Leeches are probably the most well known denizens of tropical/subtropical rainforests worldwide, and no description of a rainforest would be complete without mentioning them. These bloodsuckers are segmented worms (Annelida) and related to earthworms. They are present all over the world but especially ubiquitous in the tropical zone.
You can find them in almost every patch of moist jungle, with few exceptions, ranging from the lowlands, all the way up to mountain peaks. The only places where they don’t exist are areas with no wildlife (no blood supply) to feed from, or very cold areas like the peaks of the highest mountains. There are also aquatic leeches that live in marine and freshwater environments, so don’t think the water’s safe! In fact, I find that jungle riverbanks and some river islands have a high concentration of them.
Types of leeches
Leeches are broadly divided into jawed and non jawed groups. The jawed leeches are the ones humans are most familiar with, and this includes a wide range of temperate and tropical leeches, such as the famous European leech (Hirudo medicinalis) which is used for blood-letting purposes in hospitals, and of course, the Malaysian leeches (of which there are many species), but collectively, they are called “pacat” or “lintah” in Malay. Pacat refers to the common small leeches always encountered in the rainforest, while lintah is a larger, more specialized leech that is found in freshwater swamps (often referred to as buffalo leeches).
Generally speaking, the jawed land leeches belonging to the Hirudidae family have 32 internal segments (which do not correspond with their much more numerous external segments), 3 sharp teeth, and strong sucking disks on both ends of their body. It is said that they also have 32 brains in each of their internal segments! Leeches are very sensitive to heat, vibration, and possibly smell.
One of the commonest land leeches in South East Asian rainforests, is Haemadipsa zeylanica, but note that the same species also occurs in Japan, where it is called the Yamabiru mountain leech. Possibly, those in Malaysia are a subspecies of H. zeylanica since they look so similar. It is brown in color with two black bands/stripes running down its sides and a single dorsal line running down its top, and normally about 3-5 cm long when outstretched.
Haemadipsa zeylanica is so widespread that researchers recognize a multitude of subspecies originating from it. In Malaysia alone, I believe there are many types of leeches, but due to lack of research, hardly anything is known about them. There is a smaller species or subspecies of leech similar to H. zeylanica that looks a darker brown (actually almost black in color), and is normally 1-3 cm long, which is commonly encountered, coming out in hordes after rain as little black worms waving in the air on the forest floor. This leech is probably the one they call “pacat”. It’s the stealthiest of leeches due to its size and lack of sensation when it bites. If no protection measures are taken, it’s common to pull off your shoes after a short hike and find around 10 or more of them inside, sucking on your feet!
Another common land leech in South East Asia is Haemadipsa picta, or the Tiger Leech. It is also called the Painted Leech, due to its bright yellow/orange coloration on the bottom, greenish brown on the top, and a yellow stripe along both sides. The Tiger Leech climbs low vegetation to ambush its prey when they brush pass the vegetation, but its bite is often accompanied by a stinging sensation, so they are not as successful in getting to feed on humans as the common brown leech. If you are trekking in the jungle, and you suddenly feel a sharp stinging sensation possibly followed by something cold on your skin, chances are, it’s a Tiger Leech that has fastened onto you.
As mentioned earlier, there is also the lintah or buffalo leech (Hirudinaria manillensis), which is a large leech (10+ cm) found in swamps and rivers and mainly feeds off large prey like cattle. It is also called the Asian medicinal leech due to its suitability as a natural bloodletting “tool” and there are some farms in Malaysia that farm this leech for its “oil” to be used as a male enhancement “Jamu” stimulant! NB: Jamu is traditional South East Asian medicine, similar to Ayurveda or TCM but with the cosmetic aspect. The belief is that the leech’s flexibility, “strength”, and ability to lengthen itself would be “transferred” to the male organ if the man regularly rubs the leech oil onto it.
There is another large leech, the Chain Striped Leech (Phytobdella catenifera), that dwells around streams and waterfalls, but fortunately, this species only preys on cold blooded reptiles and amphibians and therefore, rarely encountered. It has a rather striking pattern of cream-colored spots running along its dorsal and sides, as well as smaller specks all over its body.
How do leeches feed?
When leeches bite, they inject an anticoagulant called hirudin. Hirudin is injected by the leech upon puncturing its victim’s skin with its sharp jaws, and it acts to prevent the blood from clotting, thus enabling a continuous flow of blood for the leech to suck on. Hirudin is such a powerful anti-clotting agent that wounds often continue bleeding for up to several hours (it’s a real drag) after the leech has dropped off. This is especially so for large/adult sized leeches, since they inject more hirudin, compared to the smaller ones.
One nice meal of blood can sustain a leech for months, because after feeding, they hibernate and digest their meal really slow. If you squeeze an apparently starving leech hard, a little residual blood can sometimes still ooze out of it!
What to do if you’ve been bitten?
Yikes, leeches are gross I know, and maybe the large ones are a little scary (even for me). But they do not transmit diseases when they bite. The bleeding is very inconvenient though, and how long it continues bleeding, depends on the amount of hirudin injected. If the leech is removed before or soon after it has begun to bite, there won’t be enough hirudin injected to cause any damage. But if the leech is removed after it is already bloated or near to being satiated, the bleeding is usually troublesome and continues for some time.
If you can, place a thick piece of cotton wool/tissue on the body part that has been bitten, and then position that area so that it is above the level of your heart. This reduces the blood pressure to the area, and helps the blood to coagulate. For example, if you’ve been bitten on your foot, lie down and place your foot at a higher level than your heart for around 20 minutes. This procedure only works if the wound has already bled most of the residual hirudin out. If the hirudin is still present in the wound area, chances are, the bleeding will start up again if the wound is disturbed in the slightest way later on, for example by washing or bathing it.
Leeches can be removed simply by scraping or yanking them off. There is no pain involved, and they do not leave behind any mouth parts on your skin (contrary to popular belief). If you can make them drop off, this is even better of course. Here is a partial list of anti-leech substances:
- Dried tobacco
- Salt (soak socks/clothing in saltwater)
- Citronella extract in concentrated form (mosquitoes hate them too)
- Most insecticide (especially those containing DEET) as long as it is not too mild
- Neem, eucalyptus, or most strong medicinal oils
- Heat from a lighter
There is some debate as to whether applying anti leech substances on the leeches will cause them to vomit the blood out into your wound and therefore, is detrimental or not (although the risk of contracting a blood borne disease is microscopic). I personally just flick, scrape, or yank them off – all the time.
As far as I am concerned, leeches are my only pet peeve whenever I go jungle trekking. Here, prevention is always better than cure. The best way to stop leeches is to not let them bite you in the first place. And the best leech prevention method is by wearing leech socks. Better still, leech socks soaked in salt+oil+tobacco mixture. Oil keeps the substances from being easily washed off in streams or rivers.
However, I have noticed certain aboriginal people who hardly ever get bitten by leeches, and so far I have never found out their secret. Perhaps one day, I will. It might be that they consume certain jungle plants which make their blood or scent less appetizing for leeches. It might be that the leeches are so used to the aborigines that they can’t be bothered. Heck, it just might be something else….