Animal Species:Leeches
Leeches are annelids or segmented worms, and although closely related to the earthworms, are anatomically and behaviourally more specialised.
Identification
Leeches are segmented worms in the Subclass Hirudinea that are usually ectoparasitic. They belong to the Class Clitellata (along with earthworms, Subclass Oligochaeta) because of the presence of a clitellum, which is a swelling towards the head of the animal, where the gonads are located. However, unlike the oligochaetes, leeches do not show the clitellum all year. Instead, it only becomes visible during the breeding season.
Leeches are bilaterally symmetrical, with thick muscular bodies. Usually they are dorso-ventrally (front to back) flattened and segmented, though the segments are not often seen. Some leeches are long and worm-like, others pear-shaped and broad. Most can vary considerably in shape both between the elongated and contracted state and between the starved and full condition.
The body tapers towards the head and has a small oral sucker surrounding the mouth and a larger caudal (tail) sucker at the rear end, except the marine fish parasites, Pisciolidae, which have a larger oral sucker. The anus is on the dorsal surface (top) just in front of the rear sucker.
Euhirudinea ('true' leeches) have 32 internal segments when mature and Acanthobdellida (a small group of fish leeches) have 29, but counting is difficult because four to six segments are included in an front sucker and seven in a rear sucker, while the remaining segments are secondarily annulated (ringed) to give two to five apparent segments per internal septum (internal membrane).
Unlike other annelids, leeches do not have parapodia ('feet') or chaetae (bristles) (except for Acanthobdellida).
Leeches usually have three jaws and make a Y-shaped incision. The Australian land leech has only two jaws and makes a V-shaped incision.
Size range
7 mm long to 300 mm when extended
Distribution
There are around 500 species of leeches world wide. These are divided into two major infraclasses
- Euhirudinea: the 'true' leeches – marine, freshwater and terrestrial – which have suckers at both ends and lack chaetae (bristles)
- Acanthobdellida: a small northern hemisphere infraclass ectoparasitic on salmoniid fish, which lack an anterior sucker and retain chaetae.
The Euhirudinea is further divided into two orders:
- Rhynchobdellida: jawless marine and freshwater leeches with a protrusible proboscis and true vascular system
- Arynchobdellida: jawed and jawless freshwater and terrestrial leeches with a non-protrusible muscular pharynx and a haemo-coelomic system.
Leeches can be found almost anywhere in Australia where there are suitable damp areas and watercourses although they are absent from the permanently arid areas. There are even marine leeches, but these feed on the blood of fishes (including the Electric Ray with its fearsome electric shocking abilities) and other marine life – not humans.
Habitat
Most leeches are freshwater animals, but many terrestrial and marine species occur.
Land leeches are common on the ground or in low foliage in wet rain forests. In drier forests they may be found on the ground in seepage moistened places. Most do not enter water and cannot swim, but can survive periods of immersion.
In dry weather, some species burrow in the soil where they can survive for many months even in a total lack of environmental water. In these conditions the body is contracted dry and rigid, the suckers not distinguishable, and the skin completely dry. Within ten minutes of sprinkling with a few drops of water, these leeches emerge, fully active.
Freshwater leeches prefer to live in still or slowly flowing waters, but specimens have been collected from fast flowing streams.
Some species are considered amphibious as they have been observed in both terrestrial and aquatic habitats.
Feeding and Diet
Most leeches are sanguivorous, that is they feed as blood sucking parasites on preferred hosts. If the preferred food is not available most leeches will feed on other classes of host. Some feed on the blood of humans and other mammals, while others parasitise fish, frogs, turtles or birds. Some leeches will even take a meal from other sanguivorous leeches which may die after the attack.
Sanguivorous leeches can ingest several times their own weight in blood at one meal. After feeding the leech retires to a dark spot to digest its meal. Digestion is slow and this enables the leech to survive during very long fasting periods (up to several months).
Leeches are grouped according to the different ways they feed:
- One group (the jawed leeches or Gnatbobdellida) have jaws armed with teeth with which they bite the host. The blood is prevented from clotting by production of a non-enzymatic secretion called hirudin. The land leech commonly encountered by bushwalkers is included in this group.
- A second group (the jawless leeches or Rhyncobdellida) insert a needle-like protrusion called a proboscis into the body of the host and secrete an enzyme, hemetin which dissolves clots once they have formed. Leeches which live on body fluids of worms and small freshwater snails possess such an apparatus.
- A third group, (the worm leeches or Pharyngobdellida) have no jaws or teeth and swallow the prey whole. Its food consists of small invertebrates.
Foraging
A hungry leech is very responsive to light and mechanical stimuli. It tends to change position frequently, and explore by head movement and body waving. It also assumes an alert posture, extending to full length and remaining motionless. This is thought to maximise the function of the sensory structures in the skin.
In response to disturbances by an approaching host, the leech will begin 'inchworm crawling', continuing in a trial and error way until the anterior sucker touches the host and attaches. Aquatic leeches are more likely to display this 'pursuit' behaviour, while common land leeches often accidentally attach to a host.
Other behaviours and adaptations
Respiration
Respiration takes place through the body wall, and a slow undulating movement observed in some leeches is said to assist gaseous exchange. Aquatic leeches tend to move to the surface when they find themselves in water of low oxygen content. As a fall in atmospheric pressure results in a small decrease in dissolved oxygen concentrations, rising leeches in a jar of water provided nineteenth century weather forecasters with a simple way of predicting bad weather.
Sensory organs
Sensory organs on the head and body surface enable a leech to detect changes in light intensity, temperature, and vibration. Chemical receptors on the head provide a sense of smell and there may be one or more pairs of eyes. The number of eyes and their arrangement can be of some use in Identification, however to properly identify a leech, dissection is required.
Colour changes
The Rhyncobdellids are capable of dramatic colour changes but this is apparently not an attempt at camouflage, and the significance of this behaviour is unknown.
Locomotion
Leeches move by either an undulating swimming motion (eel-like) or by an 'inch-worm' like crawling motion using the anterior and posterior suckers. The posterior sucker is attached to a substrate and the leech stretches out and attaches to the substrate with the anterior sucker, the posterior sucker is then detached and pulled up to the anterior sucker.
Mating and reproduction
As hermaphrodites, leeches have both male and female sex organs. Like the earthworms they also have a clitellum, a region of thickened skin which is only obvious during the reproductive period. Mating involves the intertwining of bodies where each deposits sperm in the others' clitellar area. Rhyncobdellids have no penis but produce sharp packages of sperm which are forced through the body wall.
The sperm then make their way to the ovaries where fertilisation takes place. The clitellum secretes a tough gelatinous cocoon which contains nutrients, and it is in this that the eggs are deposited.
The leech shrugs itself free of the cocoon, sealing it as it passes over the head.
The cocoon is either buried or attached to a rock, log or leaf and dries to a foamy crust. After several weeks or months, the young emerge as miniature adults. Studies show that the cocoons are capable of surviving the digestive system of a duck.
Leeches die after one or two bouts of reproduction.
Predators, Parasites and Diseases
Fish, birds and other invertebrates are the main predators on leeches.
Economic/social impacts
Medicinal use of leeches
For over 2000 years, leeches were needlessly applied for many ailments as an adjunct to blood letting. Their use in Europe peaked between 1830 and 1850, but subsequent shortages led to a decline in their use. Today there is a real clinical application in that they are of great value to plastic surgeons when venous congestion of skin and muscle flaps is a problem.
Leeches are treated in the same way as blood products and are reused only on the same patient.
Medical use of leeches also includes treatment of black eyes, and hirudin is used in the treatment of inflammation of the middle ear. Hirudin is also being developed for experimental use as a systemic anticoagulant, and may prove useful in invitro blood sampling.
Leeches in Sydney suburbs
The Sydney suburban sprawl is resulting in houses extending into areas such as wet valleys that leeches normally prefer. It is therefore less distance for these leeches to travel in wet weather before they end up in backyards and can get a meal from domestic animals or humans living there. Similarly the domestic animals and humans themselves unwittingly bring many leeches home with them from bush walks, holidays, and other travels. If these leeches are adult they will invariably find a suitable damp spot in the garden to lay their eggs and suddenly you have a colony of leeches in your backyard.
Management
Leech repellents
The most common enquiry regarding leeches concerns repellents. It is unknown whether a specific preparation is commercially available but there is a plethora of tried and tested, but unproven leech-protection ideas. These include a lather of bath soap smeared on exposed parts and left to dry, applications of eucalyptus oil, tropical strength insect repellent, lemon juice and impenetrable barriers of socks and pantyhose.
Danger to humans and first aid
The presence of hirudin in the wound following a leech bite may cause oozing to continue for several hours. Although inconvenient, blood loss is not significant.
Gut bacteria can cause wound infection. In the post-operative use of leeches this is closely monitored and dealt with by use of the appropriate antibiotic.
There may also be a delayed irritation and itching after a bite. There appears to be no support for the theory that mouthparts left behind after forced removal of the leech causes this reaction.
Can leeches transmit disease?
There is no evidence to suggest that they do. The presence of trypanosomes, (malarial parasites), in the gut of jawless leeches has been noted, but jawed leeches do not appear to be hosts.
Allergy to leech bite has been reported. Medical opinion should be sought, depending on the severity of the reaction.
Classification
- Subclass:
- Hirudinea
- Class:
- Clitellata
- Phylum:
- Annelida
- Kingdom:
- Animalia
References
Last Updated:
Tags leeches, worms, segmented, segmented worms, invertebrates, identification,
34 comments
Helo Katrina,
I have not heard of symptoms such as these resulting from a leech bite but certainly the wound can become infected with bacteria so it could be the result of a secondary infection. I'd seek medical help if the symptoms persist.
Martyn Robinson
Hello Jagga,
Typical clues of a leech bite are profuse bleeding for a long time, and a large bloody scab in proportion to the size of the bite. The leech bite itself is 'V' or 'Y' shaped. They often itch quite a bit over the next few days after the bite, which usually starts the bleeding all over again if you scratch them.
I hope this helps.
Martyn Robinson
Hello Gerontius,
Sorry for the late reply but I've been away. There is a known worm-eating leech recorded called Bassianobdella bundabergii which sounds very much like yours. If you look up 'Queensland's earthworm eating leech' on the internet you should be able to find out more about it.
Martyn Robinson
Hello Julie-Anne,
No - what has happened here is your original leech bite proved too tempting to some tiny baby aquatic leeches that were still present in the swimming area. Leeches produce a sort of 'egg co[Removed]' which, in the land leeches, is hidden in the leaf litter, and in aquatic leeches is attached to rocks or water plants. The water leeches followed the trail of leaking blood in the water onto your leg
Martyn Robinson
Hello Denise,
Please send an image of your 'leeches' to us as I suspect they may be something else and probably harmless - although they could indicate your water tank filter needs fixing!
Martyn Robinson
Hello Rozalia,
Yes salt would work but won't be good for your house. Also the animals you describe certainly don't sound like leeches. They are almost certainly Blue Land Planarians (Caenoplana coerulea) a harmless predatory species which actually feeds on some garden pests like the Portuguese Millipede. I'd leave them be if I were you. More detail on the Blue Land Planarian is below if you want to see if they match:-
http://en.wikipedia.org/wiki/Caenoplana_coerulea
Martyn Robinson
Hello Wendy,
Land leeches are common in many areas of NSW where conditions are damp or humid. They feed on warm-blooded prey including birds and mammals like Ground Thrush, Brush Turkey, bandicoots, possums, kangaroos and the like. Some other land leeches feed on cold blooded prey like frogs but these rarely bite humans. The leeches seek out areas on the host where they are difficyult to remove - otherwise they would be detected early on and wouldn't complete their feeding. They also apply an anaesthetic to the bite site so you don't feel it and an anticoagulant so the blood keeps flowing.
I hope this helps
Martyn Robinson
Hello Abhay,
The care and diet of your leeches will depend on what species of leech they are. Obviously land leeches will need to live in damp conditions on land while aquatic leeches will need pond or creek water to live in. Also some leeches feed only on the blood of of a few types of animals e.g. snail leeches, fish leeches, turtle leeches, Others are broader in their diet and will feed on any warm blooded animal or any cold blooded animal. Still others again are predators on smaller animals and swallow them whole - including some that feed only on other leeches.
If you send in a photo to us we may be able to help you identify your leeches but perhaps your best chance for an identification is to send it to the biggest natural history museum in your local area as they will have a better idea of what is living in your area.
Sincerely
Martyn Robinson
Hello Mark,
I think the best idea is for you to contact me directly at the Australian Museum (either by ringing up or by using the staff profile contact via e'mail) as there will be quite a bit of detail to discuss - maybe a bit too long for the space here. In the meantime if you can get to Somersby Store (car or bus), and either travel north or south along the Great North Walk (it is well signposted but you can always ask at the store for directions if you are not sure) then you should soon come into contact with leeches - particularly in the current wet weather.
I'll hear form you soon - in the meantime good luck with the leech hunting.
Sincerely
Martyn
Hello Mark,
Perhaps the best advice I can give you if you live in Sydney is to travel the Great North Walk sections from Ourimbah to Newcastle. Any of the track sections through the rainforest - particularly after rain - will be FULL of leeches and just walking along the track will provide you with many just by removing them from your legs and feet. Other good places to visit are some of the rainforest walks in the Blue mountains and Royal National Park - but NONE has ever matched the Great north Walk in my opinion.
Happy hunting!
Sincerely
Martyn Robinson
Hello Glenn,
Unfortunately I don't think I can tell you which brand as - like the ABC - we're not supposed to do that sort of thing, but there aren't that many sunblock creams out there with insect repellent added as well, so it shouldn't be too hard to find. The bottle it comes in is off-white. Mind you it's probably worth a try to test out some of the other insect repellent sunblocks too - they may work just as well or better.
Sincerely
Martyn Robinson
Hello Paul Malone,
I suspect that the leeches may still find a way inside no matter what you wear. There are, however, a few old and new tricks which might work for you. If you tuck the sleeves and trouser cuffs inwards, instead of outwards, on your arms and legs - and hold the cuffs in place with a few stiches - the doughnut shaped pocket they form can be filled with salt. As you walk your sweat dissolves some of the salt to run down over wrists and ankles making you an unpleasant host for any questing leeches. I've also been told that bicarbonate of soda will make them drop off if rubbed on them but have never used it on leeches (it works with ticks). Recently while covered in leeches along the Great North Walk we discovered that a certain sunscreen with an added insect repellent worked wonders at keeping them away and any brave ones who remained attached would drop off as soon as this lotion was applied to them using a small twig. We now don't go anywhere without it. Rub it on your feet and under your watch band before you dress for the day - and good luck!
Hello Wombat,
I think it is more a case of the right weather conditions rather than a breeding season for leeches. Warm, wet weather suits them very well but they are also out and about in cold wet weather too - just a bit slower! Dry and windy is the weather they hate most. As for treating your property to get rid of them that seems almost impossible to do as they have entered the Sydney suburbs in some areas and the owners have been battling them for years. As far as is known they are a nuisance rather than a health threat (although care should be taken that the bite wounds don't get infected). Some places that have rainforest walks have found certain products that can be applied along the pathways to keep the leeches away from these - you could ask these establishments what they use. Wholesale treatment of your land however is not recommended as it is more than likely to kill off a lot of beneficial animals instead - and you'll probably still have leeches at the finish. Interestingly there is one species of leech (a large rough skinned version) which feeds on the other blood sucking species and could be used as a biological control.
S
M
Hi Jupiter. This is an interesting question to which we don't have an answer as yet! I checked the Department of Medical Entomology site (Westmead Hospital/University of Sydney) to see what they say about mosquitoes (as they specialise in insects!) - they have an FAQ that says there is no evidence for HIV transmission in mosquitoes as the virus is so short lived and the blood sucking mechanism is separate from the saliva flow. I don't know if this is the same for leeches, but I suspect not as they are used in legitimate medical practices for tissue repair. However, as we are not medical experts, I can't say for sure! It'd be worth doing a bit of sleuthing on the net to find out...