Wash and dry the apples and remove the stems. Insert a wooden apple skewer or paper straw into each about halfway through (pierce first with a skewer if using straws). Line a baking sheet with parchment paper and spray it with nonstick cooking spray.
Microwave the marshmallows in a microwave-safe bowl for 30 seconds, then stir. Continue to microwave in 10-second increments, stirring after each, until fully melted. Let cool until just slightly warm to the touch, not hot.
Using both hands, grab the melted marshmallows with your fingertips and pull apart to create a "webbed" look. Wrap webs around each apple (see Cook's Note).
Place an edible chocolate spider on top of each apple to make this even more fun. Use melted chocolate to add 8 chocolate legs to a round chocolate candy, then use melted chocolate to "glue" candy eyeballs on top. Let set, then position on the web.