Parasites all live on or in other animals and many of them feed on blood. Blood is easy to collect whether you are inside or outside the body. It is highly nutritious and there is always lots of it, so the animal the parasite is feeding on can usually spare some. Leeches can be annoying and their bites can make us itchy but they are not usually dangerous to humans.
In fact, leeches have been used to treat human diseases for thousands of years. However, we now know that allowing leeches to suck blood does little to help in most cases. In fact, if too many leeches are applied, a sick person can get weak from loss of blood. The one area of medicine where leeches are still helpful is using them to improve blood circulation in the skin. They also reduce the chances of blood clotting when that could be dangerous in some sick people.
Leeches need blood to grow and reproduce, which they can do easily as all leeches are both male and female at the same time. But there's a lot more to them than just slimy bloodsuckers. Now, the leeches in this tank are medicinal leeches, and they've got this name for a really good reason. So for about 2, years up until quite recently, it was thought that the body's health was kept in balance by substances called humours which flowed through the body.
Now, blood was one of those humours. And if you had bad blood, or too much blood, then it needed to be drained. And that is where these guys came in. Draining the blood from the body was known as bloodletting. And using leeches to do this was the height of fashion in Victorian times. In fact, millions were used every year across Europe.
Leeches are actually worms related to the ones you find in your back garden. Leeches can attach themselves to prey using their mouth and tail. Leeches do all of their actual feeding through their mouth. They use their jaws to hold onto the host. The leech has sharp teeth in its mouth sucker, and it uses the teeth to sink in and attach to its prey to feed. Leeches feed until full, then they unhook their jaws and drop off the host.
Leeches can also attach to hosts using the sucker on their tails, or the posterior sucker. The posterior sucker helps the leech move quickly through the water and also helps the leech climb the host's leg.
Identification Leeches are segmented worms in the Subclass Hirudinea that are usually ectoparasitic. Habitat Most leeches are freshwater animals, but many terrestrial and marine species occur.
Distribution There are around 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. Feeding and diet Most leeches are sanguivorous, that is they feed as blood sucking parasites on preferred hosts. 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. 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.
Sensory organs Sensory organs on the head and body surface enable a leech to detect changes in light intensity, temperature, and vibration. 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.
Breeding behaviours As hermaphrodites, leeches have both male and female sex organs. The leech shrugs itself free of the cocoon, sealing it as it passes over the head. Leeches die after one or two bouts of reproduction. Economic impacts Medicinal use of leeches For over years, leeches were needlessly applied for many ailments as an adjunct to blood letting. Leeches are treated in the same way as blood products and are reused only on the same patient.
Leeches in Sydney suburbs The Sydney suburban sprawl is resulting in houses extending into areas such as wet valleys that leeches normally prefer. Predators Fish, birds and other invertebrates are the main predators on leeches.
Management Leech repellents The most common enquiry regarding leeches concerns repellents. Danger to humans The presence of hirudin in the wound following a leech bite may cause oozing to continue for several hours. Can leeches transmit disease? Andrew Thompson Reference Assoc. Back to top. Search website Submit Search.
0コメント