Drawing On Science by Steve Yaeger
Drawing On Science by Steve Yaeger
I get all kinds of science questions from my grandkids, nephews, and nieces and the other day one of my nephews asked, "Are there any animals that don’t have bones?" I gave him his answer and his question gave me the idea for this week’s subject.
There are thousands of different kinds of worms. (Yes, they are one of the many animals having no bones.) They range in size from very small to very large. Some live in the oceans, others live in lakes. Some live in sand, others live in mud. Some live in our backyard soil and these are the worms with which we are most familiar. People think of earthworms as slimy, squirmy, wet, wriggling, and yucky things, but they are important to the environment.
Earthworms belong to the group of animals known as Annelids (AHN-na-lids). Annelids are segmented worms because their bodies are divided into similar parts or segments. Worms feel slimy because their bodies are covered with mucus, which is similar to what comes out of your nose when you have a cold. The mucus is necessary because the skin has to be kept moist so that the worm can breathe. You see the earthworm has no lungs or gills. Oxygen from the air must pass through its moist skin into its body and then into the blood. Carbon dioxide has to go in the opposite direction. Too much moisture, however, can drown the worms. That’s why we see them on the surface of the soil or sidewalk after a heavy rain. Their tunnels become flooded, so they have to escape being drowned.
In the scientific world earthworms are called Lumbricus terrestris (LUM-brah-cus ter-RES-tris). The worm has four pairs of setae (SEY-tay) on each of its body segments. Setae are stiff bristles used to anchor the worm when it is burrowing through the soil. As it moves forward it eats dead bugs, leaves, twigs, and, of course, dirt. Now you may think that’s gross, but to an earthworm such a meal is like you eating chicken fingers and French fries.
Just behind the mouth is a pharynx (FAH-rinks), which looks sort of like a bulb. It has muscles and acts like a pump. The food is sucked into the mouth by the pumping action of the pharynx. To make the food easier to move, the pharynx produces mucus, which covers the food to make it slippery. Now the food enters the esophagus (a-SAH-fa-gus). The esophagus is divided into a crop and a gizzard. The crop is used to store food. The gizzard is like a grinding machine. It is very muscular and it has a hard skin on the inside. The gizzard’s muscular action grinds the food into smaller pieces. Then the food is passed on into the intestine where the nutrients are absorbed into the blood for distribution throughout the body. Anything not digested is waste and is excreted (=gotten rid of) through the anus. You would call this poop, but it is known as castings. It is the castings and the tunnels of earthworms that keep the soil in good, healthy condition for growing things. Castings are really recycled soil. Tunnels or burrows are the result of the earthworms’ feeding activity and they let air mix with the soil. So the worms are natural decomposers or recyclers. The worms spend most of their time in the tunnels, which may have two openings with vertical as well as horizontal branch tunnels. In winter or during dry periods earthworms burrow deeper into the soil.
Earthworms have nerves and a brain. They have no eyes, but they do have photoreceptors. These are light-sensitive organs found under the skin. The worms are sensitive to strong light and prefer weak light or darkness. They are also sensitive to touch.
There are no male or female earthworms. They are hermaphrodites (her-MA-fro-dights). Each worm has both male and female reproductive organs. The organs are found in the clitellum (cli-TEL-lum), a light-colored band found not far from the worm’s head. When they are mating two worms join together with each worm facing in the opposite direction. A coat of mucus is formed, which surrounds the worms. Sperm is passed from one worm to the other worm. Then they separate. A few days later the clitellum forms an ovoid-shaped (=like an egg) cocoon. The cocoon, much like a cigar band, slowly slips past the anterior (=front) part of the worm. As this is happening sperm and eggs are deposited in the cocoon. The open ends of the small, yellowish cocoon are sealed and fertilization occurs. In two to three weeks one egg hatches and the baby worm leaves the cocoon to make its way through life.
Cleopatra, the last pharaoh of Egypt, knew that earthworms were important to the soil. In 50 BCE she said they were sacred. Earthworms can live up to twenty years if they are not squooshed, dried up, used as fish bait, or cut up. By the way if an earthworm is cut in half it does not grow into a new worm or grow new parts (=regeneration)—it just dies.
Questions? Email Steve: Drawingon email@example.com