Saturday, 27 September 2014

Monster leech sucks down giant worm like spaghetti #WondersofTheMonsoon BBC2

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'Wonders of the Monsoon' starts on BBC2 5/10/14
Please Note: The leech that we filmed was 50 cms long, half a metre.
This story was first published by the Telegraph 26/Sept/2014

On Mount Kinabalu in Borneo lives the legendary Giant Red Leech - one of the biggest leeches in the world. Fortunately they don’t have a taste for blood, instead they hunt giant blue worms and suck them down like spaghetti, revealed for the very first time in our new BBC 2 series ‘Wonders of the Monsoon’.

Cameraman Richard Kirby and I travelled to Mount Kinabalu in Borneo in the hope of catching a glimpse - what we managed to film was simply gobsmacking. We joined ecologist Alim Biun who was keen to study the elusive animal.

The giant leeches are so mysterious that they don’t even have a full scientific name. "I am convinced that the Kinabalu Giant Leech is obviously an undescribed species of the genus Gastrostomobdella." said Leech scientist Dr Takafumi Nakano of Kyoto University.

“Very little is known about them, we don’t know how they hunt, or even how big they grow, because no one has researched them” said Alim.

The individual we filmed was 50cms long - 1/2 a metre and the worm was even longer

Finding the species on mount Kinabalu, the biggest mountain in Borneo, was a huge challenge. But if you want to film a predator the best thing to do is to find its prey, but it took us several weeks of searching before an extremely heavy rainstorm eventually brought worms out in huge numbers. Sure enough the red leeches were not far behind. Alim and his team quickly collected specimens and moved them to an open area, where the scientists could see what was going on.

By working with Alim we were able to sufficiently light the area of forest to record the predation as it unfolded It was exciting and fascinating, as he was making his new scientific discovery, we were documenting the behaviour for the very first time.

Our extraordinary new footage reveals how the giant leech (the leech in the video is 50cms long) is able to quickly detect a worms trail, and like a sniffer dog follow it and latch on to its prey. “There are many sense organs on the bottom surface of their oral sucker and they can probably sense the chemicals and the shed cuticles of the worms.” said Dr Takafumi Nakano.

Giant blue worms, almost 70 cms long. After a heavy rainstorm they emerge in large numbers to mate... and where you find the prey, the predator isn't far behind.

The leech looks for an end to grab

Once it had latched on, the leech creepily moved its quivering lips up and down the worms iridescent blue body. It was either searching for an end to grab, or was working out whether it was too big to eat, non-the-less, when it found an end it started to suck. It was incredible. The worm tried to pull away but slowly the leeches lips inched forward until with a slurp, the worm was gone.

The worm tries to escape but the leeches lips slowly inch forward

A long way to go but the leech continues to devour the worm

Dr Nakano who has studied a much smaller relative of the Giant Kinabalu Leech said “When they eat too large or too many earthworms, they often throw up portions or whole body of the worms.” This is behaviour similar to that seen in large snakes, like the reticulated python. With poor vision the snake has no accurate way to tell how big the prey is and so they keep on swallowing until its too much - with no way to bite off a chunk they have no option but to regurgitate the prey. This is the same behaviour we saw a few times with the giant leech allowing the worm to make a quick exit.

The whole process of swallowing the worm lasted about 15 minutes and then the leech disappeared under leaf litter, coiling up to digest its meal. Dr Nakano estimates that it would take about a month for the leech to digest the worm. The result is that we can confirm the predatory behaviour of a rarely-seen and unidentified species for the first time.

When the story was reported in ifls Leech expert Dr. Mark Siddall of the American Museum of Natural History said, “I think the BBC footage is terrific and I am eagerly looking forward to the Monsoon series. I have often wanted to see this in action for myself; the only existing video (from a related species in Japan) suggests they eat earthworms sideways, which never made sense to me. Williams and his team have made an important contribution to my field. It will be interesting to see if this is indeed a new species, or if we leech taxonomists got it wrong in the past..." 

Mount Kinabalu, home of the Giant Red Leech, Borneo

The giant red leech features in episode 4 of 'Wonders of the Monsoon', to find out more about this remarkable species and how we worked with the scientists to find it, watch the episode and the behind the scenes section at the end.


  1. Thanks Paul. I'm glad you wrote this - I was getting confused by the press coverage. 1/2 metre sure is impressive enough!!

    1. Just spotted this. thought 30cm was big enuf. lol.

  2. Awesome and yet terrifying!

  3. Simply mesmerising! Can't wait for this series Sky+ set to record ;-)