Nature and Art, June 1, 1866.] 
THE AILANTHUS SILKWORM. 
15 
The larv® or caterpillars, -when just hatched, are dusky 
black ; they moult several times. The first moult takes place 
from seven to ten days after they are hatched ; they then 
appear of a light yellow. This colour they retain for five 
or six days, when their second moult takes place, and then 
their skin secretes a peculiar yellow powder looking' some- 
what like the down on a plum. This repels water, and it is 
to it that they are apparently indebted for their power of 
resisting- rain. The third moult takes place in about six 
days after the second, when the larvse become of a greyish 
blue, and are so very much covered with white powder as to 
look as if dusted over with pounded sugar. 
It requires hut another interval of six days to bring on 
the final moult, after which the worms eat enormously. 
Dr. Wallace states that they grow so rapidly as to increase 
in weight as much as six-fold in nine days. Their appetite 
is so voracious that it is quite common at this period of 
their growth to see a tree covered with foliage one day and 
quite bare the next ; while the hungry larvae are gnawing 
down the tender ends of the leaf-stalks, or are wandering off 
to other trees in quest of food. It is, he says, often a start- 
ling surprise to see bare leaf-stalks, where luxuriant foliage 
existed twenty-four hours previously. During this final 
period of their caterpillar or larval state, the worms assume 
their most beautiful aspect. When full grown they are 
magnificent in size, and the greater part of the body is of 
a most delicate green colour, covered with tubercles tipped 
with an exquisite marine blue tint, while the head and tail 
are tinged with a brilliant golden yellow. The food taken 
during the last stage supplies the nourishment from which 
the silk is produced. In the interior of the body of the worm 
are two very long convoluted tubes. These, shortly before 
the cocoon is spun, become filled with the liquid which is 
drawn out in the silken fibres of which the cocoon is con- 
stituted. 
Although known as the ailanthus worm, from feeding on 
the shrub of that name, there are many other plants on 
which the Bombyx Cynthia will thrive ; the ailanthus, how- 
ever, appears to be its proper and favourite food. 
The common laburnum is eaten greedily, and the castor- 
oil plant is also taken readily. The changes which are 
effected in the insect by an alteration of diet remain to be 
seen. Many entomologists imagine that the castor-oil 
worm (Bombyx Ricinus) and the ailanthus worm are varieties 
of the same animal — the differences between them being 
caused by alteration of food. If so, it is a remarkable 
instance of an extreme variation, not only of form but of 
habit, resulting from external circumstances ; for the castor- 
oil worm rears several broods in the year, the ailanthus only 
producing one or two. 
The spinning of the cocoon offers one of those remarkable 
examples of instinct that are apparently so inexplicable. 
The worm feeds on trees whose leaves are deciduous, and 
its cocoon is formed by bending a few leaflets together and 
spinning the mass of silk in the midst. In the natural course 
of events the leaves would fall in the autumn ; and the 
cocoon would thus become liable to injury from lying on the 
ground. But this evil is entirely obviated ; for, with an 
instinct that looks almost like foreknowledge, the worm, 
before spinning its cocoon, passes along the lengthened foot- 
stalk of the leaf, and spins an excessively strong band of 
fibres, connecting it firmly to the stem of the plant. These 
fibres are continued round the footstalk down to the leaf 
itself ; so that even if the stalk of the leaf be broken from 
the branch, or fractured in any part of its length, the cocoon 
cannot drop, being securely held by the strong silken fibres 
that connect it to the parent stem. 
Having thus secured its foundation, the worm pulls several 
of the leaflets together, or curls inwards the edges of one of 
sufficient size, and proceeds next to spin the silken covering 
with which it is concealed from prying eyes during its 
marvellous change from caterpillar to perfect insect. As is the 
case in ordinary silkworms, the outside of the cocoon is first 
formed, the worm working from without inwards, and arrang- 
ing the silk in successive layers one within the other. This 
operation lasts for a considerable time, and the worm can be 
heard moving in its narrow cell for many days. There is 
one very important difference between the cocoons of the 
ailanthus and those of the mulberry worms, which threat- 
ened to offer almost insuperable difficulties to the rrtilization 
of the produce of the former. The layers of silk, as they 
are spun, are agglutinated by an exceedingly tenacious gum, 
which connects the threads so firmly together, that the 
cocoons cannot be reeled off in the usual manner. 
Hitherto they have been separated by carding. From 
experiments which have been recently made with the object 
of dissolving the gum, there appears but little doubt that 
eventually the silk will be reeled off the cocoons in one con- 
tinuous fibre. In fact, this is now done by the Chinese. 
It must not be imagined that ailanthi-culture is still 
entirely a mere experiment. The worm is largely cultivated 
in the north of China. Ailanthus silk fabrics are sold 
as regular articles of commerce in France ; and, though 
not possessing the distinguishing gloss of the ordinary 
silk, are remarkable for their beautiful appearance, 
and, above all, for their almost everlasting duration. It 
is said that in China a dress of this material descends as 
an heirloom for generations. Nor is the possibility of 
the successful culture of the worm in England a mere 
uncertainty. Dr. Wallace has planted many thousand 
ailanthus trees along the Essex railway banks ; and these, 
last season, were all utilized. In fact, the introduction of 
this useful insect offers good prospect of establishing a 
new and profitable national industry, one which can be 
pursued advantageously in , the most barren and sterile 
places ; and which offers a lucrative employment to those 
persons who are by age or sex incapacitated for severer 
exertions. 
For the efforts of Lady Dorothy Nevill, Lady Mary 
Thompson, and Dr. Wallace, we can desire no better reward 
than that such a result should crown their exertions. 
[As many of our readers may be desirous of propagating 
this handsome and interesting insect, some remarks on the 
cultivation of the shrub producing the leaves on which it 
feeds may not prove unacceptable; and as the subject has 
been so ably treated by M. Guerin-Meneviile in his treatise 
on the “ Ailanthus,” we cannot do better than give an 
extract from Lady Dorothy Nevill’s translation of that 
work. — E d.] 
“ The seeds may be sown from the month of February 
till May, broadcast or in rows, and ought to be covered 
with about half an inch of earth, and they will appear 
from three weeks to a month after they are sown. With 
the exception of a few cereal grains, there are hardly any 
other shrubs where the seed germinatos so quickly, and it 
is not uncommon to see some of the shoots from these 
seeds thirty and fifty inches high the first year. Numbers 
of ailanthus trees have been planted on the Apennines, 
because they resist the bite of animals, and no ground game 
will touch them on account of the smell they exude when a 
leaf is gathered or a branch broken off. Those trees destined 
for the reception of the worms ought to be planted about a 
yard from each other, the chief stem cut down every year, 
so that the young shoots spring up and afford young tender 
leaves for the worms ; and by planting them not too great a 
distance one from another, the shoots join each other, and 
thus enable the worms to go from one plant to another. 
As I mentioned before, this tree may be multiplied by its 
roots, which may be cut off and planted, as we do potatoes. 
Where the plants are yearly cut down, they naturally will 
not flower or seed. Experience has taught me that if trees 
are planted from twelve to fifteen feet high, they may be cut 
down immediately to within two or three feet of the soil, 
so that they will immediately throw out fresh shoots. This 
tree is so hardy and so easy to propagate that in a planta- 
tion of 15,000 to 20,000 plants made in France not one 
died. In England it is equally hardy. I planted three 
dozen standard plants on a sloping bank, exposed to the 
sun ; the heads were cut off, and the leaves began to sprout 
about the middle of May.” 
