Well, scream if you want to; that won"t do any harm.
It _isn"t_ pretty! but we shall like to look at it. You see it is a larva and a big one, dark gray in color and with a thick leathery skin.
Mollie says it reminds her a little of the larva of the May fly; that is, in shape.
Let us look at a picture of the May-fly larva.
You see it has a head, a thorax to which is attached the six legs and the rudimentary wings, and an abdomen, all distinctly separated from each other.
[Ill.u.s.tration]
The dobson has a head, but no thorax.
The body behind the head is divided into segments that all look very much alike, and there is a pair of legs attached to each of the first three segments.
The dobson eats other larvae that it chews up with its strong jaws.
It lives almost three years in the larval state, so you see it has plenty of time in which to grow. Of course it moults. It is usually to be found under stones in swift, running water. Those two pairs of hooks at the tip of its body are its anchors.
It clasps them about a bit of stone or a stick that is firmly lodged, and then it can bid defiance to the swirling stream.
Ned wonders why it is always found hiding under stones.
Listen to John, he says fishes are very fond of dobsons, and that is why they hide away.
Fishermen hunt the dobsons for bait; so you see they have a hard time in spite of their large size and their strong jaws.
When they have lived nearly three years in the water they crawl out on the bank and hollow out a place under a stone.
Here they lie, apparently dead, but they are not dead.
They are undergoing a wonderful transformation.
It takes about a month for this transformation, or _metamorphosis_, as it is called, to be completed.
All of our other insect friends have changed gradually from larval to adult form. At each moult they became a little more like their parents, and finally at the last moult, without any resting period, out sprang the perfect insect.
Not so the dobson. It goes into its hole in the bank a larva, almost exactly like the larva that hatched from the egg, only, of course, it is larger. There is no hint of wings. It has no separate thorax and abdomen. Could we see under the bank where it has crept, to undergo its great metamorphosis, we should find, not a larva, but a strange-looking, motionless object.
[Ill.u.s.tration]
Here is the picture of one. See its little wing pads. And now it has a thorax and an abdomen.
It seems to have changed and been turned to some hard substance.
In this state it is called the _pupa_, which means doll. Is it not a cunning insect doll? But it is not really a doll. Although so still and apparently lifeless, yet it lives.
Some day it will burst its pupa sh.e.l.l and pull itself out--not a larva now, not a pupa, but a strong-winged insect.
In its adult form, it is known as the horned corydalus.
There! I thought John was saving one for us. He had it in a box in his pocket. Now see what a--a--what shall I say? A beauty? or a monster?
That is just as you feel about it.
It certainly is an alarming-looking insect.
This one is a male, as we can tell by the long, curved jaws that look very dangerous; but in this instance the creature"s appearance is worse than its bite, and the real biter is the female whose jaws are smaller but very useful in nipping tormentors or biting prey.
Now here she is--a fit mate for her formidable-looking companion.
[Ill.u.s.tration: MALE CORYDALUS.]
[Ill.u.s.tration: FEMALE CORYDALUS.]
John, you were fortunate in your hunting.
In spite of its terrifying appearance, see what wonderful wings the corydalus has.
See! John has spread out the wings of the female.
They are indeed beautiful.
May cannot understand how those great wings came out of those little wing pads.
When the wings were first pulled out of the wing pads they were small, but they rapidly expanded and became thin and broad and long as the air touched them.
You will understand that better after a while.
The corydalus differs from all the other insects we have studied, in its metamorphosis.
It begins life far more unlike its parents than the other insects we have been looking at, for they had the thorax and abdomen distinct from the beginning. Instead of changing gradually and remaining active all the time up to the final metamorphosis, our corydalus goes into the pupa state, and in that motionless condition transforms to the perfect insect.
This is called a complete metamorphosis.
When the change is gradual, without any pupa form, any stopping place as it were, the change is said to be an incomplete metamorphosis.
Yes, the metamorphosis of the gra.s.shoppers is incomplete, and of the katydids and the crickets and all the other insects we have studied until we came to the dobson.
Another name for the larva of insects that undergo an incomplete metamorphosis is _nymph_. Some books speak of the nymph of the gra.s.shopper, and never of the larva of the gra.s.shopper. Such books use the word _larva_ only in speaking of the young of insects that undergo a complete metamorphosis.
Yes, Ned, they would speak of the nymph of the dragon fly, and the nymph of the May fly and the nymph of the cricket and the katydid, but they would speak of the larva of the corydalus.
Egg, nymph, adult,--those are the stages of insects that have an incomplete metamorphosis.
Egg, larva, pupa, adult,--those are the stages of insects that have a complete metamorphosis.
No, it is not wrong to say larva instead of nymph. I only want you to know how the word nymph is used, so that when you see it in reading about insects you will know what it means.