Whisk together the instant pudding mix and milk in a large bowl until smooth. Let sit until slightly set, 5 minutes.

Whip the cream in another large bowl with an electric mixer on medium-high speed until soft peaks form, about 2 minutes. Add the cocoa powder and mix on high speed until stiff peaks form, about 1 minute. Transfer one-third of the whipped cream to the pudding and whisk until fully incorporated, then carefully fold in the remaining whipped cream with a rubber spatula.

Divide half of the pudding mixture among 6 clear cups or glasses (each 9 fluid ounces), filling them about halfway. Top each cup with 1 heaping tablespoon of the crushed cookies, then nestle 2 or 3 gummy worms and 3 or 4 candy eyeballs into the “dirt,” against the side of the cup so they are visible. Layer each cup with another heaping tablespoon of the crushed cookies and about 1/3 cup of the remaining pudding, then finish with 2 more heaping tablespoons of the crushed cookies. Refrigerate at least 1 hour.

Line a baking sheet with kitchen towels. To make the spiderwebs, fill a large bowl with crushed ice and a small amount of water. Press the ice down so the surface is as flat as possible. Transfer the melted wafers to a piping bag fitted with a medium round tip (or a resealable plastic bag with one corner snipped off). Pipe into the ice bath 4 intersecting lines to create a 3-inch asterisk, then pipe a circle just inside the asterisk and a smaller circle inside the first circle. Let the spiderweb set for 10 to 15 seconds then gently transfer to the prepared baking sheet. Repeat to make 8 spiderwebs; since they are fragile it is good to have a couple extra.

To make the spiders, arrange the gummy bears flat-side up. Use kitchen shears to snip 3 narrow triangles out of each short end, creating 4 legs on both sides of each spider.

Place a spiderweb on each dirt cup then top with a gummy spider. Serve cold.