Silk worm larva
The silkworm is the only domesticated insect. Over thousands of years
of selective breeding the adult
form has lost the ability to fly and would probably not survive more than a few generations in the wild.
This sets it apart from the honeybee which, though often raised in captivity, is no different from
wild bees and readily forms wild colonies when queens manage to escape. Though silkworms fed exclusively
on mulberry in the wild, there are artificial substitutes which are sometimes included with eductational
Silk worms tend to move upward as they feed. This causes problems when silkworms
commercially since they tend to concentrate at the top end of their containers. This is solved by keeping
them in containers which are balanced on rotating mounts so that when too many larva migrate to
the top the now top heavy container will flip over, thus keeping the larva more evenly distributed.
The silk which makes up the cocoon is a continuos thread which may be up to a mile long! Because it is
so thin, 20 strands must be spun together to make one thread. The strand is
held together with a gummy substance, so attempting to unravel it would break it. The emergence of the
moth also breaks the strand. Thus, the only way to get a usable strand is to dissolve the gum by boiling
the cocoon in water with the pupa still inside. Only the best cocoons are allowed to develop normally,
thus ensuring the quality of the next generation. Because each female lays thousands of eggs, most of the
cocoons can be harvested while maintaining sufficient breeding stock. So even though many of the eggs
will hatch and grow into mature larva, very few survive to adulthood.