Earthworms are big segmented worms that belong to the Phylum Annelida, Class Clitellata, and sub class Oligochaeta. Leeches are also worms belonging to the same Phylum and class, but sub class Hirudinae and are of three types, freshwater, terrestrial and marine. The similarities and differences between earthworms and leeches are outlined below.
Comparison chart
 | Earthworm | Leech |
|---|---|---|
 |  | |
| Classification | Earthworms are big segmented worms that belong to the Phylum Annelida, Class Clitellata, and sub class Oligochaeta. | Leeches are also worms belonging to Phylum Annelida, Class Clitellata and sub class Hirudinae |
| Anatomy | Earthworms have a segmented (37-100) tube-like muscular body connected by a continuous gut, a nerve and a blood vessel. | The body of a leech is divided into 34 segments with a small anterior and large posterior sucker. |
| Feeding and Nutrition | Earthworms feed on organic matter found in the soil such as dead leaves and small soil particles that are digested in the intestine. | Some species of leech (hematophagus) feed on blood. Other species feed on decomposing bodies and open wounds of amphibians, reptiles, fish and even mammals. |
| Reproduction | Earthworms are hermaphrodites and have two pairs of testes surrounded by testes sac, ovaries and ovipores. During copulation sperms are exchanged between two worms and stored. Reproduction takes place after copulation. | Leeches are also hermaphrodites with both male and female reproductive organs. Reproduction occurs after copulation and is followed by cocoon formation in which the embryos develop. |
| Locomotion and Behaviour | Earthworms mainly live in the soil. They move by means of contraction and relaxation of muscles which shorten and lengthen the body and aids in movement. The setae (bristles) on the segments along the body and mucus secreted also aid in this movement | Leeches are of three types -freshwater, terrestrial and marine. Leeches move with the help of the anterior and posterior suckers and longitudinal muscles along the length of the body. |
| Benefits | Earthworms aerate the soil while burrowing, feed on organic matter and increase its fertility in the process by adding humus to the soil. Fresh earthworm casts are rich in nitrogen, phosphates and potash. | Leech therapy (or Hirudotherapy) has been used in some areas of medicine such as plastic and reconstructive surgery to remove swelling and congestion in tissues and blood vessels. |
| BY | Basanta | Rijal |
| Structure | Earthworms are thin, elongated & round in structure & white in colour | Leeches are flat & short in structure & black in colour |
| Asexual Reproduction | Earthworms can regenerate for asexual reproduction | Unlike other Annelids, Leeches only reproduce sexually but can't regenerate |
Differences in Anatomy
Earthworms have a segmented tube-like body connected by a continuous gut, a nerve and a blood vessel. The number of segments varies in different species from 37 up to 100 segments. The outside body is slimy and muscular.
The body of a leech is divided into 34 segments. The first 6 segments form an anterior oral sucker which is used to attach to the body of the host. A large posterior sucker is also found at the posterior end which helps in the locomotion of the animal. From a distance, a leech can resemble a slug.
Differences in Diet
Earthworms feed on organic matter found in the soil such as dead leaves. They also ingest small soil particles that are digested in the intestine.
Some species of leech (hematophagus) feed on blood. Other species feed on decomposing bodies and open wounds of amphibians, reptiles, fish and even mammals. Hematophagus leeches can bite, suck out blood from the host, secreting an aesthetic to an anti-clotting enzyme into the blood. As a result, leech bites bleed longer than normal wounds.
Reproduction of Leech vs Earthworm
Earthworms are hermaphrodites which mean that it has both male and female reproductive organs. The worms have two pairs of testes surrounded by testes sac, which produce and store sperms, ovaries and ovipores in segment 13 and some species use spermathecae or internal sacs to store sperms from other worms at the time of copulation. Other species have spermatophores, externally located where the sperms from other worms are stored. During copulation sperms are exchanged between two worms and stored. Reproduction takes place after copulation when the eggs and sperms (from the second worm) are injected into the cocoon. During this process, the clitellum turns pinkish red and is responsible for secreting the cocoon. The sealed cocoon forms a melon-like structure in which the embryos develop. The earthworm takes about a year to grow into its full sixe. Sex structures develop 60-90 days after hatching. The average life span of earthworm varies from 2-8 years, garden varieties having a shorter lifespan then field varieties. Some species of worms reproduce by asexual means or parthenogenesis and form clones.
Leeches are also hermaphrodites with both male and female reproductive organs. Reproduction occurs the same way as in earthworms, except that the sperms are stored in spermatophores, which are sacs outside the body of the leech. Copulation is followed by reproduction and cocoon formation.
Differences in Locomotion and Behaviour
Earthworms live in the soil and can be usually seen on the surface after a heavy storm. They move by means of contraction and relaxation of muscles which shorten and lengthen the body and aids in movement. The setae or bristles on the segments along the body and mucus secreted also aids in this movement.
Leeches lack setae, and move with the help of the anterior and posterior suckers and longitudinal muscles along the length of the body. The posterior sucker latches on to the surfaces and while the longitudinal muscles elongate and move the body of the leech forward, after which the anterior sucker attaches to the surface and the posterior one is detached.
Video:Giant Earthworm vs Japan Mountain Leech
Benefits
Earthworms aerate the soil while burrowing, which is highly beneficial for the soil as it helps in nutrient and water uptake by the plants. Also, some species of earthworms feed on organic matter like dead leaves in the soil, and thus help in increasing its fertility in the process by adding humus to the soil. Fresh earthworm casts are rich in nitrogen, phosphates and potash.
Leech therapy (or Hirudotherapy) has been documented in some olden texts. In recent years, leeches have been used in some areas of medicine such as plastic and reconstructive surgery to remove swelling and congestion in tissues and blood vessels.
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