The Leech

Nov 16, 2008 Interesting Creatures in Guyana

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Leeches are annelids comprising the subclass Hirudinea which are regarded a species of fresh water, terrestrial and marine life form.
And like earthworms, leeches are hermaphrodites which mean that they are organisms that have both female and male reproductive organs (ovaries and testes respectively).
They reproduce by reciprocal fertilisation, and sperm transfer occurs during copulation. The leech exercising the role of the male will grow a sperm sack near the end of its tail and the leech playing the role of the female will bite it off, thus reproducing.
Also, similarly to the earthworms, leeches use a

clitellum to hold their eggs and secrete the cocoon.
During reproduction leeches utilise hyperdermic injection of their sperm. It is said that they use a spermatophore which is a structure containing the sperm.
Once next to another leech, the two will line up with their anterior side opposite the other’s posterior. The leech then shoots the spermatophore into the clitellur region of the opposing leech where its sperm will make its way to the female reproductive parts.
A leech’s body is composed of 34 segments and they all have an anterior (oral) sucker formed from the first six segments of their body, which is used to connect to a host for feeding and also to release an anaesthetic to prevent the host from feeling the leech.
Haemophagic leeches attach to their hosts and remain there until they become full at which point they fall off to digest. They use a combination of mucus and suction caused by concentric muscles in those six segments to stay attached and secrete an anti-clotting enzyme into the host’s bloodstream.
Some species of leech will nurture their young, while providing food, transport and protection, which is an unusual behaviour in an invertebrate.
The leeches are presumed to have evolved from certain Oligochaeta, most of which feed on detritus. However, some species in the Lumbricullidae are predatory and have similar adaptations as found in leeches.
Leeches have also been used for clinical bloodletting for thousands of years although most leeches do not feed on human blood but on small invertebrates which they eat whole.
Though all species of leeches feed on blood, not all species can bite; 90 per cent of them solely feed off decomposing bodies and open wounds of amphibians, reptiles, waterfowl, fish, and mammals (including, but not limited to, humans).
A leech attaches itself when it bites, and it will stay attached until it has had its fill of blood. Due to an anticoagulant (hirudin) that leeches secrete, bites may bleed more than a normal wound after the leech is removed. The effect of the anticoagulant will wear off several hours after the leech is removed and the wound is cleaned.
Leeches normally carry parasites in their digestive tract which cannot survive in humans and do not pose a threat. However, bacteria, viruses, and parasites from previous blood sources can survive within a leech for months, and may be retransmitted to humans. A study found both HIV and hepatitis B in African leeches from Cameroon.
Starting from the anterior sucker is the jaw, the pharynx which extends to the crop, which leads to the Intestinum, where it ends at the posterior sucker. The crop is a type of stomach that works like an expandable storage compartment. The crop allows a leech to store blood up to five times its body size; and because the leech produces an anti-coagulant, the stored blood remains in a liquid state.
One recommended method of removal is by using a fingernail to break the seal of the oral sucker at the anterior end (the smaller, thinner end) of the leech, repeating with the posterior end, then flicking the leech away. As the fingernail is pushed along the person’s skin against the leech, the suction of sucker’s seal is broken, at which point the leech should detach its jaws.
A common but medically inadvisable technique to remove a leech is to apply a flame, a lit cigarette, salt, soap, or a caustic chemical such as alcohol, vinegar, lemon juice, insect repellent, heat rub, or certain carbonated drinks. These cause the leech to regurgitate its stomach contents into the wound and quickly detach. The vomit may carry disease and increases the risk of infection.
Simply pulling a leech off by grasping it can also cause regurgitation, and adds risks of further tearing the wound, and leaving parts of the leech’s jaw in the wound, which can also increase the risk of infection.
An externally attached leech will detach and fall off on its own when it is satiated on blood, usually in about 20 minutes (but will stay there for as long as it can), while internal attachments, such as nasal passage or vaginal attachments, are more likely to require medical intervention.
After removal or detachment, the wound should be cleaned with soap and water, and bandaged. Bleeding may continue for some time, due to the leech’s anti-clotting enzyme. Applying pressure can reduce bleeding, although blood loss from a single bite is not dangerous. The wound normally itches as it heals, but should not be scratched as this may complicate healing and introduce other infections. An antihistamine can reduce itching, and applying a cold pack can reduce pain or swelling.
Some people suffer severe allergic or anaphylactic reactions from leech bites, and require urgent medical care. Symptoms include red blotches or an itchy rash over the body, swelling away from the bitten area (especially around the lips or eyes), feeling faint or dizzy, and difficulty breathing.
There is no guaranteed method of preventing leech bites in leech-infested areas. The most reliable method is to cover exposed skin. The effect of insect repellents is disputed, but it is generally accepted that strong (maximum strength or tropical) insect repellents do help prevent bites.
(Source: Wikipedia the Free Online Encyclopedia)

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