Insect Pests of Home-Stored Foods Fact Sheet No. 5.501 Insect Series|Home and Garden by W.S. Cranshaw and F.B. Peairs* Several insects commonly infest home- Quick Facts stored foods in Colorado, such as grains, flour, nuts, spices, packaged herbs and • Indian meal moth, flour dried fruit. If infestations are prolonged, beetles, sawtoothed grain foods may be seriously damaged and may beetles and carpet beetles need to be discarded. Many people will (dermestids) are common discard food products that are even lightly pests of food items in infested by insects. These insects typically Colorado homes. pose little health hazard, although some species (notably carpet beetles) can produce • When insects that infest irritation or allergic reactions. food are first detected, try Indian meal moth, flour beetles and to identify all sources of Figure 1: Flour beetle. sawtoothed grain beetles are particularly infestation. common in Colorado homes and are found throughout most of the world. • To control infestations, Sometimes insects that infest food, such as use sanitary measures carpet beetles, enter homes through natural that remove food for the migrations. More often, insects enter homes developing insects. on food already infested during storage • Cold treatments can kill or transportation. insects in food items. Description • When using insecticides in and around food storage Flour Beetles areas, never allow chemicals Flour most commonly is infested by to directly contact the food. either of two closely related beetles: the Figure 2: Saw-toothed grain beetle. confused flour beetle and the red flour beetle (Tribolium, Figure 1). Small pieces of cracked grains also may be sources of flour Sawtoothed Grain Beetle beetle infestation. The adult flour beetles The sawtoothed grain beetle are reddish-brown and less than 1/8 inch (Oryzaephilus surinamensis) is the most long. They are sometimes called “bran bugs” common beetle found infesting household because they are so common in milling food in Colorado. It can develop in flour, operations. Both species of flour beetles have but most infestations occur in processed wings but rarely fly. grain products such as breakfast cereals, Immature stages are pale-colored and oatmeal, corn meal and pasta. Dried fruit and wormlike. On close inspection, a pair of chocolate also may be infested. pointed forks can be seen on the hind body The adult beetle (Figure 2) is about 1/10 segment. Development of the immature stage inch long, similar in size to the flour beetles. typically takes one to two months and adults It is elongate in body shape, flattened, and lay eggs over a period of five to eight months. distinctively marked with a series of saw-like Both adult and immature stages feed on flour. projections along the sides of the thorax. © Colorado State University However, because of its small size, some Extension. 3/96. Revised 12/08. magnification may be needed to detect these www.ext.colostate.edu characteristics. Sawtoothed grain beetles have *Colorado State University Extension entomologists wings, but have never been observed to fly. and professors, bioagricultural sciences and pest management. 12/2008 Spider Beetles When using Spider beetles (Ptinidae) (Figure 4) insecticides in the are a relatively rare pest of stored food home: in Colorado. They are larger than the other common stored-products beetles • Properly store insecticides within a and appear similar in shape to a spider. home. However, spider beetles have three pairs • Purchase only the amount of of legs, which distinguishes them from the insecticide you intend to use. eight-legged true spiders. Spider beetles can potentially infest Figure 3: Larder beetle. • Store insecticides and other a wide variety of animal or vegetable pesticides out of reach of children products. They are most commonly or pets. associated with grains, although they can eat feathers, wool, dried meat and other • Store pesticides away from heat or products. Infestations mostly occur when high moisture. these foods have been moistened and begun • Never store pesticides with food or to mold. food utensils. Eggs of the spider beetles are white and may be conspicuously laid about the food • Properly dispose of pesticides as products. The larvae are C-shaped and indicated on the label or according resemble small white grubs. Pupation of to local regulations on hazardous spider beetles often occurs in small cavities waste disposal. that they chew out of wood or other soft materials. Figure 4: Spider beetle. Eggs are laid in crevices in the food Indian Meal Moth supply. The larvae are yellowish-white with The Indian meal moth (Plodia a dark head and worm-like shape. Larvae interpunctella) is a common insect found feed on the same foods as adults. Under infesting food products in Colorado homes. optimal conditions, they can complete a Almost any coarse grains (oatmeal, grits, generation in less than two months. Adult etc.), nuts, seeds, dried pet foods, candy beetles may live for a year or more. bars, spices, cocoa, dried fruits or vegetables (e.g., chilis) are suitable materials for Indian Carpet Beetles meal moth development. However, flour is Several species of carpet beetles rarely infested. (Dermestidae) (Figure 3) occur indoors The adult stage of the Indian meal and outdoors in Colorado. They have moth (Figure 5) is about 1/2 inch long and extremely diverse feeding habits but prefer generally gray with bronze wing tips. The high-protein materials of animal origin, moth is the most common small moth such as wool and skins. Household lint, found flying in Colorado homes. Feeding dead insects or other debris are common damage is done by the larvae (“worms”), materials on which large numbers of carpet which are usually pale yellow to pink with beetles may breed. (See fact sheet 5.549, a dark head. When feeding, the larvae Figure 5: Indian meal moth adult. Carpet Beetles.) produce webbing that is mixed with food Infestations of carpet beetles in particles and droppings. Adult moths lay eggs near suitable pantries are less common than for flour or Indian meal moths occur throughout food, such as along cracks or folds of sawtoothed grain beetles. Carpet beetles the United States and most household packages. The newly hatched larvae are are relatively slow to develop. On cereal infestations originate from the inadvertent small and can penetrate loosely-closed products, they require about one year purchase of infested products. During packaging. When they reach a suitable for a generation. However, because the warm months, localized movements of the food, they begin to feed. Development can insects are highly mobile, infestations may moths also may occur outdoors, resulting be rapid under favorable conditions, and reoccur annually. in household infestations. Because of the the larvae ultimately grow to about 1/2 Carpet beetles are much more broad distribution of the insect, it is rarely inch long. Pupation occurs and the adult important as pests of woolens, furs and possible to definitely establish the original moths emerge. Adult female moths can other materials of animal origin. They are source of a meal moth infestation unless lay 200 to 400 eggs during their lifetime far more common and damaging to fabrics detected at purchase. of several weeks. Complete development than clothes moths in Colorado. of the Indian meal moth varies due to Control eggs, but have no residual effect unless When insects are first detected in spilled foods are completely eliminated. food products, try to identify all sources As a routine precaution, materials of infestation in the home. Check all suspected of having insects can be treated susceptible food items in cupboards. Pay by freezing after purchase. Purchase particular attention to items that have not smaller amounts of food and use food been used for a long time. Also check areas products directly after purchase to prevent of spilled foods. infestations from being established by If you know the identity of the insect, insects brought in on the food. it will help you focus your search. If flour Use of insecticides within the pantry beetles are present, look only through area is not generally recommended and finely-milled materials including crumbs normally will give little additional control and other spilled material. Sawtoothed in the absence of an aggressive sanitation grain beetles may infest a wider range of program. Some household formulations food, including oatmeal and coarsely milled of pyrethrins are labeled for use as crack food. Indian meal moths or cockroaches and crevice treatments near food storage infest pet food or bird seed and other areas. There are also some formulations ornamental items that involve the use of of pyrethroid insecticides (bifenthrin, grains or dried fruits and vegetables. Carpet permethrin, and tralomethrin) that allow general use in other areas of the home Figure 6: Indian meal moth. beetles most typically are established in woolens, furs, among dead insects and and may help manage insects that are household lint. widely dispersed. Never apply insecticides The physical presence of the insects in a manner that allows direct contact is the most obvious means of detecting with food or food utensils. Often it areas of infestation. Also look for old cast is best to remove all food and utensils skins left by flour and carpet beetles. The during insecticide treatment to avoid presence of webbing is an easy means to accidental contamination. detect items infested by Indian meal moth. Because of the diverse feeding habits Items infested by insects that live within and mobility of pests such as cockroaches the food (carpet beetles, flour beetles or and carpet beetles, controls must take place Indian meal moth) should immediately over a larger area of the home. be discarded or temperature treated to kill Always read and follow label directions Figure 7: Lesser grain borer. the insect.