By: W. WAYT GIBBS

When I was 10 years old, I took a bet from a fellow sixth grader and, in front of the whole class, choked down a panfried earthworm. Of all the weird foods I’ve eaten—and there have been quite a few—that was by far the creepiest.

With a little advance planning, you can make a treat for this Halloween that gives your guests the willies but actually tastes great. Imagine their reaction when you uncover a serving tray piled high with cookie-crumb “dirt” filled with wiggling gummy night crawlers. Then turn out the light, switch on a black light, and enjoy the gasps as the edible worms emit an eerie blue glow, thanks to a tasty fluorescent liquid that you might already have in your pantry.

These treats are fairly easy to make once you have all the needed supplies. And kids will enjoy helping with the preparation, if you don’t mind spoiling the surprise. To make worm-shaped gummy candies, our research chefs use night crawler fishing-lure molds purchased from a sporting goods store. But other mold shapes will work as well; this time of year, it’s easy to find candy molds for skulls, spiders, rats, eyeballs—whatever sends a shiver down your spine. Shallow molds work best.

Two special ingredients combine to yield that smooth, stretchy, yet tender texture you want in a gummy candy. The first is gelatin, which comes in various strengths measured by a unit called Bloom (after Oscar Bloom, who invented the gelometer, a device that measures jelly strength). The recipe works best with 200 Bloom gelatin, sometimes called gold gelatin. If you can’t find it, you can substitute Knox-brand powdered gelatin, which has a Bloom strength of 225. Just reduce the amount used from 20 grams to 18 grams.

The second unusual ingredient is gum arabic, which is made from the hardened sap of acacia trees. The gum gives the candies a smooth, shiny surface while remaining pliable. It’s fairly pricey stuff, but you only need a little bit. Look for it online in powdered form.

And that secret ingredient that glows under black light? Quinine, which is used to flavor tonic water. This medicinal chemical, originally isolated from the bark of a South American tree, is so highly fluorescent that it sends out about 55 photons of visible blue light for every 100 photons of ultraviolet light (also known as black light) that it absorbs. If you don’t already have a black light, get the kind that uses fluorescent tubes: they emit a wider range of wavelengths than LED lights do and will make the quinine in the candies glow more vibrantly.

To obtain the right texture for these candies, it is crucial to use the correct proportions of ingredients.