Earthworms

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Earthworms

• There are over 3,000 species of earthworms around
  the world. These invertebrates (animals without a
  backbone) range in color from brown to red, and
  most have a soft body. Earthworms range in size
  from a few inches long to over 22 feet long. The
  largest earthworms live in South Africa and
  Australia.

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Lumbricus terrestris

• Earthworms (also called nightcrawlers) are very
  important animals that aerate the soil with their
  burrowing action and enrich the soil with their
  waste products (called castings). Good soil can
  have as many as 1,000,000 (a million) worms per
  acre.

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Earthworm Body Systems

• The most well-known annelids are earthworms. They
  have a definite anterior, or front end, and a
  posterior, or back end.

• Earthworms have more than 100 body segments. The
  segments can be seen on the outside and the
  inside of the body cavity.

• Each body segment, except for the first and last
  segments, has four pairs of setae.

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How do earthworms breathe?
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What do worms eat?

• Earthworms get their nutrition from many forms of
  organic matter in soil. They eat decaying roots
  and leaves, tiny organisms that live in the soil,
  bacteria, and fungi. Worms also feed on the
  decomposing remains of other animals. An
  earthworm can consume up to one-third of its own
  body weight in just one day!

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How do worms eat?

• As an earthworm burrows through the soil, it
  takes soil into its mouth.

• The soil ingested by an earthworm moves to the
  crop, which is a sac used for storage.

• Behind the crop is a muscular structure called
  the gizzard, which grinds the soil and the bits
  of organic matter.

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Digestion and Excretion

• This ground material passes to the intestine,
  where the organic matter is broken down and the
  nutrients are absorbed by the blood.

• Wastes leave the worm through the anus.

• Their wastes pile up at the openings to their
  burrows.

• These piles are called castings which help
  fertilize the soil.

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Earthworm burrow - castings
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Earthworm burrow
This picture was taken at a research site. The
tape is measuring the depth of an earthworm
burrow.
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Circulatory System how blood flows

• Earthworms have a closed circulatory system.

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Nervous System

• Earthworms have a small brain in their front
  segment.
• Nerves in each segment join to form a main nerve
  that connects to the brain.
• Earthworms respond to light, temperature and
  moisture.

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Specialized Cells

• Earthworms have no eyes or ears, but they have
  light-sensitive cells that help them tell the
  difference between light and darkness.
• Their bodies are sensitive to vibrations and
  worms may "outrun" the shovels of anglers digging
  worms for fish bait!

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How do worms reproduce?

• Earthworms are hermaphrodites (hur MA fruh
  dites)meaning they produce sperm and eggs in the
  same body.

• Even though each worm has male and female
  reproductive structures, an individual worm cant
  fertilize its own eggs.

• Instead, it has to receive sperm from another
  earthworm in order to reproduce.

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Earthworms are hermaphrodites
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History of Earthworms

• During the time that glaciers covered much of
  North America, earthworms disappeared from the
  frozen soil. It would have taken centuries or
  longer for earthworms to become re-established on
  their own, but human actions speeded up the
  process.
• Farmers and gardeners brought potted plants from
  other places for planting, releasing earthworms
  that were in that soil.
• And when farmers tilled the soil to make it
  easier for tiny roots to grow, they also made it
  easier for the worms to tunnel through the soil.
  As worms increased, so did robins.

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Middle of the Road

• If a naturalist from another galaxy came to Earth
  with the assignment of collecting an "average
  Earth-animal," after studying everything from the
  lowliest sponges, jellyfish, and flatworms, to us
  humans, there would be a fair chance that
  he/she/it would choose to take back an annelid.
  In other words, segmented worms stand about
  midway between the simplest and most complex of
  Earth's animals.

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Value of Segmented Worms

• Earthworms help aerate the soil by constantly
  burrowing through it.

• Earthworms speed up the return of nitrogen and
  other nutrients to the soil for use by plants.

• Researchers are developing drugs based on the
  chemicals that come from leeches because leech
  saliva prevents blood clots.

• Marine worms and their larvae are food for many
  fish, invertebrates, and mammals.

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Not always a good guy!

• Earthworms are sometimes considered an invasive
  species in northern temperate forests.
• This is because of their ability to change the
  soil structure and nitrogen levels.
• Invasive non-native species are of concern to
  ecologists because they can change the
  environments they invade.