Living Nightmare: World’s Largest Leech Grows Up To 18 Inches Long


The Amazonian Giant Leech, otherwise known as Haementeria ghilianii, is the biggest leech in the world by an impressive margin — it can grow up to a whopping 18 inches (46 cm) long. Leeches live in wet, humid places all over the world, and while the majority of them are no bigger than a normal person’s index finger, some of them can grow to massive sizes.

The Haementeria ghilianii species in particular is so large it’ll probably give you nightmares. This elusive leech only resides in some parts of Brazil and in French Guyana, so unless you live in or are visiting one of those countries, you’ll probably never see one in the flesh. Still, just looking at photographs of this slimy beast is enough to give you goosebumps. Although the majority of these critters are 30-25 centimeters long, the unusually big ones can reach up to 46 centimeters.

Italian naturalist Vittore Ghilliani discovered the Amazonian Giant Leech in 1849, and ever since then, it’s been regarded as a near-mythical creature due to its abnormal size and appearance. While there isn’t recorded scientific proof that backs this up, there are plenty of legends and folklore about these oversized leeches drinking all the blood out of an adult human in just hours. 

These claims date back to 1899 and assert that just a few leeches could kill cattle and horses by draining their blood. Although not much information about this exists on the internet, it’s thought that the Haementeria ghilianii can suck blood at an alarming rate of 04 to 15 milliliters per minute.

Other leeches with jaws use their teeth to puncture the skin of their host, but the Amazonian Giant Leech extends a terrifyingly sharp, dagger-like appendage called a proboscis out of its mouth to pierce its host’s skin. Despite the proboscis being ten centimeters long, the host isn’t likely to feel it inserted. That’s because this sneaky leech secretes a cocktail of chemicals that numbs the area it pierces. The saliva in the Giant Leech is filled with a powerful anticoagulant that ensures blood keeps flowing long after the leech has detached itself from its victim.

Haementeria ghilianii can remain alive for many months at a time without eating, so it can patiently wait until the next unfortunate host comes its way. When it’s fasting and hasn’t eaten in months, it can appear significantly smaller, but as soon as it gorges on as much blood as it can handle, its weight can increase by 3 to 6 times per feeding. 

This rare Amazonian leech is more solidly built than you’d think. Mark Siddall of the American Museum of Natural History claims that, due to its strong longitudinal muscles, even if you stepped on this animal with a boot, you couldn’t kill it. So if you do end up running into one of these monstrosities in the wild, you’d better take some extra precautions to make sure it’s actually dead or, at the very least, far, far away from you.