Mealworms must molt in order to grow. The skin of the mealworm splits down the back and the mealworm slides out. When this happens, the mealworm is white. This is a sure sign that the mealworm has molted recently.

What color should mealworms be?

The mealworms are common, widespread insects that occasionally infest stored products. The larvae are elongate and cylindrical ("worm-like"), hard-bodied and yellow to golden brown in color. The mealworm adults are nocturnal, black, hardshelled beetles about one inch long.

How long does it take for mealworms to turn into beetles?

The fully grown larvae (mealworms) are golden brown and a little over one inch long. The larvae come to the surface of the substrate, turn soft and plump, and then transform into naked white pupae that turns yellowish brown. The pupae don't eat or move much. After about 1-3 weeks the pupae metamorphose into beetles.