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Blood Sucker’s Swamp

In this activity, students explore how leeches feed and travel, through this fun and interactive game.

Leeches are annelids found in mostly in freshwater and damp environments. They have soft, muscular, segmented bodies that can lengthen and contract, This extreme elasticity of the leeches' body allows them to expand and contract their muscles to move.

Leeches have two suckers; one on each end, and use them for locomotion and feeding. The rear sucker is used primarily for locomotion. This sucker also helps the leech hold onto its host while getting a blood meal.

Leech movement

The feeding sucker also helps the leech to move and hold on, but its main function as the location of the mouth, is blood sucking! The outer ring of the leech's jaw, located in the forward sucker, is very muscular and latches on. The inside of the jaw is lined with rings of saw-like teeth that, penetrate the skin, dig into the flesh of the host and begin the blood flow for a meal.

The saliva of the leech contains a powerful anticoagulant- a chemical that keeps the blood flowing (blood naturally contains material that helps it clot and stops bleeding, so that we don't bleed to death every time we get a paper cut.) Other chemicals in the saliva act to numb the bite area, so often there is no discomfort while the leech feeds. Leeches feed until they are full, then detach and digest the blood, which they need as food, and to reproduce (although most leeches are hermaphrodites, they need to cross fertilize). Large volumes of blood, up to several times the weight of the leech, can be stored in a crop in the pharynx (a widening of the alimentary canal) before digestion begins.  Remember- a large meal for a leech is a tiny amount of blood for most animals to lose!

Leeches, like terrestrial worms, are an important part of aquatic ecosystems, both as predator AND prey. A lot of other critters will make a meal out of leeches: fish, turtles, shore birds, herons, etc. Leeches don't have it all their own way, they're just part of the food chain.

Vocabulary:

Annelid: worms or wormlike animals of the phylum Annelida, characterized by an elongated, cylindrical body divided into ringlike segments, including earthworms, leeches, and polychetes (marine worms).

Anticoagulant: chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time.

Alimentaty canal: the whole passage along which food passes through the body from mouth to anus. It includes the pharynx, esophagus, stomach, and intestines.

Elasticity: The tendency of an object to return to its original shape after being stretched or compressed.

Hemaphrodite: an organism that has complete or partial reproductive organs and produces gametes normally associated with both male and female sexes.

Objectives

  • Describe how animals, other than humans, feed and travel.

Materials

  • Per Class:
    5-10 leech face masks (use pinneys as an alternative)
    approximately  40 small balls
    6 hula hoops

Key Questions

  • Why do leeches latch onto animals and humans?
  • How could having lost blood to a leech hamper a human or animal?
  • How is a greater leech load more of a problem?
  • What other animals do you know of that eat blood? (Even humans eat cooked blood!)

What To Do

  1. Divide a gym or field into two sides with a rope or line, and set up 3 hula hoops at the ends of each side. Put the same number of balls into the hoops of each team.
  2. Divide class into three groups: two teams of swamp explorers and one group of blood sucking leeches (with masks). The students are encouraged to name their groups and work together as a team.
  3. The swamp explorers run back and forth, capturing “treasure” (balls) and bringing it back to their hoops. Students are NOT allowed to protect their “treasure” (hula hoop and balls) and they can only carry ONE BALL AT A TIME. This means that the focus of the game is on team work and speed. Give the teams a timed trial run to let them get the hang of working with their team.
  4. Now start the real game by sending out the leeches. The leeches attach to the swamp explorers by gently holding their shoulders from the back. The explorers cannot get rid of the leeches and may accumulate more than one. Leeches cannot stop the explorers completely but they can and will slow them down.
  5. The winning team will have collected the most balls once the end whistle blows.

Extensions

  • Find out:Howto remove a leech. How often leeches feed. Whether leeches live in your area.
  • Explore Leeches in medicine.

Other Resources

Curious Kids | Why do leeches such our blood?

NPR| See how leeches can be a surgeons sidekick

DEEPLOOK | Video | Take Two Leches and Call me in the Morning