Signs of Pests in Food

Stored Product Pests

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Merchant Grain Beetle


Color of Merchant Grain Beetle

Adults are typically a dark brown or dark reddish-brown. The larvae are a yellowish-white.


Adults are about 1/8" (3mm) long, with a flattened body. There are 6 saw-like teeth on each side of the prothorax, very similar to the saw-toothed grain beetle. They have well-developed wings, and are known to fly. Mature larvae are less than 1/8â?? (3mm).

Where Found

A truly multicultural bug, the merchant grain beetle can be found worldwide and easily tolerates cooler climates.


Adults can fly and are attracted to light. And with those saw-like teeth, they can chew into unopened paper or cardboard boxes, through cellophane, plastic, and foil wrapped packages.


Breathe easy. Your round kernels are safe! But watch the mac and cheese.

The merchant grain beetle cannot attack round kernels. Its flat body form lets it crawl through very small cracks and into imperfectly sealed packages. It is commonly found in oilseed products like nuts and cereal products, rolled oats, rice flour, cake mixes, macaroni, and cookies.


The female lays 22-190 white, shiny eggs either singly or in small clusters in crevices in food material over several months. The eggs hatch in a few days. The life cycle (egg to egg) typically requires 30-40 days, but may require over a year. Adults usually live several months.

Good Riddance

These insects contaminate more food than they consume, and usually are discovered leaving the infested food to crawl about. In any structure, good sanitation is the key, along with the immediate transfer and storage of products packaged in paper, cardboard, or plastic bags into tight sealing jars or Tupperware-type containers. Any infested product should be thrown away.