Ryukyu Land Leech (Taipei)

English Name: Ryukyu Land Leech, Ryukyu Mountain Leech
Scientific Name: Haemadipsa rjukjuana
Chinese Name: 琉球山蛭 (liu2 qiu2 shan1 zhi4)  
Chinese Meaning: "Ryukyu Mountain Leech"

Ryukyu Land Leech (Haemadipsa rjukjuana)

Date: October 24, 2011
Location: Maokong Yuanshan, Wenshan Districty, Taipei City 
Coordinates: 24° 58' 8" N, 121° 36' 04" E

Taiwan is a paradise for nature walks, but hikers sometimes have to deal with the nuisances of the tropical forest - mud, mosquitos, and leeches. Contrary to popular belief, not all leeches are bloodsuckers. Some of these earthworm-relatives in fact prefer to hunt small prey that they can swallow whole, such as worms or small snails. Of those that do feed on blood, most in fact do not attack humans, instead preferring to attach to water snails, fish, and frogs. However, Myth #2 about leeches is less comforting: in reality, not all leeches live in the water. Some species, such as the one pictured here from the land leech family Haemadipsidae, are fully adapted to life on land, waiting on moist plants for a passer-by to provide their next meal.

Foraging Ryukyu Land Leech (Haemadipsa rjukjuana) with body
extended (left) and contracted (right)

This leech species is named after the Japanese Ryukyu Islands just northeast of Taiwan, and is also found in much of Southeast Asia. It's an active hunter, spending its time near the forest floor, waiting for large mammals like humans or dogs to come near. It has a disconcerting habit of stretching its body up off the ground and waving its head around in the air, searching for a meal using its complex sensory system, which can detect changes in vibration, airflow, brightness, and temperature. Once it zeroes in on a target, it crawls inchworm-style along the ground or vegetation, then up onto the body of the new host, looking for areas of soft skin to bite into. Although it has no problem moving on land, it does require a moist environment, and it can usually be avoided by making sure not to brush your feet up against wet plants.

Ryukyu Land Leech (Haemadipsa rjukjuana) feeding on human blood.

As a kid, I always thought that leeches drank blood using big suckers on their heads. However, I recently learned that the large sucker on the fat end of the leech is actually its tail (seen on the right in the photo above), which it uses to hang on while it feeds with a much smaller sucker on the small end, which is actually its head (seen on the left). The dried blood on the far right of the photo is from a separate bite, inflicted by the leech from the first photo. You don't feel a thing when the leech bites, but the wound continues bleeding for awhile after it detaches, because of a chemical called hirudin that the creature injects into your blood. The next day, the area swells up into a bump like a mosquito bite, and keeps itching for a week or more. For information on how to remove a leech from your body and treat the bite, see this Wikipedia article.

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Note: Special thanks for this entry go to a wonderful book called Leech Fauna of Taiwan by Yi-Te Lai & Jiun-Hong Chen. Although it's written for academic audiences, it's a great guide for dedicated amateur naturalists as well. If you're on a tight budget or can't get to a library, most of the information from the book can also be found online at the Biota Taiwanica website (leeches are farther down the list, after all the earthworms).