Description & Biology

Adult lesser mealworms are black or dark reddish brown and are about 1/4" long. They can move quite rapidly. The yellowish brown larvae, look wormlike and are about 3/8" long. The 200 to 400 eggs laid by each female are usually found in crevices of grain.

While feeding and growing, the larva will molt 7 to 11 times in the 48 days it takes to become a pupa. The pupal stage will last an average of 7 days, adding up to a total of 60 days from egg to adult. The newly emerged female will start egg laying in about 11 days. The lesser mealworm will complete one cycle, egg to egg, given generally favorable temperatures and diets, in approximately 71 days. The larvae and pupae are rarely seen because they hide under boards, in litter, etc. The adults are nocturnal. Few commercial poultry operations in Maine are free of these beetles. Because the creatures live in litter, it is generally believed that they cause no damage or problems. However, lesser mealworms are known to attack the digestive tracts of sickly birds. Also, mealworms are aggressive, destroying the eggs and larvae of beneficial insects such as predaceous mites and pseudoscorpions that may also be attracted by the litter. Mealworms are also credited with destroying the eggs and larvae of nuisance insects such as fly eggs and maggots. In some states, the insect is introduced into new chicken houses or freshly cleaned houses to aid in fly control. But in many cases, high populations of beetles have failed to reduce or control fly populations in Maine.

One concern regarding the use of mealworms to control indoor flies is that some larvae will migrate to walls, where they may chew holes in foam and fiberglass insulation and wood to create spaces for pupation. However, most of the pupae are found in manure. Of greater concern is the dispersal of beetles when litter is piled or spread in fields. Some areas have had severe problems as a result, with hundreds of these beetles invading nearby homes.

Because lesser mealworms are widely distributed and their food and habitats are found in many rural areas, it seems unlikely that a farm could ever be kept entirely free of the insects. Populations must be kept as low as possible because lesser mealworms can spread certain poultry diseases and damage insulation.

Management