves placing a leech on a person and allowing it to consume blood. Leech saliva contains hirudin, a chemical that prevents blood from clotting. Leeches can be used during reconstructive surgery as an aid in increasing blood flow to the affected area. They have also been used to treat osteoarthritis (Cooper and Mologne, 2017).
Leeches and Turtles: A Match Made in the Wetlands
Two species of leeches commonly parasitize turtles in Canada, the smooth turtle leech and ornate turtle leech. However, Helobdella modesta was discovered on Canadian turtles in a 2009 study (Davy et all, 2009). Leeches tend to attach themselves to a location on a turtle where they can’t be scratched or bitten off, like at the base of a turtle’s tail or behind a limb.
Leeches don’t just feed off turtles, they also use turtles as a method of transportation (Davy et al, 2009)! While leeches are keen swimmers, a leech can travel farther and faster by attaching itself to a turtle than by swimming alone. This is an example of phoresy, or when one animal uses another animal as a way of travelling. According to a study conducted in Brazil, leeches may have a phortetic relationship with toads (Maia-Carneiro et al, 2012). The marine turtle leech, Ozobranchus margoi, even lays eggs on their sea turtle hosts (Göpper, 2018).
A leech attached to a turtle can also be a tasty meal! Birds such as grackles have been observed eating leeches from map turtles (Vogt, 1979). Painted turtles eat leeches and algae off of snapping turtles, whereby the painted turtles benefit by getting an easy meal, and snapping turtles get a free cleaning (Krawchuk, 1997). It’s a win-win situation!
Animals such as birds and squirrels may use ants to remove parasites from themselves. This is called anting. Turtles have been observed to use anting to remove leeches as well! In one study, snapping turtles that nested in anthills were typically found without leeches. One turtle had even buried herself under an anthill, and was completely free of leeches (Burke et al, 1993)!
Wood turtles may also engage in anting. In one study, a wood turtle was found with ants and leeches at the base of her tail. While no ants were observed eating the leeches, it was suspected that the turtle was displaying anting behaviour (Hughes, 2016).
Whether as predator, prey, or an indicator of water quality, leeches play an important role. They might be considered creepy, but wetlands wouldn’t be the same without them!
Sources Cited
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