Although some leeches consume small insects and larvae whole, this species is mainly a hematophage, meaning that it feeds on blood. The hematophagic leeches feed on invertebrates, fish, frogs, and, notably in the Mountain Lake pond, snapping turtles. Snapping turtles have been found here with more than eight leeches attached to them. They also feed on warm-blooded creatures when the opportunity arises. Although leeches, especially large ones can be a significant health detriment to smaller animals, they are not harmful to most large animals.
A leech can ingest several times its weight in blood from one host before dropping off and not feeding again for weeks, or even months. Leeches inject hirudin, an anesthetic, to keep the hosts from feeling them break the skin. They also inject an anticoagulant to keep the blood from clotting so that they can feed. Some of the most common predators of leeches include turtles, fish, ducks, and other birds. 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. 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 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.
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. 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.
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 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. For over years, leeches were needlessly applied for many ailments as an adjunct to blood letting. Their use in Europe peaked between and , 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.
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. 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. 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.
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. There is no evidence to suggest that they do. The presence of trypanosomes in the gut of jawless leeches has been noted, but jawed leeches do not appear to be hosts. Marine leeches feed on other aquatic life forms that share the murky ocean depths.
Leeches can be found feeding in just about all the world's oceans. Notostomum laeve is the first recorded marine leech species found in North America. It lives in the icy waters of the Arctic Ocean. Leech expert Dr. Mark Siddall has noticed that marine leeches by species feed on either bony or cartilaginous fish. Members of one leech species are never found feeding both types of fish.
Some leeches manage to live on land rather than in water, but only if the environment is high in humidity -- all leeches need high moisture to maintain their protective covering of mucus.
Land leeches live in the moist soils of rain forests in places like South America, Africa and Asia. The extremely rare Americobdella valdiviana in Chile is a terrestrial leech that feeds on earthworms. They and all other terrestrial leeches are specially adapted to life on land but can survive submerged in water for short periods.
If conditions are quite dry they can burrow in the mud and aestivate there until moisture revives them. Aside from their geographic location and diet, leeches are differentiated by their mouths.
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