The Silkmoth

By Connie Gould

Introduction

The silkmoth is classified under the phylum Arthropoda, and there are two distinct types: the domesticated silkmoth (Bombyx mori) and the wild silkmoth (Bombyx mandarina). The wild silkmoth originated in Asia, in areas such as northern India, China, Korea, Japan, and eastern Russia. It is thought that the domesticated silkmoth came into existence over 5,000 years ago when the Chinese began practicing sericulture (silk farming, or the raising of silkworms to make silk). As a result of domestication, the domesticated silkworm (larva form of silkmoth) cannot reproduce without the assistance of humans. However, upon completing the cocoon stage of developing and become silkmoths, silkworms have the capability of reproducing naturally (reproduction amongst the species can only be done in adult form). There have also been cases of wild and domesticated silkmoths reproducing and forming hybrids. The silkworm can grow up to three inches in length.

Anatomy

In larva (or silkworm) form, the silkmoth has a worm-like appearance with a short anal horn, and it has three distinct body parts: the head, the thorax, and the abdomen. The silkworm has three pairs of short, jointed legs, with a claw at each tip. These legs are found on the three body segments behind the head. There are also five pairs of prolegs that end in a series of hooks called crockets, which are located at the rear end and on the abdomen. The purpose of these legs is to help the silkworm with climbing and holding on to plants. After the silkworm goes through the cocoon stage and becomes a silkmoth (which I will explain in more detail in the next section), it has creamy white wings with brown patterns; the wingspan is about 50mm. Their bodies also become very hairy. Male silkmoths tend to be smaller, but more active than their female counterparts, who are larger, but less active.

Form and Function

Silkmoth eggs take about fourteen days to hatch, and after hatching, they go through three main stages of life: larva, pupa, and adult. During their larva stage of life, silkmoths go through four molts, the process by which old skin is shedded off and replaced with a new layer. The preferred diet of the silkmoth, in both larvae and adult form, are the leaves of the white mulberry tree (Morus alba), although they will readily eat any type of mulberry leaf. Silkworms produce silk by secreting thread from small holes in their jaws; the entire process takes only 72 hours. The pupa stage of the development of a silkmoth occurs when it reaches about one month of age; when they are ready to start spinning the cocoon they will often stop eating and will turn a yellowish colour. The silk used to produce the cocoon is actually hardened silkworm saliva that is discharged through the organism’s mouth. All it takes is a single strand of this silk from the silkworm’s mouth to forms its cocoon; the total length of the strand of silk used to form the cocoon can be as long as a mile. They then spend three weeks in the cocoon, shedding their skin and developing into a moth. The fully developed silkmoth then emerges by secreting a special type of saliva that dissolve the cocoon. The silkmoth will frequently urinate a reddish-brown fluid right after emerging from its cocoon, because it is naturally going to want to “use the bathroom” after being stuck in a cocoon for three weeks. Silkmoths reproduce sexually; by attaching together at their abdomens. The male uses short appendages on his anus to hold on to the female. During this process, a sac called the “spermatophore” is passed through the male moth’s reproductive organs. This sac contains sperm and nutrients for the embryo. The female silkmoth then stores the sac in the bursa copulatrix. The female silkmoth also has eggs inside her body, and shortly after the sperm from the male’s sac fertilizes the eggs, she will lay them. The female silkmoth can lay anywhere between 200 and 500 eggs, which will hatch into silkworms and carry on the lifecycle. Unfortunately for the silkmoth, it usually dies only a few days after mating and laying its eggs.

Impact on the World/Humanity

Silkmoths and their larva form, the silkworm, have had a profound impact on humanity for thousands of years. Sericulture (silk farming) began in China over 5,000 years ago. The Chinese managed to keep this a secret from much of the rest of the world, but eventually the cat was let out of the bag, and silk farming spread to Europe and other parts of Asia. The silk that was produced by silkworms generated significant money in old societies through trade, and continues even today to be of economic value in many Asian countries.

Journal Article Review

Silkworms are the larva of the silkmoth, and they are native to Asia. Silkworms are crucial in sustaining the silk industry worldwide. Within 28-30 days after hatching from their eggs, they begin to spin a cocoon, which they remain in for 2-3 weeks. The silkworm is a very gentle creature, and will not bite, but needs to be handled with care, as they are very susceptible to bruising. They go through four primary stages of development: egg, larva, pupa, adult. The cocoon they spin about a month after they hatch is what they develop from a larva to an adult in. Today, silkworms are domesticated, and live only in captivity, although they have close ancestors still in the wild. For mating, the female silkmoth releases pheromones, and the male silkmoth detects these chemicals, sometimes from long distances, so the male knows where to find the female. Although it is best to feed silkworms regularly, they are able to go without food for a week. There ideal living temperature is anywhere between 78°F and 88°F, although humidity should be kept to a minimum.

Videos

http://www.silkwormshop.com/index.html

http://www.youtube.com/watch?v=ZTsCwFzC4o8

http://www.youtube.com/watch?v=ChBpihQRlaU&feature=related

Bibliography

· Bombyx Mori – Wikipedia, the Free Encyclopedia (n.d.) Wikipedia, the free encyclopedia. Retrieved October 12, 2010, from http://en.wikipedia.org/wiki/Bombyx_mori

· Silkworm Information – Insected Arizona, UA Center for Insect Science Education Outreach (n.d.) Insected Arizona, UA Center for Insect Science Education Outreach. Retrieved October 11, 2010, from http://insected.arizona.edu/silkinfo.htm

· Silkworm Cocoon – Articles on Cocoon (n.d.) Articles on Cocoon. Retrieved October 12, 2010 from http://www.cocoon.org/cocoon-articles/silkworm-cocoon.shtml

· Journal Article Review: General Information, Caring For and Breeding Silkworms (n.d.) The Silkworm Shop. Retrieved October 14, 2010 from http://www.silkwormshop.com/silkworm_info.html

· Pictures from: http://www.google.com/imgres?imgurl=http://www.webcastr.com/thumbnails/videos/indians-eye-silkworm-record-webcastr.jpg&imgrefurl=http://www.webcastr.com/videos/underground/chilli-record-attempt-in-india.html&usg=__Tdw-xXtLb6zb8X09YJ9_SCQnTCQ=&h=257&w=400&sz=40&hl=en&start=3&sig2=f-EdKGXk3GWrunHENFM0Pw&zoom=1&tbnid=9P2ubz3vaswMsM:&tbnh=80&tbnw=124&ei=xcm3TNXODYO88gbmrfCBCQ&prev=/images%3Fq%3Dsilkworm%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D1024%26bih%3D637%26tbs%3Disch:1&um=1&itbs=1

· http://www.google.com/imgres?imgurl=http://www.cirrusimage.com/Moths/caterpillar_anatomy.gif&imgrefurl=http://www.cirrusimage.com/Yellow_Bear_Caterpillar.htm&usg=__kGOE5b_DTR-HdefKEuNCQx3aIno=&h=280&w=508&sz=15&hl=en&start=0&sig2=WqqDSifsF4JqXGrzNCIevA&zoom=1&tbnid=gfQOEB3-ztBdyM:&tbnh=106&tbnw=192&ei=Dsq3TLutGsH48Aay-42FCQ&prev=/images%3Fq%3Dsilkworm%2Banatomy%26um%3D1%26hl%3Den%26biw%3D1024%26bih%3D637%26tbs%3Disch:1&um=1&itbs=

· 1&iact=rc&dur=291&oei=Dsq3TLutGsH48Aay-42FCQ&esq=1&page=1&ndsp=15&ved=1t:429,r:1,s:0&tx=55&ty=86

· http://entomology.unl.edu/images/silkworm/

· http://www1.ala.org.au/gallery2/main.php?g2_itemId=10549&g2_imageViewsIndex=1