Sawtoothed & Merchant Grain Beetles

Oryzaephilus surinamensis oryzaephilus mercator

The Sawtooth & Merchant Grain Beetles appear brown to dark brown in color. The sawtoothed and merchant grain beetles are easily recognized by their flattened bodies and the six saw-toothed projections along each side of the prothorax. The sawtoothed grain beetle is distinguished from the merchant grain beetle by its smaller eyes. The area just behind the eyes of the sawtoothed grain beetle, however, is much larger than the same area on the merchant grain beetle.  These Beetles gorw to approximately 1/10 inch in size.

One female merchant or sawtoothed grain beetle may produce up to 285 eggs deposited singly or in small batches within the food. Larvae are active crawlers and move about through the food as they feed. They are scavengers and not capable of feeding on whole grains unless other insects have first attacked the kernels. After molting 2 to 4 times, the larva pupates and the adults emerge in about 7 days. The entire life cycle from egg to adult takes 27 to 50+ days, depending on the food quality and temperature. The female beetle lives from 6 to 10 months and several generations per year may occur.

Large populations of these beetles can develop in short periods, forcing adults to leave infested foods seeking new food sources. They have been known to invade every package or food stored near an infested food product. Infestations, therefore, are often widespread throughout a room or area. The merchant grain beetle can fly, but the sawtoothed grain beetle cannot.

These grain beetles are two of the more commonly encountered insects in processed grain, oats, pet foods and seeds. Merchant grain beetles are found more often in foods that are high in oils and fats, such as peanuts or birdseed.

Other foods attacked include rice, cereals, dried fruits, breakfast foods, grain meals, sugar, chocolate, drugs, pastas and tobacco. Its varied food preferences make it one of the most commonly encountered stored product beetles in retail food stores, warehouses and homes. In unheated grain facilities in northern states, breeding ceases at the onset of cold weather.