Ecosystem Connections Humans are naturally repulsed by squishy bloodsuckers, but parasitism is an ancient way of life for many animals on Earth, and there is much to say for it. Who isn't repulsed by leeches! Yet once you get past the fact that many species are parasitic bloodsuckers, you will discover that they are fascinating creatures. Right to Use. Leeches, which are worms, and water pennies, which are beetles, both have segmented bodies.
Some leeches specialize in certain kinds of hosts while others are generalists. This leech is hanging from a turtle's hind leg. Similar Species. Turbellarians Planarians; Free-Living Flatworms. Tubificid Worms Tubifex Worms. Horsehair Worms. Crane Fly Larvae. 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. Jawed leeches Gnatbobdellida have teeth they use to latch onto their prey for bloodsucking.
Jawless leeches Rhyncobdellida use a proboscis -- or long, thin mouthpart -- to pierce their victims and draw blood. These leeches most typically feed on other small aquatic animals like snails and other worms. The giant Amazonian leech Haementeria ghilianii , which grows up to 18 inches long, is an example of a jawless leech. Worm leeches Pharyngobdellida do not suck blood. The Australian land leech has only two jaws and makes a V-shaped incision.
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. There are around species of leeches world wide.
These are divided into two major infraclasses. 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.
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. 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. 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. Leeches are infamous for sucking blood from people and other mammals, but thse are rare in Britain and Ireland and very unlikely to be found in gardens.
Piscicola geometra is up to 80mm long, slender with a cylindrical body section, and large anterior and posterior suckers. It spends much of its time rigidly extended, resting like a rod with its rear sucker attached to a plant. They swim strongly in a whip-like motion when they detect a fish, to which they attach, and pierce the skin with their mouthparts, and ingesting blood.
Predatory leeches. Although globally most leeches are blood parasites,most of those in Britain and Ireland are predators, feeding on tadpoles, insects and pond snails. We have three species of Glossisiphonia of which G. It is up to 30mm long and feeds on snails. Erpobdella octoculata is a common species which swallows small living prey such as larvae of the fly Chironomus whole, but will also suck body fluids from wounded larvae and all manner of dead and decaying freshwater organisms, so is a scavenger too.
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