Go to the hardware store and buy a can of Durhams Rock Hard Water Putty. Find a small container that is 1/2" to an 1" deep that is wide enough to put for to 6 worms across. I have used various things like the top to a kids shoe box. Take your worms and glue them to the bottom of the box so they will remain stationary. Follow the instructions on the can and mix up enough putty to fill the box. Once it is mixed slowly pore the putty over your worms and fill the container. Let this stand untill hard. Turn the contanor over and gently work the block of hard putty out of it. The worms will stay on the container and they will leave a nice cavity of themselves in the putty, you may need to trim the edges some. I then coat the block with shelack. After this dries you will have a mold that you can poor hot plastic into. This is very economical. They are fragil. If you drop one it will shatter like glass. You can also buy molds and mold making material at www.lurecraft.com. I have some of their molds and they are good and will last longer than the putty but will be more expensive. They also sell plastic,sents and coloring. Hope this helps.
Dave