Yes, it is the plural form of the word. When we speak of only one we say
"larva"; when we speak of more than one, instead of saying "larvas," we
say "larvæ."
The dragon fly larvæ are terrible gluttons, and hidden under the mask
are strong jaws for chewing up their prey.
Their legs are quite large and strong, too, for they crawl about the
bottom of the pond or up the stalks of the plants.
They do not move about very fast, but they do shoot out that under lip
very, very, _very_ fast indeed, so good-by to any little live thing in
the pond that comes within reach of it.
The dragon fly larvæ do not all look alike. They are different in the
different species of dragon flies, and, like the rest of us, they change
as they grow older.
Yes, May, you can keep the dragon fly larvæ until they change into
dragon flies.
You must supply them with fresh water and with enough to eat.
And you must put a net over the bowl or aquarium in which you keep them,
otherwise as soon as they are able they will fly away.
How can they fly without wings?
Oh, but they are going to have wings. You know they are young dragon
flies in spite of their strange appearance.
Be sure and feed them enough, or else they will eat each other, and that
would be a pity; and be sure there are some water plants for them to
hide under and crawl upon.
You can give them a little fresh fish or a tiny bit of very fresh meat,
though they like best the living things they find in the bottom of the
pond.
[Illustration]
When the dragon fly larva first hatches it is very small and its legs
are rather long and spidery, but it eats and eats and eats,--my, how it
eats!
And it grows and grows, and one day it finds its skin too tight.
A tight skin must be rather uncomfortable.
But the larva does not care much for its skin.
It merely splits it open down the back and pulls itself out.
Perhaps you think it must be yet more uncomfortable to be without a
skin.
But it is not without a skin. It is covered by a new and soft one that
soon hardens, and that is larger than the old one.
It wriggles out of its old skin as though it were an old coat, and
leaves it clinging to the weeds in the pond.
Sometime you may find these cast-off dragon fly overcoats.
After it has shed its skin the dragon fly continues to grow. It keeps on
growing until it has outgrown its new skin.
Then what do you think it does?
Yes, Charlie, that is right, it sheds this skin too.
[Illustration]
When it sheds its skin we say it moults.
It moults several times, and at last little short wings appear. At first
it has no wings at all, you know.
Amy wonders how the larva breathes under water.
Ah, Master Ned, you are laughing too soon. You think insects do not have
to breathe, but you are very much mistaken, sir.
Insects do have to breathe.
They would die if they could get no air to breathe.
Some of the dragon fly larvæ have an odd arrangement for breathing under
water. They have a sort of syringe in the end of the body, and there are
breathing pores or gills in the syringe.
The water goes in and out of this syringe, and the larva breathes as the
fish does, by means of its gills.
Yes, May, its gills are in its syringe, which seems very odd,--you see
the dragon fly larva breathes at its tail end instead of at its head
end.
Mollie thinks it is an upside-down, inside-out sort of a creature
anyway. But it knows what it is about.
Ned wants to know how it can get any air to breathe when it lives under
water.
The truth is, there is always air mixed in with water, and it is this
air the larva breathes when the water goes in and out of the syringe.
It uses the syringe for another purpose too. When it pleases it can
shoot out the water with great force, and thus propel itself quite a
distance.
By means of the syringe it can leap through the water faster than it can
move by its slow-going legs.
Mollie wants to know if we can see the syringe.
No, it is inside the body.
But there is a kind of dragon fly that has a pair of gills outside, at
the end of the abdomen, instead of the syringe inside.
The best I can do is to show you a picture of one. Some day we may find
it in the pond.
[Illustration]
Those two feather-like parts at the tail end are gills.
Yes, John, it can propel itself through the water by rowing, as it were,
with these gills.
There are some species of dragon fly larvæ that swim by moving the tip
of the abdomen from side to side, as a fish moves its body when it
swims.
But now let us return to our funny larva that lives at the bottom of the
pond. It stays down there, eating and growing and moulting, for nine or
ten months or even longer; then something very wonderful happens.
It suddenly feels a great desire to get up to the top of the pond.
[Illustration]
It climbs up a weed or a stick until it is clear out of the water.
Then its skin splits down the back for the last time, and out there
pulls itself, not a larva, but a weak-looking dragon fly, with soft and
flabby little wings.
Now is its hour of danger, and now is the time for such birds as like
the taste of young dragon flies to help themselves.
Catbirds seem to have a special fondness for these helpless insects, and
have been known to eat them before the flabby little wings had grown
stiff.
If the birds do not find the newly emerged dragon fly, it remains
motionless an hour or so, but it does not remain unchanged.
Its wings stretch out and harden.
Bright metallic colors begin to play over them and over its body; and
all at once--off it darts, away and away, glittering in the sunshine, a
swift, beautiful winged creature.
Towards the end of summer you will often see dragon flies darting about
in every direction.
They seem to come in swarms and I think they usually come where there
are ponds or marshes, for in such places there are many gnats and
mosquitoes.
Mollie wants to know why it would not be a good plan for people who live
where there are many mosquitoes to raise dragon flies?
That is a very sensible idea, Mollie, and it has been tried.
Yes, indeed; some men once collected dragon fly larvæ, and took care of
them until they changed into dragon flies.
Then what do you think happened?
As soon as they got their wings, away went those dragon flies,--away
and away, without stopping to catch a single mosquito for the men who
had taken the trouble to raise them.
The dragon flies will not stay at home.
They fly so fast and so far there is no use raising them.
They are among the swiftest and strongest of insects.
How do the larvæ get in the ponds? Frank is asking.