Divide 12 cups of the sugar onto three half-sheet pans lined with parchment paper and add 4 tablespoons citric acid to each, if making sour worms. Spread into an even layer and set aside.
Whisk together the gelatin and 1/3 cup water in a 2-quart saucier. It will be clumpy. Set aside to bloom while you prepare the sugar syrup.
Combine the remaining 3/4 cup sugar, corn syrup, and remaining 1/4 cup water in a 2-quart saucepan over medium heat. Bring the sugar syrup to 160°F, about 3 minutes. Remove from the heat and pour over the gelatin. Return to low heat and whisk until the gelatin is completely dissolved, 2 to 3 minutes.
Remove from the heat and add the flavoring oil, food coloring and remaining 4 teaspoons citric acid, if using. Whisk to combine.
Pour the mixture into a squeeze bottle and cool to 100°F before squeezing shapes out onto prepared sugar pan. Work in batches, allowing the worms to set for at least 20 minutes before removing from the sugar. The gelatin can be reheated by dipping the squeeze bottle in a warm water bath and reheating to 100°F.
Alternately, drinking straws or candy molds can be filled. Allow the gelatin to set for at least 20 minutes before moving. For best results, leave the candy at room temperature overnight (8 to 12 hours) before storing in an airtight container or zip-top bag.