Handbook of Nature-Study · Lesson CVIII · Topic 17: Snail, earthworm and crayfish
108. The crayfish
Goal: Your child can describe the crayfish's claws, legs, eyes and tail, and explain how it walks, swims backward and hides.
You'll need
- A shallow, clear stream with stones (or a pond)
- A dip-net or a large plastic cup
- A white tub or dish pan of stream water with some gravel
- Rubber boots or old sneakers
- A nature notebook and a pencil (colored pencils if you have them)
What's in the book
Comstock's story of the crayfish, so "rich in organs": its great nippers, walking legs, jaw-feet, swimmerets and fan-shaped tail, and how it walks forward and darts backward. Then Lesson CVIII's leading thought, method and seventeen questions.
The lesson, step by step
When and where
Late spring to early fall, in shallow streams with stones. Turn over stones slowly and watch the water just downstream. In wet meadows you may find their mud chimneys.
Safety first
Water safety: an adult stays within arm's reach of young children at the water's edge. Keep back from steep or slippery banks, and wash hands after handling pond water, mud or water creatures.
Crayfish pinch. Scoop one up with the net or cup and look at it in the tub; if an adult picks one up, it is by the back just behind the big claws. Look for a little while, then let it go in the same stream. Never move crayfish to a different pond or stream.
Keep the big idea in mind
Comstock's "leading thought" is the one idea the lesson is meant to lead to. Read it to yourself now, and save it to share at the end, after your child has looked and answered:
The crayfish, or crawfish, as it is sometimes called, has one pair of legs developed into great pincers for seizing and tearing its food and for defending itself from enemies. It can live in mud or water. It belongs to the same animal group as do the insects, and it is a near cousin of the lobster.
Claws and legs
What is there peculiar about the crayfish which makes it difficult to pick it up?
How many legs, in all, has the crayfish? What are the short legs near the mouth used for? What are the great nippers used for? How many legs does the crayfish use when walking?
Eyes and feelers
Look carefully at the eyes. Describe how they are set. Can they be pushed out or pulled in? Can they be moved in all directions? Of what advantage is this to the crayfish?
How many antennæ has the crayfish? Describe the long ones and tell how they are used.
The tail
Watch it dart away in the tub.
How does the crayfish swim? With what does it make the stroke?
Of how many pieces is the tail made? Make a sketch of it.
Hiding
Add a few stones to the tub and watch.
Where do they like to hide? Do they go headfirst into their hiding place, or do they back in? Do they stand ready to defend their retreat?
When you look down into the brook, are the crayfishes usually seen until they move? Why is this?
Then let it go and read the leading thought aloud.
Nature notebook
Draw the crayfish from above, label the nippers, walking legs, eyes on stalks, long antennæ and the fan-shaped tail, and count its legs.
Afterwards
Comstock asks: "If the crayfish loses one of its legs or antennæ, does it grow out again? How does the crayfish grow?" Look along the stream for a cast-off crayfish shell, left when it molted.