1. Helps in soil fertility.
Earthworms form burrows through the soil seeking carbon rich zones (e.g. dead plant residues), and these burrows serve as preferential paths for water flow and gas transport in soil. They burrow during the day—typically keeping close to the surface—capable of digging down as deep as 6.5 feet. The worm's first segment contains its mouth. As they burrow, they consume soil, extracting nutrients from decomposing organic matter (like leaves and roots) and make the soil fertile. So they are called "farmer's friends".
2. They are hermaphrodites.
Earthworms are hermaphrodites: each carries male and female reproductive organs. When mating, two individual earthworms will exchange sperm and fertilize each other's eggs. Each individual has both male and female genital pores. Earthworm mating typically occurs after it has rained and the ground is wet. Sperm and egg of an individual earthworm mature at different times.
3. Respire through skin.
They breathe through their skin. Air dissolves on the mucus of their skin, so they must stay moist to breathe. If worms dry out, they suffocate. As fresh air is taken in through the skin, oxygen is drawn into the worm's circulatory system, and the worm's hearts pump the oxygenated blood to the head area. Earthworms lack specialised respiratory organs. Except for the first three anterior segments and the last posterior segment, all body segments include nephridia. They use nephridia, coiled tubular duct-like organs that filter and eliminate waste from their bodies, made of apertures that extend to the skin. Each segment can expel waste gases through these openings in the earthworm’s skin.
4. Nocturnal
Earthworms are active at night. During night hours they come out of their burrows in search of food, reproduction and exploring fresh habitat.
5. Sense organ
The earthworm's body is covered with chemoreceptors. These are cells that allow the earthworm to taste things and are tiny sense organs which detect chemicals in the soil. The muscles make movements in response to touch and taste.They sense light through specialized cells in their head. Because they can sense light, many worms avoid surfacing while the sun is out. Night crawlers get their name from the fact that they typically emerge from the ground during the night hours.
6. Closed circulatory system.
The earthworm has a closed circulatory system. An earthworm circulates blood exclusively through vessels. There are three main vessels that supply the blood to organs within the earthworm. These vessels are the aortic arches, dorsal blood vessels, and ventral blood vessels.
7. Brain of earthworm.
All earthworm operations are regulated by the nervous system, but not necessarily by the brain. They have both sensory and motor neurons, like larger animals. In earthworm, cerebral ganglions function as a simple brain which is located above the pharynx and is connected to the first ventral ganglion the removal of which would result in uncontrolled movement of the worm.Stimuli or sensory impulses are conducted to the ventral nerve cord from the receptor through sensory fibers, from where motor impulses are reflected along efferent fibers to contracting muscles. A simple reflex arc forms the circuit of stimuli or impulses.
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