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Giant Predatory Terrestrial Leech

Diestecostoma sp.


I came across this leech at night in the middle of the street. I thought at first it was a small snake since it was covered in dirt and sand and was several cm long. However, a photo showed the segmentation of an Annelid (picture 3). I picked it up and saw that it had a sucker on the caudal end. I took it home and washed it off and put it in a terrarium with a small bowl of water. It started off in the water, but preferred to be out of the water. It has both a caudal sucker and can turn the anterior pointed end into a sucker as well. It moves by fastening the posterior sucker to the substrate, searching and stretching forward with the anterior end. It then forms the anterior sucker and releases the caudal sucker to catch up to the front. This one reached a maximum length of 22 cm! When reduced, it is between 6 and 8 cm in length and of course much fatter (last picture). Leeches are Annelids and thus are segmented throughout the length of the body, allowing such enormous size incrementation. See this video of it's movement ( These leeches are predators and search out and feed on earthworms and probably larvae in the soil and slugs as well. They attach with the anterior end, begin to envelope their prey and eventually suck it in and swallow the entire thing whole. The 4th picture shows the anterior sucker attached to glass. They do not have teeth and there are some papillae on one side. The suction is quite strong and is formed with mucous. The first two pictures show the leech attached to a piece of paper with both suckers actively attached. It is difficult to break the seal without hurting them! I have to admit I was quite shocked that such a monstrous leech even existed here. It was both fascinating and creepy. I let it go again close to the wetlands in a damp place with lots of vegetation. This is a very uncommon creature to see and I hadn't even known it existed. Family Xerobdellidae (Hirudinea, Annelida). See this BBC article of how a giant predatory leech from Borneo eats an earthworm: ( See Leech Expert Mark Siddall's TED Talk on Leeches:


While I found it in the street, it definitely wasn't happy and probably washed down from wherever it had been during the rains the day before. I am glad it wasn't run over by a car. Semi-rural residential area, San Cristobal de Las Casas, Chiapas, Mexico.


Four species of Terrestrial Predatory Leeches are a possibility for this one: Diestecostoma magna, Diestecostoma mexicana, Diestecostoma octannulata and Diestecostoma trujillensis. There is very little information and almost no pictures of these animals. The identification is based on minute morphological details that would have required fixing the leech in alcohol. I don't know if any of these have been reported from the Chiapan highlands, although D. octannulata has been reported from the lowland border between Chiapas and Guatemala. I sent these pictures to Dr. Mark Siddall, a leech expert at the National Museum of Natural History and he wrote back: "My goodness! That is a very big one! There are several kinds of terrestrial or semi terrestrial leeches in Mexico and further south in Central America. Diestecostoma, as you inferred is one, but also Cylicobdella. Judging by the Y shaped mouth, I would say it is a very large Diestecostoma".

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LaurenZarate a year ago

Update on this leech: Dr. Mark Siddall of the National Museum of Natural History and a leech expert confirms that this is probably a very large Diestecostoma based on the Y-shaped structure inside the mouth sucker (4th picture).

LaurenZarate a year ago

Thank you Ashley for the nomination. I don't think even 95% of the world know that a leech like this exists. I sure didn't. Amazing creature.
Thank you Maria and Hema :)

Maria dB
Maria dB a year ago

This is really interesting - wonderful spotting!

AshleyT a year ago

Your spotting has been nominated for the Spotting of the Week. The winner will be chosen by the Project Noah Rangers based on a combination of factors including: uniqueness of the shot, status of the organism (for example, rare or endangered), quality of the information provided in the habitat and description sections. There is a subjective element, of course; the spotting with the highest number of Ranger votes is chosen. Congratulations on being nominated!

Hema a year ago


Hema a year ago

are you planning to return it to it's habitat? Be careful
that it does not larch on to you!!

LaurenZarate a year ago

Thank you Mark, it really is amazing and creepy.

Mark Ridgway
Mark Ridgway a year ago

Oh my goodness.. fantastic spotting Lauren.

LaurenZarate a year ago

Sorry, BBC video. I still have to put up my own.

LaurenZarate a year ago

Thank you Trggsturner. Yes! A monster! It is shocking to see it reach 22 cm. And the suckers feel horrible. Be sure to see that NatGeo video!

triggsturner a year ago

Wow, this guy is a monster! Biggest leech I ever saw was a giant leech in Sumatra but this one of yours look even bigger! Nice spotting Lauren

Spotted by

Chiapas, Mexico

Spotted on Oct 6, 2018
Submitted on Oct 10, 2018

Spotted for Mission

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