Handbook of Nature-Study · Lesson XCII · Topic 14: Mosquitoes, flies and beetles
92. The Colorado potato-beetle
Goal: Your child can describe the potato-beetle and its larva, tell how it protects itself, and follow its life story on a potato plant.
You'll need
- A potato patch (or eggplant plants) in summer
- A clear jar with a cloth cover and a little soil (optional)
- A hand lens (magnifying glass)
- A nature notebook and a pencil (colored pencils if you have them)
What's in the book
Comstock's story of the potato-beetle as a lesson in warning colors: it plays possum, then gives off a bad-smelling orange liquid, so birds won't eat it. Then Lesson XCII's leading thought, a method that ties it to gardening, and eleven questions on the beetle, its eggs, larva and pupa.
The lesson, step by step
When and where
Late spring through summer, on potato plants, and also on eggplant. Look under the leaves for clusters of orange-yellow eggs, and for plump, reddish, black-spotted larvae chewing the leaves.
Safety first
Potato leaves, stems and green potatoes are poisonous to eat. Comstock asks what happens if you squeeze the beetle: just hold it gently in an open hand, because a light touch is enough for it to show its tricks. Wash hands with soap and water afterward.
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 Colorado potato-beetle is a very important insect, since it affects the price of potatoes each year. It is disagreeable as a food for birds, because of an acrid juice which it secretes. We should learn its life-history and thus be able to deal with it intelligently in preventing its ravages.
The beetle
What is the shape of the potato-beetle? Describe the markings on its head. What color are its eyes? Describe its antennæ.
Why is this insect called the ten-lined potato beetle?
Count the lines on the wing-covers to check.
Playing possum
Take a beetle in your hand. What does it do? Of what advantage is it to the insect to pretend that it is dead?
Why will birds not eat the potato-beetle?
Eggs and larvae
Where does the mother beetle lay her eggs? Are they laid singly or in clusters? What color are the eggs?
Describe the young larva when it first hatches. What color is it at first? Does it change color later? Describe the colors and markings of a full grown larva.
Does it remain in sight while it is feeding? Does it act as if it were afraid of birds?
Put it into words
Ask your child why a bright, easy-to-see insect is not eaten by birds. Then read the leading thought aloud. Gardeners still pick these beetles off by hand into a can of soapy water; your child can help.
Nature notebook
Draw the beetle with its ten stripes, a cluster of eggs on the underside of a leaf, and a larva. Date them, and note which plant they were on.
Tip
Comstock suggests putting other plants in the cage "to prove that these insects will only eat the potato." In fact they also eat eggplant and a few other plants of the potato family, so your child may get a surprise.