Pour the lime gelatin into a mixing bowl and add the boiling water. Stir until the gelatin fully dissolves.
Add the cold water, tequila, fresh lime juice, and orange liqueur to the bowl. Stir until the mixture is smooth and combined.
Divide a small portion of the mixture into a separate small bowl and stir in the black food coloring until the color is even.
Fill each plastic shot cup about three-quarters full with the green mixture. Let the cups sit for 10 minutes so the surface firms slightly.
Dip a toothpick into the black mixture and draw thin lines across the surface of each shot to form a spiderweb pattern. Repeat for all cups.
Place the cups in the refrigerator for at least 4 hours until fully set.