Earthworms are the largest cylindrical segmented worm in the Oligochaeta class. The earthworm’s body looks like a small tube, and has a muscular, slimy, and moist outer body. It is annular, and has a very simple circulatory system. It has 2 main blood vessels throughout the length of their long body, where a ventral blood vessel which leads blood to the posterior and a dorsal blood vessel that leads to the anterior. The blood is distributed into a vascular sinus in the gut wall where gases and nutrients are exchanged from the abdominal veins into various capillaries on the body wall and other organs. This arrangement includes supraoesophageal, suboesophageal, parietal, and neutral veins.
They are hermaphrodites where they typically have testes surrounded by testes sacs. There are 2 to 4 pairs of seminal vesicles which the male side of the earthworm will produce, store, and release the sperm. They also have ovaries and ovipores, where the female pores will release eggs. However, most earthworms also have one or more pairs of spermathecae which are internal sacs that will both receive and store sperm during mating, and some species of earthworms do transfer their sperm using external spermatophores.
Earthworms usually eat undecayed leaves and other plant matter. They are an important animal as it plows the soil by tunneling through it, and enriches the soil with its waste products. The passageways in the soil will circulate air and water through it, and therefore earthworms are a favourite of gardeners worthwhile as earthworms create good soil. There can be as many as 1 million earthworms per acre in good soil.
They may be found on the ground surface after excessive rain. Earthworms need a wet environment both for respiration and comfort. If the soil during the rainy season becomes saturated, and earthworm may have trouble breathing and will begin to drown. Also, if the surface is unexpectedly paved, rocky, or somehow hardened, they may become stranded and die due to injury, exposure, dehydration, or predation.
Earthworms also come to the surface during the rainy season in order to mate, although there are only a few species that come to the surface to mate and may become stranded. Another theory is that the earthworm may be using the soggy conditions on the surface to travel much faster than they can underground. They will not become dehydrated rapidly since the temperature on the surface is cooler during and after the rain. However, this is considered risky behaviour when it is done in the late evening, summer, or during the day time as earthworms die quickly when they are exposed to direct sunlight. In addition, they are also vulnerable to predators. Earthworms are preyed upon by many species of snakes, birds, mammals, and invertebrates as they form the base of many food chains.