Mealworm Facts, Identification and Control
Scientific Order: Coleoptera
Common Family: Tenebrio molitor
Common Species in New York: The most common species is 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.
- Mealworms have evenly divided grooves resembling body segments running along the whole length of their abdomen.
- Newly hatched mealworms are a creamy white color; they turn their distinctive yellow-brown after a couple days.
- 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.
- Mealworms typically feed on anything they can find that is damp, decomposing, or generally moldy and old.
- Things like dead leaves and foliage, animal waist, or grain products that are past the end of their typical shelf life are their favorite things to eat.
- When it comes to your pantry, mealworms commonly foods like oatmeal, flour, cereal, oats, or similar dry goods.
- Mealworms feed continuously, stopping only to shed their skin, or molt.
- Mealworms are capable of using their hardened heads to burrow under food and moist dirt.
- When disturbed, adult beetles might release a foul-smelling chemical from a scent gland located in their abdomen.
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 three and twelve months.
Mealworms are born in late spring and early summer when the natural world provides lots of dark, damp shelter for females to settle down and lay eggs. A single female is capable of producing over three hundred of their small, white, bean-shaped eggs at a single time.
Larvae emerge from eggs after an incubation period of 18 days or less. Born a cloudy white color with segmented bodies, they turn yellowish-brown within days as they feed on the food around them. They’ll grow to about an inch long at this stage, shedding their skin multiple times in the process.
Mealworms stay in their larval state as temperatures drop, hibernating in this small, dark, C-shaped form and waiting until the next summer when they can emerge again.
After emerging from the pupa state, typically in early summer, adult mealworm beetles turn from whitish-orange to black (with occasional yellow markings) in a few days. Adult mealworm beetles grow wings, which they use to spread out, infest new areas, and seek mates. A single mealworm beetle can live between four months and an entire year.
Signs of Infestation
- The biggest sign of a mealworm infestation is seeing the mealworms themselves. They’re not particularly fast or sneaky, so if they’re in your home you'll probably see them.
- Mealworms may also leave bite marks or small holes in packaging for stored dry goods. When they eat cardboard or other packaging, they may produce a distinctive dry, paper-like waste.
Treatment and Prevention
- Your first step toward preventing mealworm infestations is removing potential shelters or food sources. Start outside your home by removing decaying material such as fallen leaves, compost, or old vegetation away from the perimeter of your home. Their ideal home is dark and damp, so keep that in mind when clearing out the outside of your home.
- Go through the dark corners of your home that can also provide food such as cabinets, closets, and storage areas. If you find any mealworms during this visual inspection, vacuum them up, then seal them inside of a plastic bag and dispose of it outside and away from your home.
- If you have found any mealworms during indoor inspections, it means that they had some sort of regular food source. While it may be unfortunate, we recommend removing any potentially infested food from your home, sealing it in plastic bags and disposing it away from your property to avoid reinfestation.
- Once you’ve removed them, don’t let your guard down right away. Check and recheck any damp, dark spaces (especially ones where you found previous signs of mealworms) for signs of their return periodically until you are sure that they are gone. After you've eliminated their food sources and most of the existing mealworms in your home, any remaining pests will likely search for food elsewhere.
- “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.