SEPARATE semi-sweet and orange morsels and place into separate uncovered, microwave-safe bowls.
LINE large baking sheet with wax paper.
MICROWAVE semi-sweet morsels and 1 teaspoon vegetable oil on HIGH (100%) power for 1 minute; STIR. The morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until melted. Pour melted chocolate onto prepared baking sheet. With small metal spatula or back of spoon spread chocolate into a roughly 12-inch circle. It does not need to be perfectly round.
MICROWAVE orange morsels and 1 teaspoon vegetable oil on MEDIUM-HIGH (70%) power for 1 minute; STIR. The morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until melted. Place open plastic bag into large glass or small bowl. Pour melted morsels into plastic bag; seal. Push mixture into corner of bag. Cut very small hole in corner of bag.
STARTING in center of the chocolate circle, squeeze melted orange morsels onto chocolate in circles, 1-inch apart until you reach the edge of the chocolate. Using a toothpick or wooden pick, starting in center, pull toothpick through chocolate and orange lines to edge. Then from edge, pull toothpick to center. Repeat until “web” is complete. Decorate edge of web with any remaining melted orange morsels.
REFRIGERATE for 20 minutes or until chocolate is firm and set. With edge of small metal spatula, lift web from wax paper and carefully transfer to serving platter. Place spiders on or around web. Make sure to remove them prior to breaking apart to eat.