leukocyte 201Thefirst requirement of silk-making is the gathering
of moth cocoons for processing into long threads for
weaving the fabric. The earliest source of cocoons was
almost certainly local wild moth populations. Silk-makers
must have soon learned which moth species produced the
best and most easily processed silk. The next step may
have been some form of silk-moth domestication. In its
simplest form, this might have meant securing eggs from
fertile females and raising the caterpillars in protective
custody on appropriate food plants, either living plants or
fresh-cut foliage, in much the way amateur silk-moth
enthusiasts raise them today. In time, however, more
sophisticated, assembly-line-style rearing techniques
were developed in which caterpillars were reared en
masse indoors in containers.
Only one species of silk moth, the mulberry silkworm
moth (Bombyx mori), a member of the family Bombycidae,
has been completely domesticated. This species appears
to have been selectively bred for rearing the caterpillars
on flat screen trays stacked in tiers, an extremely space-
efficient means of production. Over time, silk producers
developed caterpillars lacking the velcrolike ends of the
abdominal legs (called “prolegs,” as they are not true
legs), so that they did not crawl off the breeding trays, but
stayed there feeding as long as they were supplied with
leaves. A singular advantage to this species is that the
cocoon, after the gummy sericin is boiled away, unravels
inone long, unbroken thread of fibrin, an extremely strong
and supple protein. The cocoons of saturniid silk moths
cannot be so easily untangled, nor is the resulting silk of
such refined quality. Saturniid sericulture utilizes cocoons
of several Asian species of the genus Antheraea,which
also contains the familiar North American polyphemus
moth (Antheraea polyphemus).In China, the coarse silk
from Antheraeaand a few other genera has long been
used for everyday garments, including sturdy work
clothes.
In North America, early colonial settlements in the
Carolinas and Georgia produced silk for local use using
the mulberry silkworm. Later, in the middle 19th century,
commercial silk production was promoted in Europe and
North America as a viable industry, but startups in the Unit-
ed States, mostly along the east and west coasts, proved
too costly against foreign competition, bringing American
sericulture to an early end. Its legacy remains, however, in
the form of one lovely moth and its host plant, and in the
form of an unlovely moth that haunts the Northeast to this
day. A major silk promoter, the Frenchman Léopold Trou-
velot, imported both moths in the 1860s.
The good moth is the ailanthus silk moth (Samia cyn-
thia), which feeds in the wild only on the tree imported as
food for its caterpillars, the tree-of-heaven (Ailanthus
altissima), also known as “stink-tree” for the musty smell of
the male flowers. The moth and the tree grow in many
cities, mostly along the east coast, with scattered occur-
rences as distant as Pittsburgh and St. Louis.
Trouvelot’sother introduction is the notorious gypsy
moth (Lymantra dispar). Having escaped from Trouvelot’s
unsuccessful crossbreeding experiments with the mulberry
silk moth (Bombyx mori), the gypsy moth invaded the local
New England forests and spread, becoming perhaps the
most devastating forest insect pest in the Northeast, with
periodic outbreaks defoliating millions of acres of trees.
Most trees recover, and the gypsy moth populations plum-
met after one to three years, so there is no lasting damage.
The ailanthus silk moth is well behaved by comparison,
never spreading from cities into the countryside, nor attack-
ing trees other than its natural host. Though tree-of-heaven
is widespread in disturbed portions of rural areas (along
highways and power-line cuts, for example), the moth is
never found in these wilder places, only in sooty railroad
yards, unkempt used car lots and junk yards, and similar
sites. Probably the caterpillars are so vulnerable to our
Banded-purple butterflies gathering at a mud puddle in the native predators and parasites that inevitably all are killed
Adirondacks in order to siphon up sodium ions that are
needed for metabolism.(Courtesy of Tim McCabe) (continues)