Some earthworm species are not strong burrowers and live in the uppermost layer of soil in the litter layer. These earthworms are called epigeic species and they form shallow vertical burrows where they temporarily escape from drought, heat and disturbances.
Though small, earthworms are fighters. They have developed certain survival strategies which help them cope with nasty environmental conditions.
When the weather gets cold and the soil starts to freeze, earthworms move deeper down and overwinter in a state called aestivation. To aestivate, the earthworm generates a natural antifreeze and then curls up in a little knot. Earthworms also aestivate when conditions become dry or hot.
Of all the soil organisms, the earthworm has by far one of the most unique modes of reproduction. Earthworms are hermaphrodites, which means they have both male and female reproductive organs.
This brings us to one of the oldest myths about worms: that earthworms can fertilise themselves. Though some earthworms can fertilise themselves parthenogenesis , this is not the norm. Most earthworms require a mate of the same species to reproduce. You can tell when an earthworm is ready to mate because its clitellum will change colour from pinkish to red-orange. Here is the process of reproduction:.
Some earthworms mate on the soil surface and some earthworms mate in the soil. It has both male and female reproductive organs. That means I am neither a boy or girl, I am both.
When mating, another worm and I join together with heads pointing in opposite directions. Sperm is passed from one worm to the other and stored in sacs. The bristles hold a section of the worm firmly into the ground while the other part of the body protrudes forward. The earthworm uses segments to either contract or relax independently to cause the body to lengthen in one area or contract in other areas.
Segmentation helps the worm to be flexible and strong in its movement. If each segment moved together without being independent, the earthworm would be stationary. Digestive System The digestive system is partitioned into many regions, each with a certain function. The digestive system consists of the pharynx, the esophagus, the crop, the intestine and the gizzard.
After it passes through the esophagus, the food moves into the crop where it is stored and then eventually moves into the gizzard. The gizzard uses stones that the earthworm eats to grind the food completely. The food moves into the intestines as gland cells in the intestine release fluids to aid in the digestive process.
The intestinal wall contains blood vessels where the digested food is absorbed and transported to the rest of the body. Circulatory System Another important organ system is the circulatory system. The earthworm has a closed circulatory system. This band normally matches the color of the rest of the worm's body, but when earthworms are ready to mate, the band turns a darker shade. Although some species of earthworms will mate on the soil surface, this leaves them exposed to predators during this vulnerable time, so most worms mate underground.
The worms are thought to find one another through the release of pheromones. Once a partner is found, the two worms line up in opposite directions so that each worm's male opening lines up with the other worm's sperm receptacle, known as the spermatheca. The worms are then in position to exchange sperm. Once the worms have lined up, the male openings deliver sperm into the other worm's spermathecae. As this happens, the clitellum of each worm secretes mucous to make a tube that fills with a protein-rich fluid called albumin.
Once the sperm has been exchanged, the worms wriggle away. As they move, the tube slides off each worm's body. On its way, the tube passes the female reproductive pore and collects the eggs.
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