Pantry Pests

Pantry Pests

Flour Beetles Description & Biology Common flour beetles include the confused flour beetle and the red flour beetle. They are similar in habits and appearance. Both beetles primarily infest flour and, to a small extent, foods made of processed grains. Confused flour beetles and red flour beetles are often found together. Even though they cannot attack whole grains, there are usually enough broken kernels and grain dust, caused by the rubbing of grain during handling, for these beetles to survive. Any home can be invaded by these beetles through the transportation and storage of grains or grain products such as cereals, macaroni, flour, etc.

Flour beetles are not known to carry or spread any diseases that affect humans. Nor do they attack anything other than grain or starch foods (at least not for long). However, in search of their favorite foods, they may become an annoyance, invading all areas of a home.

The beetles (adults) are shiny, flattened, reddish brown insects about 1/7" long, and very active. The larvae are brownish to yellowish white, worm-like insects with three pairs of legs. They are about 1/16" when fully grown.

Both beetles can live up to three years. Unlikely to survive winter temperatures, they seek protection in heated areas or areas where high moisture grain is heating. Generally, these insects are considered weak fliers, but warm temperatures make them more active and, with the help of a wind, they can apparently move long distances.

Larder Beetles Description & Biology

Larder beetles, as their name implies, prefer meat or meat by-products. This could be decomposing animal, poultry, insect or other non-plant materials. Mounted animals may also become infested. However, larder beetles can survive on other organic materials too. Infestations in homes most likely come from infested dry dog and cat food or bird feed. It is not unusual to find new infestations where rat or mouse baits have been used. The beetles can infest the baits and also the vermin carcasses.

Grease from food preparation and cooking also attracts larder beetles. Any food that is not in a tight container, and has not been used for a month or more, should be checked for infestation whenever beetles or larvae are found.

The adult larder beetle is about 3/8 inch long, black with a lighter stripe across the middle on which there are six small black spots. A full grown larva is about 5/8 inch long, somewhat fuzzy, with two distinct spines on top of the back end that curve backward. When mature, the larvae can become even more destructive by chewing holes into wood, in which they pupate.


To lessen the chances of larder beetle infestations, store food in glass, plastic or metal containers with tight fitting lids.The first step in controlling larder beetles is looking for the source of infestation. If you find an infested product or item, do not throw it away before destroying the infestation. To kill insects in a package that you intend to throw out, place the package in an oven at 125 to 140F and heat for 30 minutes to fully penetrate the package. Other means of destroying the pests is to place the package in a freezer at -20F for a week, or spray with an insecticide. Only then should you discard the infested package. This will keep the pest from spreading.

Mealworms Description and Biology

The mealworm larva is yellowish to brown with a smooth, shiny, wormlike body. It is about 1/8" thick and is usually 1 to 1/4" long when mature and ready to pupate. The emerging adult (beetle) is black and about 3/4" long. After mating, the female can lay up to 1,000 eggs which hatch in less than 18 days. The newly hatched larva takes six to nine months to mature. The life cycle (egg to egg) usually spans somewhat more than a year; however, under ideal conditions it can be completed in as little as four months. Mealworms can be found in moist grain in dark and undisturbed areas. The normal operations of feed grain systems would not suit them, but waste, dusty, or damp areas create a favorable haven. Although they feed on cereal products used in homes, such an environment ordinarily would not meet the insects needs.

Mealworm outbreaks usually occur where grains are processed and stored. Litter remaining in old or abandoned poultry houses appeals to these insects, and explosive populations have created severe problems for residents within 1/2 mile of the source of an infestation.


Early detection through good management is important. Keep the food in a tightly covered container and clean containers frequently. Do not overlook dry dog or cat foods.

Infested grain must be removed from storage and disposed of or used. Before it can be used, the grain must be treated with insecticide. Waste products must also be treated unless they are buried in a sanitary landfill. Infested poultry litter must be handled the same way unless it is spread over the ground and plowed under. Poultry litter simply dumped outside on the ground can become infested by beetles scattered in the area. Call the Pest Management Office for recommendations on treating large quantities.

Those bothered by mealworms should remember never to discard infested food without first killing the insects. This is best done by placing the infested food in a container and heating it in an oven at 130 F to 150 F for 30 minutes long enough to reach this temperature. Then discard the food. Placing infested food in a freezer for five days or so should also kill the insect in all stages of development. A vacuum cleaner can be an effective tool. Discard bags sealed in another plastic bag to help prevent spread of infestation. A household aerosol insecticide can be used inside the home, but the results may be disappointing because other mealworm beetles may come in from outside.

Lesser Mealworms Description and Biology

The lesser mealworm may be found in any area where there is damp or moldy manure, litter, grain, milled products, or spoiling food. These conditions are usually found wherever there is livestock or poultry. High populations of the beetles may become a nuisance to farms and surrounding communities.

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 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.

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.


When areas around homes are infested with lesser mealworms, reduce the light visible from the house and put on a light elsewhere to attract the mealworms. Sevin, diazinon, or malathion may be used to treat a 5-to-10 foot perimeter around the house to kill beetles hiding in grass, under shrubbery, siding, porches, etc., during the day. A blacklight electrocuting unit placed in an area away from the house may also help.

Strawberry Root Weevil Description and Biology

There are more than 20 species of root weevils that attack strawberry in the United States. In the Northeast, the three major species are the black vine weevil, Otiorhynchus sulcatus (Fabricius), the strawberry root weevil, O. ovatus L., and the rough strawberry weevil, O. rugostriatus Goeze. Root weevils are also pests of raspberries and rhododendrons.

The root weevil adult is a brown to black beetle, with rows of pits or punctures along its back. Like other weevils, its mouthparts are extended into a snout. The three species discussed here look similar but differ in size. The strawberry root weevil is the smallest in size, about 5 mm (0.2") and black to light brown; the rough strawberry weevil is generally an even chocolate brown and 6.4 mm (0.25") long; and the black vine weevil sometimes has small flecks of yellow on its black body and can reach 1 cm (0.4") in length.

Adults of Otiorhynchus generally emerge in late May through June from puparia in the soil. They feed at night on foliage and hide during the day. After a period of approximately 30 to 60 days (for the black vine weevil) or 10 to 14 days, they begin to lay eggs. Some larvae of these species do not pupate in the spring and will remain in the soil throughout the summer. They then pupate in the fall and overwinter as adults, to emerge the following spring.

Depending on the species, peak egg laying occurs from late July through August. Eggs are laid in the soil around the plants; they are pearly white when laid, but soon change to an amber color. Eggs of the strawberry root weevil are 0.4 mm by 0.5 mm (0.02" long); those of the black vine weevil are 0.6 mm (0.03") spheres.

Larvae, or "grubs," are creamy-white or dirty-white to brown, have no legs, and lie in a characteristic "C" position in the soil. Grubs of the strawberry root weevil are about 6 mm (0.25") long when fully grown; those of the black vine weevil are 12 mm (0.5") long. By October, most of the eggs have hatched into larvae; hatching occurs about ten days after the eggs are laid. Young larvae feed on fine roots and crowns in mid-summer, overwinter in the soil, and cause their heaviest damage in the spring. Black vine weevil pupae are soft and white. Adults emerge after a short pupation period in April and May. There is only one generation per year.


Adult root weevils eat notches in the leaves, but this damage is seldom important. The larvae, however, cause serious damage by tunneling in the roots and crowns as they feed on strawberry plants. Most damage to the roots is caused by the later instars of larvae in March and April. Plants become stunted and darkened, and this damage can weaken or kill the plant. Injured plants have a stunted appearance; the leaves are closely bunched and are dark and blue-green. The fine roots have been destroyed, and sometimes even the hard fibrous roots have been eaten.

Heavily damaged areas in the field can be large--sometimes up to 0.2 ha (.5 acre)-- and circular, because of the beetles' behavior of gathering in groups. Without control, damage can be so severe by the second fruiting year that early termination of the planting is necessary. Newly transplanted strawberry plants can be particularly susceptible to black vine weevils.


Because there are three or more species of root weevils in the Northeast, precise identification is essential for adequate control. Adults should be collected for proper identification.

To prevent the spread of insects to other beds, plow under old beds as soon as possible. Rotate fields to an unsuitable host (e.g. corn, pumpkins) for at least two years. Fall plow infested beds. These pests do not fly. Keep new beds far from infested sites and clean farm equipment before moving from infested fields to new fields to prevent them from spreading.

Strawberry Rootworm Description and Biology

The adult form of this insect are beetles that are small (1/8") round, and copper-colored with dark markings on their backs. The immature root-feeding grubs are also small (1/8"), creamy white in color with 3 pairs of legs, and are actively feeding on roots in the late spring to early summer. The new generation of adults appears after renovation (late July or early August).


This insect can be most easily observed in the field as adult beetles feeding on leaves. Feeding occurs at two times in the growing season in Massachusetts (May and July-August), and results in shot-holes in the leaves. In Maine, the second feeding period may extend into October. The second feeding period usually is more evident because a greater number of beetles are feeding then. The earlier feeding is done by the overwintering population.


As with all root-feeding insects, control of the root-feeding stage is very difficult. Therefore, control measures for strawberry rootworm should be directed toward the adult stage of the insects. Presence of adults can be detected by the feeding injury or direct sightings of the adult beetles in the field. Sticky traps used for monitoring tarnished plant bug may aid in sighting strawberry rootworm adults since they feed primarily at night. Some of these beetles find their way onto the traps.

If feeding injury is observed in May or June, an insecticide spray at this time will reduce the number of egg laying females and therefore, the number of grubs feeding during the summer. When the next generation of adults emerges in July or August, control measures may be needed again.

Striped Cucumber Beetles Description and Biology

The striped cucumber beetle is one of the most damaging pests on cucurbits, such as squash, cucumber, melon and pumpkin. The larvae can cause severe damage to roots. A single beetle can cause severe damage to an emerging plant by feeding on the lower surface of leaves. Next generation adults (overwintering) are known to feed inside flowers, preventing pollination and fruit set. These beetles also spread bacterial wilt, cucumber mosaic, and squash mosaic virus.

The striped cucumber beetle is about 1/5 inch long, and has a black head and yellow-green wing covers with three black stripes. The orange-yellow eggs are laid near the base of host plants. The slender white larva grows to about 1/3 inch long and is dark on each end. There is one generation per year.

Only unmated adults overwinter. They overwinter under leaves, rotten logs or almost any other debris on the ground. They emerge in the spring when soil temperature reaches 55F. Then the beetles feed on pollen, petals and leaves of willow, apple, hawthorn and more specifically, on their alternate hosts of goldenrod, aster, etc. As soon as cucurbits, the preferred hosts, come up or are transplanted, the beetles fly to these plants to start feeding and mating.

In a few days, the female lays eggs in the soil. The eggs hatch in about 10 days. The larvae work their way to the plant roots where they feed for the next 2 to 6 weeks, sometimes causing severe damage. The mature larvae pupate in the soil. The adults emerge in 7 to 10 days. These beetles are not usually seen the rest of the summer except when feeding in cucurbit flowers.


Because overwintering cucumber beetles are around by the time cucurbits are up or transplanted, it is important to check at least daily to control the pest. Handpicking is most effective if done early in the morning when most feeding occurs. These beetles are easy to kill, but because more keep arriving on the plants, it sometimes seems as though controls are not effective. Barriers of row covers, cheesecloth, etc., can protect your plants; remove by midsummer to permit pollination.

Removal of goldenrod, aster, etc., from the vicinity of cucurbits helps reduce the number of beetles. Removing plant debris or keeping it to a minimum is also advisable.

Cigarette Beetle Description and Biology

The cigarette beetle is one of the most common household insect pests along the Atlantic Coast and Gulf Coast States. It can be found throughout the year, but seems to be more common in the fall and winter months. The cigarette beetle is native to Egypt. In fact, a beetle was found in King Tutankhamen's tomb! In the 3,500 years since, it has hardly changed.

The adult beetles are small, squat and oval, about 1/10 inch long, and are covered with small hairs which give them a silky, yellowish-brown color. The antennae are saw-like and the head is retracted. Many times it is mistaken for the Drugstore Beetle, when identified with the naked eye. Adults are strong fliers and prefer subdued light and temperatures over 65 degrees Fahrenheit. The adults tend to fly in late afternoons and on cloudy, overcast days.

As its name implies, the cigarette beetle is a pest of dried tobacco either in the stored, bundled form or in cigars, cigarettes, and chewing tobacco. This particular species infests tobacco wherever it is stored but is also found infesting many homes. It also feeds on the bindings and leaves of books. The larval stages of the cigarette beetle can feed on a variety of stored products including grain, cereal products, pet foods, rat and mouse baits, pasta, ginger, raisins, rice, dates, pepper, dried fish, drugs, belladonna, dried flower arrangements and seeds. The larvae have been known to feed on upholstered furniture, particularly stuffing. The adult Cigarette Beetle can also feed on pyrethrum powder that is strong enough to kill cockroaches! A serious pantry pest, their range of food makes them difficult to control. There have been larval infestations in dried flower arrangements, causing the flowers to drop or all the petals to fall.

The female produces about 100 eggs, which are deposited on or near the available food supply. These eggs then hatch within 6-10 days. The wormlike larvae are slightly smaller than the adult beetles. Larvae are creamy white except for the yellow head and brown mouth parts. Larvae become full grown in about 40 days. The entire life cycle can be completed in 45-50 days, and there may be 3-6 overlapping generations per year in warmer climates, while one generation per year might be seen in more temperate locations.


The first step in control of the cigarette beetle is to find the source of the infestation. This means inspecting all of the dried foods in the infested cabinets or drawers. Once the infested material is found, it should be destroyed or frozen for 5-10 days. Clean all the cabinets and drawers with a vacuum cleaner (then throw the cleaner bag away!).