The Life Cycle of the Silkworm
Although the life of a silkworm is only between six to eight weeks long, it's a dramatic six to eight weeks, involving a metamorphosis as strange as any Transformers movie and a truly bizarre ending. Before we get to that though, we need to start at the very beginning of a silkworm's life.
Eggs
The egg, as you'd probably guess, is the first stage. A female silkworm moth will lay about three-hundred and fifty of them, with each egg being about 1mm in diameter. In seasonal climates, a female moth will tend to lay eggs toward the end of summer, with the eggs remaining dormant over the winter months, hatching once the temperature rises in springtime. Although this normally happens only once a year (when the leaves of the mulberry tree begin to grow — the worms' favorite food), with human intervention and the supply of specially formulated nutrients, the process is now a year-round activity (with eggs hatching at least three times annually). Incidentally, if you are breeding silkworms in captivity, silkworm eggs can be stored in a fridge for up to three months to delay hatching until you're ready to start raising them.
Larvae
When the eggs hatch, a baby silkworm larva will emerge. No more than an eighth of an inch long and covered in hair, it will immediately start searching for mulberry leaves (or whatever food source is available if it's being bred in captivity). In this larva stage, the caterpillar will grow rapidly, passing through four distinct molts, each time shedding its old skin and growing a new larger one. Prior to its first molt, the head of the caterpillar will turn a shade darker than its body, after which it will shed its hairy skin, replacing it with a smooth white one with a tiny horn at the back of its body — a look that the caterpillar will keep until it's ready to cocoon itself. These stages between molts are referred to as 'instars' and in total will last somewhere between twenty-four and thirty-three days. Toward the end of this larva stage, the silkworm will start to feel the need to cocoon and begin to look noticeably different — appearing translucent and slightly yellowish in color. It will then produce a thin, watery fluid that it uses to wash out its system before getting ready to wrap itself in silk.
Cocoon
The cocoon is the real business end of a silkworm's life. From its glands, the worm initially excretes a small droplet of silk that it uses to anchor itself. It then starts producing a single lengthy filament of silk (that can be up to a mile long) which it wraps around its body. The process takes about two days for the silkworm to complete and will leave it entirely encapsulated in an ovate silk cocoon about the size of a cotton ball. Now, assuming the silkworm is not being bred for silk, the worm will remain in this cocoon while it goes through its final and most dramatic change.
Adult moth
After a one or two-week period, the cocoon will begin to rupture as a newly-formed silk moth slowly begins to emerge. Once out of its cocoon, the moth will again excrete a watery fluid to clean out its system, before revealing itself in all its glory. The one-time plump little caterpillar has now transformed into a large moth with a wingspan of two inches, and bristles all over its body (Michael Bay would be proud).
The twist in the tale
Unfortunately for the silk moth, centuries of human breeding and domestication have left the moth unable to fly — its wings are now completely useless. Although some males can nearly fly, they can only do so if you drop them in mid-air, after which they will flutter around uncontrollably until they hit the ground. Unable to get airborne, silk moths spend most of their time walking around, trying to have sex — and considering that they don't have mouths, they can't even buy each other dinner beforehand. It's a bizarre finale to the silkworm's life — and a brief one at that. Unable to eat or drink, the moths survive as long as they can on stored fat supplies (up to ten or fifteen days in most cases).
When it comes to telling male and female silk moths apart, females have much larger abdomens and are generally less active than males. Either way, both sexes start looking for a mate almost as soon as they leave their cocoon, and after mating, the female will lay approximately three-hundred and fifty eggs then die. Although the male will continue looking for another mate, it needs to be quick about it as it tends to die only a few days after the female.
And so, with the new eggs laid and the adult moths dead, the silkworm's circle of life is complete. It may not be the longest or most fulfilling of lives, but the silk that the worms produce in the process is among the most prized materials on the planet. So next time you buy a silk shirt, just remember what the flightless, mouthless silk moth had to go through in order to make you look fabulous.
Hatch your own silkworms
Watching this cycle unfold is half science lesson, half magic trick — and silkworms happen to be one of the most nutritious feeders you can offer a reptile. Start from silkworm eggs with our powdered silkworm chow, or skip ahead with live silkworms — all backed by our Live Arrival Guarantee.