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 species that feed on blood have special chemicals in their saliva that prevents blood-clotting.
Many blood-feeding leeches attack only fish , a few attack any vertebrate including people , and a few are specialists on another group of animals, like turtles or waterbirds. There are also lots of leech species that don't suck blood.
They are predators, eating worms , snails , aquatic insects , and other invertebrates. This craze led to a rather absurd battle between rival pharmacies, who produced increasingly elaborate leech jars in order to entice customers to choose their product.
They were ridiculous, huge, over the top, and not really even practical for storing the escape artist leeches at all. But ultimately it was all about appearances, and a more eye catching display meant more customers. Here's some photo examples of this madness. This historic use of leeches severely reduced medicinal leech Hirudo medicinalis populations across Eurasia, so this species is now protected.
Today, leeches are still kept for use in both human and animal medicine around the world and are approved by the US Food and Drug Administration FDA as " medical devices ". The hospitals keep leeches to make use of this blood-vessel clearing ability. These leeches are sourced from captive bred populations raised in controlled environments, to help minimise the potential risk of infection.
Leeches are another of the segmented worms but, unlike earthworms which are hidden from view in the soil, no effort is required to find leeches - they are very good at finding you. Not all leeches are interested in warm blooded animals with some being more interested in sucking the juices out of snails and other worms. When their preferred prey is not found, leeches will feast on other choices such as fish, frogs, turtles or birds.
Leeches are sensitive to changes in light and other stimuli and they stand erect and wave their body around to pick up the sensations from an animal. Then they use the inchworm crawling technique to head for their target.
If you'd like to observe this first hand, sit down on the rainforest floor and then watch the ground around you closely. Leeches also find their food by accident, say when a bushwalker brushes past. Leech bites are annoying but it is believed that they do not transmit any diseases, so they really aren't as bad as other biting pests. They feed by sucking blood or body fluids from their host and this is made easier by the anti-coagulant they squirt into the wound.
Their saliva also has a numbing agent to desensitise the victim's skin so that the bite isn't noticed. This is why the leech is normally not discovered until it has finished its meal and the trickle of thinned blood from the wound is noticed. Some people seem to be allergic to leech bites and experience a delayed itching followed by a scar which takes many months to fade away. You can read lots more about leeches in the two factsheets below:.
Tropical gardeners know flatworms as the colourful but slimy worms that are found under rotting wood or vegetation in the compost bin. 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. 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.
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