Saturday, September 29, 2007

Leeches(more Fact)

What do they look like?

Leeches are segmented worms with suction cups at each end. Their bodies are flattened, much wider than they are thick. They are usually dark colored, often brown or sometimes yellow or dark green. Some species have no markings, others have spots and stripes. The smallest leeches grow no more than 5 mm, but some big species may get to be more than 25 cm long. Many leech species have one or more pairs of eyes visible on the top of their front end. Leech species that suck blood have sharp teeth. Predatory species may have teeth, or may have only crushing jaws.

What kind of habitat do they need?

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.

How do they grow?

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.

In most species, each leech has both male and female sex organs, and can both lay eggs and give sperm to another worm. After mating, each worm produces several cocoons containing eggs. The cocoons are protected with a tough layer of protein, and contain one or a few eggs (depending on the species). Most species attach their cocoon to vegetation or debris underwater, but a few put them in damp soil. Leeches reproduce and grow at very different rates, depending on which species they are, the amount of food they get, and the temperature of the habitat they live in. Most grow faster in warmer temperatures.

How long do they live?

Some leeches complete their life cycle in a few years.

How do they communicate with each other?

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.

What eats them and how do they avoid being eaten?

Known predators

* fish ( eat leech eggs )
* birds
* large aquatic insects
* snakes
* other leeches
* snails (eat leech eggs)
* mites (eat leech eggs)

Most leeches hide while resting, staying in thick plant growth or hiding in mud. Many leech species are nocturnal ( active at nite), this helps them avoid predators and locate resting prey. If attacked, some species swim away as fast as they can, others go limp and "play dead," others curl into a ball and sink to the bottom. When parasitic leeches attach to their host, they sometimes select places that are hard for their host to reach.

What roles do they have in the ecosystem?

Leeches are sometimes important members of aquatic food webs. They are mid-level consumers, eating smaller animals and in turn being eaten by larger predators.