Mealworm Facts, Identification and Control
Scientific Order: Coleoptera
Common Species: Tenebrio molitor, or Yellow Mealworm, the larval form of the mealworm beetle, a species of darkling beetle.
- Size: The larval mealworms usually measure around ⅛ of an inch long. Adults can grow to around ½ an inch long.
- Color: Adults are dark with a hard shell and an average length of 1/2 an inch. The mealworms themselves (larval form of the beetle) are yellowish-brown with ringed, segmented bodies.
Signs of Infestation
Mealworms leave behind bite marks and small holes in packaging for stored dry goods. You may find small signs of damage or tampering on cardboard or other food packaging, particularly in dry storage.
When mealworms eat through packaging, they often produce a distinctive dry, paper-like waste. This waste looks somewhat dusty. You could find it both outside and inside of food containers.
Treatment and Prevention
Your first step toward preventing mealworm infestations is removing potential shelters or food sources. Remove decaying material such as fallen leaves, compost, or old vegetation away from the perimeter of your building. Next, go through each cabinet, closet, and storage area, especially where you keep food and other dry goods. The ideal mealworm infestation site is dark, humid, and warm, so look for the pest especially carefully in basements, warehouses, attics, and pantries.
Remove any mealworms you find using a vacuum, and throw out the food they infested immediately. If you find mealworms, check nearby food sources especially carefully as well. Recheck any damp, dark spaces for signs of mealworms periodically even after treating an infestation thoroughly.
Behavior and Diet
Mealworms typically feed on anything they can find that is damp, decomposing, or generally moldy and old. They're particularly fond of dead leaves, foliage, animal waste, and moldy or moist grain products. They'll frequently infest pantry items like oatmeal, flour, cereal, oats, and other dry goods.
Mealworms feed continuously, stopping only to shed their skin, or molt. As they feed, the larvae use their hardened heads to push and tunnel through food. Once inside the food, mealworms may be hard to spot at first. Fully-grown beetles lack the ability to burrow, but gain the ability to fly and release a foul-smelling chemical from a scent gland. They'll produce this foul scent whenever they're disturbed or threatened.
Reproduction and Life Cycle
Mealworm beetles go through four developmental stages: egg, larva, pupa, and adult. How long each developmental process takes is dependent on the temperature of the environment and how readily available food is. Their typical life cycle is between 3 and 12 months.
A single female mealworm is capable of producing over three hundred small, white, bean-shaped eggs at a single time. Larva hatch from eggs in 18 days or less and begin eating, moving, and infesting food products immediately. Mealworms may stay in their larval stage all winter if environmental temperatures are too low, but otherwise they'll eat and grow continuously, shedding their skin multiple times until they're fully grown. Adult beetles grow wings, which they use to seek out new mates.
- Mealworms have evenly divided grooves resembling body segments running along the whole length of their abdomen.
- Mealworms may look darker near the ends of their abdomen and head, and near each of their grooves or segments.
- Mealworm larva have hardened heads for burrowing underground.
- “UMaine Cooperative Extension: Insect Pests, Ticks and Plant Diseases.” UMaine Cooperative Extension Insect Pests Ticks and Plant Diseases, https://extension.umaine.edu/ipm/ipddl/publications/5044e/.
- “Mealworms.” Mealwormcareorg, http://mealwormcare.org/.
- “Mealworm.” Mealworm | Horticulture and Home Pest News, https://hortnews.extension.iastate.edu/mealworm.