Adult Mealworms are about 1/2 inch long. The Yellow Mealworm is a polished, shiny black or brown, whereas the Dark Mealworm is a dull black. Both species have well-developed wings and are readily attracted to lights. The larvae are 1-1/4 inches long when fully developed. They are cylindrical, hard-bodied insects very similar to wireworms. The Yellow Mealworm larva is bright yellow, while the Dark Mealworm larva is dark brown.
The larvae are found in dark, damp undisturbed locations feeding on collections of grain, grain dust, or cereal products. Mealworms overwinter as larvae, emerging in the spring as adults that soon begin egg laying. Although the adults only live for two to three months, the insects may remain in the larval stage for as long as 600 days.
The first step in controlling a mealworm infestation is finding and eliminating the source of the infestation. Areas to search and clean include beneath cabinets, beneath baseboard areas, grain storage areas, or any other location which may hold moisture and food for the developing larvae.