Range: Cosmopolitan Habitat: Lakes, ponds, streams, and moist soil Size: Animal blood, insects, and detritus Diet: About 8 inches - 1.5 feet (20.32-45.72cm) long Threats: Reptiles, amphibians, birds, and more Life span: Varies by species

Transcript:

Today on Animal Fact Files, we’re discussing leeches. Stay up to date on new episodes by subscribing! Vinny Sch suggested today’s interesting animals. Many people are grossed out by leeches. It makes sense considering some these literal bloodsucking creatures do consider humans a source of food, but they’ve also been beneficial to humans throughout history.

Leeches are found on every continent except Antarctica (but seriously are you even surprised by that?). Some live on land and in marine environments, but most of them are found in freshwater habitats. Leeches live in lakes, ponds, streams, and moist soil, with most of them being found along the edges of waterways. There are leeches that focus mostly on mammals, but there are also species that primarily attach to reptiles, fish, and even birds, so not all leeches are out for our blood.

Leeches move kind of like inchworms, and they look like earthworms; this is because both earthworms and leeches are segmented worms. Earthworms continuously add segments to their bodies as they grow, but leeches always have the same amount. In fact, baby leeches emerge from their cocoons looking like smaller versions of their parents meaning they don’t have a larval stage.

Like earthworms, leeches have both male and female reproductive organs, however, they’re not able to self-reproduce and thus rely on fertilization from another member of their species to pass on their genes. A leech will produce a cocoon, and the amount of eggs inside can depend on the species. As of this recording there are thought to be around 650 different species of leeches. Some leeches lay a cocoon on rocks along a shoreline leaving their children to fend for themselves; others, however, may carry the cocoon with them and then the young once they have emerged.

For many young leeches, their jaws aren’t strong enough to penetrate the skin of their adult-form hosts, so they have to settle on smaller animals such as frogs. Also, some species of leeches need to feed only once every few months, while others feed at a faster rate. And some leeches even eat meals like insects or even detritus instead of sucking blood. There’s a lot of variety between all the leech species! Their lifespans can also vary, though it’s thought that many will perish after reproducing.

Some leech species can get huge, like the giant Amazon leech who can grow to a foot and a half (45.72cm) in length; others are smaller, only reaching about eight inches (20.32cm) in length. I say “only” but that’s still pretty big when considering it might attach to your body and suck your blood.

Leeches that feed this way usually don’t consume much blood, as they’ll fall off a host once engorged, however, the way in which they obtain their meal causes more blood loss than what the leech itself can eat. When a leech bites, its anesthetic-like saliva makes the bite almost imperceptible. The leech will also release an anticoagulant that prevents the host’s blood from clotting. This allows the blood to flow easily into the leech, but also once the leech has detached. It’s this property of the leech’s bite that has caused humans to use them medicinally for millennia. Even today they can be used to help with the recovery process of reattachment of severed limbs, though many patients have an adverse reaction to this method. Would you let a leech attach to you if it meant saving a severed finger or ear?

For more facts on leeches, check out the links in the description. Give a thumbs up for bloodsucking creatures, and thank you for watching Animal Fact Files.