|MadSci Network: Zoology|
As you probably know, silkworms are the juveniles (larvae) of any of a number of species of moth, collectively called silk moths. The most common silk moth species, and the species used for nearly all commercial silk, is Bombyx mori. Like many insect larvae, the larvae of this species are highly "host specific", and will only eat Mulberry (Morus alba) leaves in nature. I have found some references to other plants being used as temporary food for silkworms in captivity, but this doesn't seem advisable, since the larvae would naturally only eat Mulberry, and may not be as successful on alternative diets. The other plants I have seen listed include lettuce, and two trees that grw wild in the US - Osage Orange ( Oclura pomifera) and Tree-of-Heaven (Ailanthus altissima). I've provided links to information about these species below.
It does seems advisable to feed your silkworms on Mulberry. You might be able to get a local nursery to donate a small mulberry plant, if you explain what you want to use it for. If not, they should be quite inexpensive to buy. Some companies also offer prepared silkworm food, made from mulberry leaves - this will obviously be more expensive than collecting your own leaves, though. Again, I've provided a link below. Many sites give detailed advice on how to raise silkworms, I've provided some links below, and some give hints about securing a supply of Mulberry leaves.
Other species of silk moth have silkworms that eat different plants, such as oaks, castor-oil plants and Polyanthus. Some silkworms are polyphagous, and will eat a variety of plants. These are extremely uncommon compared to Bombyx mori, and its highly unlikely that you'll come across these silkworms. The Indian silk industry, though, produces four types of silk, from different species of silk worm. Detail of these can be found at this page.
Good luck and enjoy your silkworms!!
Try the links in the MadSci Library for more information on Zoology.