Make chocolate web and spider: On a sheet of parchment paper draw an 11-inch circle with a pen or pencil and draw a spider web on it, extending some of ends beyond circle. Tear off a large corner of the paper and on it draw a spider. Turn drawings over onto a large baking sheet.
In a metal bowl set over a saucepan of simmering water melt chocolate chips, stirring until smooth. Transfer chocolate to a pastry bag fitted with a #3 plain tip (slightly smaller than 1/8 inch). (Alternatively, form a makeshift pastry bag: Transfer chocolate to a small sealable plastic bag and seal bag, pressing out excess air. Squeeze chocolate to one corner of bag and snip off about 1/8 an inch from corner making a small hole.)
Pipe chocolate on web, beginning with spokes, and on spider. Freeze web and spider on baking sheet until very firm, at least 1