Living where land and water meet fiddler crabs
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Lesson 5 - PowerPoint PPT Presentation

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Living where land and water meet: Fiddler Crabs. Lesson 5. Materials. Prepare salt water by filling a pail with water, add drop of conditioner, add 2 pinches of Instant Ocean, stir 4 ½ cups of sand mixed with 4 ½ cups of humus, mix, remove sticks China marker Tape Tank with lid Water bowl

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  • Prepare salt water by filling a pail with water, add drop of conditioner, add 2 pinches of Instant Ocean, stir

  • 4 ½ cups of sand mixed with 4 ½ cups of humus, mix, remove sticks

  • China marker

  • Tape

  • Tank with lid

  • Water bowl

  • Paper towel

  • Hairgrass

  • Cup with lid

  • Ruler


  • Review necessary elements of a habitat for Fiddler Crabs

  • Create habitat

  • Record living and nonliving elements in habitat

  • Discuss how to take care of the Fiddler Crab

  • Discuss feeding schedule

  • Observe crabs and record questions


  • Along the shore of almost any body of seawater, you can spot a variety of crabs.

  • Crabs are crustaceans, animals whose bodies are covered by hard shells, or exoskeletons.

  • Crustaceans also include lobsters, crayfish, and shrimps.

  • Crustaceans are a subgroup of larger group of animals known as arthropods – the most abundant macroscopic animals on Earth.


  • Crustaceans have segmented bodies and jointed appendages.

  • An appendage is any part that extends out from an animal’s body, such as legs, feelers, and mouth parts.

  • All crustaceans have armor-like exoskeletons with flexible joints.

  • Muscles inside of and attached to the exoskeleton give these animals great strenth.

Fiddler crab
Fiddler Crab

  • Most crabs live in or near the sea, either in shallow tidal mud flats or in the depths of the ocean.

  • Most crabs breathe with gills.

  • Lay eggs in a wet environment

  • Cold blooded

  • Metamorphosis in stages from egg to juvenile

  • Can change color

  • Around 4,500 kinds of crabs

  • 62 kinds of Fiddler Crabs

  • Indigenous to U.S. means can be found here

Body structure
Body Structure

  • 2 main parts

    • Cephalothorax (head and thorax)

    • abdomen

  • Body covered by a shell called the carapace.

  • Attached to the cephalothorax are 2 movable stalks that support the crab’s compound eyes.

  • Eyes can see 360 degrees and can extend upward to see over small obstacles and to retract into a groove for protection.

  • They can see stationary objects that are 65-100 feet away and moving figures that are 330 feet away.

  • 2 pair of small antennae on the head – one for smell and the other for touch.

  • Four pairs of walking legs and 2 pinchers connected to the cephalothorax.

  • Walk sideways.

  • The female has 2 small, equal sized claws, and the male has one large claw up to twice the size of the other claw.

  • Use claws to feed and dig.


  • Semiterrestrial – living part time in water and part time on land

  • Remain out of water by keeping a small amount of seawater in their gills.

  • Must return periodically to the water to renew their water supply.

  • If see bubbles while in the water, the crab is producing carbon dioxide as it breathes and fills its gills with seawater.

  • During high tide, they stay in their burrows and emerge during low tide.

  • Change colors – usually dark in sunlight and paler at night or when cloudy and at times will match color to environment.

  • Male feeds only with the small claw but digs with both.

  • Male uses its large claw to attract a female, discourage rivals, and defend territory.

  • Because the claw is white and reflects sunlight, it can be seen at a great distance.

  • If a large claw, which breaks easily, is lost, a new feeding claw will take its place and the new claw will grow to reach the size of the original large claw.

  • Produces a squeaking sound, much like a cricket, by rubbing the surfaces of its big claw against its thorax.

Feeding behavior
Feeding Behavior

  • Feed mainly at low tide.

  • Known as “deposit feeders,” they roam the flats of much and sand, scooping up sand and soil that contain small particles of food, mainly bacteria and algae.

  • Pushes sand and mud into its mouth with the small, spoon-like feeding claws.

  • Layers of moving mouth parts open and close like elevator doors, and spoon-like hairs separate the tiny pieces of food from the sand and mud.

  • After filtering out the food, it forms the sand and mud into little pellets and deposits them on the ground.

  • They often feed on dead fish and other creatures.

Survival behavior
Survival Behavior

  • Hide among marsh plants and dig burrows for protection.

  • Dig its burrow above the tide line.

  • A burrow can be up to 2 feet deep.

  • Burrow usually houses one crab at a time.

  • To prevent water from entering its burrow, the fiddler lines the burrow with mud and plugs it up using the pellets at the burrow’s mouth.

  • At the burrow’s deepest end, the fiddler digs another few inches, creating a horizontal tunnel.

  • During both high tide and winter hibernation, the crab stays in the tunnel.

Life cycle
Life Cycle

  • Mate in the spring.

  • Male attracts female by waving its large claw or by drumming it against the ground at night.

  • Each species has a specific wave pattern that females can recognize.

  • Reddish, brown eggs that hatch in water.

  • The newly hatched babies are microscopic and undergo a series of molts before becoming pea-sized juveniles.

  • When young, they molt about once every 10 days; as adults, once or twice a year.

  • The life span is around 2 years.

  • After a molt, it has soft shell for about 30 minutes.


  • Feeding

    • Feed once a day at 7:40.

    • Put food in water and on land.

    • Remove old food before adding fresh food.

    • Can also feed small pieces of apple, banana, or lettuce on the sand.

  • Water

    • Change the water once a week.

    • Slowly lift the water bowl, dump the water, rinse the bowl, replace the bowl in the habitat, and refill water.

    • Important not to spill water onto the sand.

  • Move habitat gently.

  • Put plankton in water and on land.

  • What happened when you put food in tank?

  • Do the crabs respond to the food the same way the frogs do?

  • How are the crab’s responses different?

Reading selection
Reading Selection

  • Read

  • Write 2 or 3 things you discovered about how people study dolphins.

  • How is the animal research you are doing similar to the dolphin research being done at the research center?

  • How is it different?

  • How is your animal log similar to the data sheet the research center is using?

  • How is it different?


  • Research other kinds of crabs and create a display.

  • Use a Venn diagram to compare the classroom habitat of the crab with its natural habitat.

  • Feed the crabs a variety of foods to discover which the crabs prefer. Experiment with tuna flakes, shrimp pieces, green vegetables, and fruits.

  • Crustaceans are a popular food source for humans. Research the nutritional value of crustaceans, as well as diverse ethnics dishes that use these animals.