Most leech species are found in shallow, slow-moving freshwater, but some live in the oceans, and a few live in moist soil on land. Leeches lay eggs in cocoons, and the babies that hatch out look and behave like little adults.
They don't change much as they grow, they just get bigger. Leeches that live in habitats that freeze or dry out during part of the year bury themselves in mud and stay dormant until the habitat improves. Leech growth rate is strongly affected by temperature and food supply. Most species can mature in a few weeks or months if conditions are good.
Some leeches complete their life cycle in a few months, but many can live for several years. All leeches can crawl, and some are good swimmers. They search for prey by following the scent or touch of the animals they want to eat. When they first detect food, they extend their bodies and hold very still, probably to carefully sense their prey. Leeches have very poor vision often they can only tell the strength of light , but are very sensitive to touch. They also have a strong sense of taste.
They cannot hear, but are sometimes very sensitive to vibrations. They communicate with other leeches chemically, and by touch. Leeches are famous as blood-suckers. 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. Trypanosomes cause the African sleeping sickness in humans.
Leeches transmit trypanosomes that infect fish, crocodiles and even platypus, but none of them are dangerous to humans. Allergy to leech bite has been reported. Medical opinion should be sought, depending on the severity of the reaction. Trypanosomes of Australian mammals: A review Craig K. Thompson , Stephanie S. Godfrey, R.
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.
They are hermaphrodites, and reproduce through reciprocal fertilization, in which both leeches become impregnated at the same time. The mother leech forms a tough, gelatinous cocoon around the egg mass and attaches it to a hard object or buries it in the mud. The cocoon contains all the nutrient that the young leeches need to survive, and the young emerge several weeks later.
Some species nurture their young, which is unusual among annelids. However, most leeches only reproduce once or twice in their lifetimes. Leeches are not capable of regeneration and can only reproduce sexually. Although leeches are mainly nocturnal, they are attracted to disturbances in the water which might indicate food sources.
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