LEAF-ROLLERS
“Many of the moths bearing the name of pyralis have a curious habit in
their larva state, of rolling up the leaves of trees, or of folding
them lengthwise, or of uniting several in the form of a sheath by means
of silk threads, so as to make a shelter in which they may nibble away
in safety at the interior of their green abode. For this reason they
are called leaf-rollers. The one best known, on account of the damage
it does, is the grapevine-pyralis.
“It is a small moth with yellow wings having the metallic sheen of
copper and crossed by brown stripes. Its larva is greenish, bristling
with short hairs and having a head of a dark lustrous green color. In
August the moth lays its eggs on the vine leaves in little slabs of
twenty at most. Hatching takes place in September. At this advanced
season of the year caterpillars do not eat; they suspend themselves by
a thread and wait for the wind to drive them against the vine or one of
its supports. As soon as they get a foothold on the desired object they
take refuge in cracks in the bark and fissures in the wood, and there
they lie torpid through the winter. At the reawakening of vegetable
life and the first pushing forth of the new vine shoots they leave
their winter quarters, invade the vines, and entwine with silk threads
the young grape clusters and the tender leaves, after which they feed
upon them with an appetite sharpened by a fast of five or six months.
With such ravenous eaters devastation proceeds apace, and in a few
weeks, if the worms are numerous, the most flourishing vine is reduced
to a pitiful condition and all hope of a harvest is abandoned. The
ravages wrought by this moth between 1835 and 1840 in the vineyards of
Bourgogne will long be remembered. Over immense tracts of land, when
vintage-time came, there was not a single bunch of grapes to go into
the basket. The greedy caterpillars ruined the country.”
“Didn’t the people try to get rid of the creatures?” asked Louis.
“They tried various methods, but with little success until finally one
proved effective, and that the simplest and cheapest of all. Let us
note by the way, my little friends, what an advantage it is to be
acquainted with the habits of an insect that does us harm. If this
moth’s peculiarities had not been studied, if it had not been known
that its larvæ hide themselves in the fissures of the vines and the
trellises, there to lie torpid all winter, our vineyards might still be
suffering from this terrible enemy. This fact being known, the remedy
was not far to seek.
“It is this: in winter the vines and trellises are scalded with boiling
water, the water being heated over a fire in the middle of the
vineyard. “With a coffee-pot about a liter of hot water is poured on
each vine so as to reach all the parts where worms may be lurking.
Protected by its tough bark, the vine itself does not suffer from this
scalding bath, while the caterpillars are completely destroyed. By this
method the vineyards of Bourgogne were so entirely rid of the dreaded
moth that no further ravages of any account have been reported.”
“Couldn’t the moths come back again some time, as many as ever?” asked
Jules.
“That is hardly possible if at their first appearance the coffee-pot of
hot water is brought into play.
“The other leaf-rolling moths of this family are of less importance.
The leaf-roller of the plum-tree lives first on the blossoms of the
tree; later it makes a roll of leaves and lines it with silk. The moth
has a large white spot at the tip of each fore wing.
“The cherry-tree leaf-roller has about the same habits. Its moth is
recognized by two wide oblique stripes of the color of rust on its fore
wings. On the pear-tree lives a leaf-roller with a triangular white
spot in the middle of each fore wing.”
“I don’t remember ever having seen the moths you are telling us about,”
said Jules.
“They are too small to be noticed by any one who is not on the lookout
for them.”
“I have often seen the nests of leaf-rolling caterpillars on
fruit-trees and bushes and all sorts of plants. There are leaves folded
lengthwise so that the edges join and make a sort of tunnel; others are
in twos or threes or more; and there are some fastened together in a
big bunch, all twisted and ragged, with silk threads holding them
together. On opening these nests of leaves and silk I have sometimes
found a caterpillar and sometimes a spider.”
“Various spiders with too little silk to spin a large web for catching
flies make an ambush by bringing the edges of two or three adjacent
leaves together. Like the leaf-rolling caterpillars they use silk
threads to hold the pieces of their abode in place, but their ultimate
object is quite different. The rollers bring the leaves together so as
to nibble them in peace, safely hidden away in the shelter thus formed;
the spiders bring them together to make a simple abode for themselves
and an ambush from which they can pounce upon such insects as come
within their reach.”
“The spiders that make a nest of leaves joined together do not harm
trees?”
“I should rather say they are helpful to trees. They are vigilant
guardians, always on the watch for flies, gnats, little moths, and
other ravagers that would come and infest the trees with their eggs.”