Grain Beetle: All You Need to Know for Effective Pest Control

Grain beetles are a common pest found in stored grain products, often causing damage to food both at home and in storage facilities. One of the most widespread species is the saw-toothed grain beetle, known for its small, brown, and flattened body, measuring around 1/10 to 1/8 inch in length. These insects are not able to fly, and they are not attracted to light ^.

These beetles can infiltrate food products at various points in the supply chain, from manufacturing to retail ^. Typical items that may be infested include cereals, flours, pastas, dried fruits, dried meats, and candies. To prevent any damage, it’s essential to recognize the signs of infestation and take necessary precautions.

Identifying Grain Beetles

Sawtoothed Grain Beetle

The Sawtoothed Grain Beetle is a small insect with a flattened body measuring 1/10-1/8 inch long. They have six saw-like teeth on the first segment behind their head ¹. Common features include:

• Brown color
• Do not fly
• Not attracted to light

Larvae of these beetles are usually yellowish-white with a brown head and are less than 1/8 inch long when mature².

Merchant Grain Beetle

The Merchant Grain Beetle is similar to the Sawtoothed Grain Beetle but differs in the dimensions of the head capsule³. Key characteristics are:

• Brown color
• Prefers broken grain kernels
• Not suitable for egg-laying in intact kernels

Red Flour Beetle

The Red Flour Beetle is 1/8 inch long and has a brown to red appearance⁴. Specific features include:

• Clubbed antennae
• Eyes split above and below the head

Confused Flour Beetle

Confused Flour Beetles are similar to Red Flour Beetles, but with distinct differences in antennae and wing covers. Important features are:

• Reddish-brown color
• Slightly larger than the Red Flour Beetle
• Straight-sided antennae segments

Foreign Grain Beetle

Foreign Grain Beetles are small, reddish-brown insects with a preference for moldy grains. Key characteristics include:

• Wing covers with rows of fine hairs
• Thrive in high moisture environments
• Attracted to moldy food sources

Life Cycle and Habits

Eggs

• Saw-toothed grain beetles lay their eggs in grains and grain products.
• Hatching occurs within 7 to 10 days.

These beetles typically lay their eggs in food products like cereals, flour, pastas, or dried fruits, often found in pantries and warehouses ¹.

Larvae

• Larvae are yellowish-white with a brown head.
• Mature size is less than 1/8 inch long.

The larvae prefer feeding on broken grain kernels and “fines” ². Mills are often susceptible to infestations as they process grains, creating a suitable habitat with an abundance of food for larvae.

Adult Stages

• Adults are small and brown, measuring 1/10-1/8 inch long.
• Adults have six saw-like teeth on their first segment behind the head.

Adult grain beetles do not fly, thus they are not attracted to light ¹. In the adult stage, these beetles still infest pantries and warehouses, including both food products and other rooms adjacent to the pantries. Adult beetles can also be found feeding on a variety of vegetable products³.

Common Infested Items

Food Items

Grain beetles are known for infesting various food items, primarily those containing grain and cereals. Some examples include:

• Flour: Often used in baking, grain beetles can lay eggs and contaminate this common pantry item.

• Seeds: Wheat, barley, and oats are a few examples of seeds that may attract grain beetles.

• Pantry products: Items such as spices, pasta, and dry mixes can also be infested by these pests.

Pet Food and Animal Feed

Not just human food, grain beetles may also target animal nutrition options like:

• Pet food: Dry pet food, often containing various grains, can become a breeding ground for these beetles.

• Animal feed: Livestock feeds that contain grain components are also susceptible to infestation.

Non-Food Items

Oddly enough, grain beetles can also be found in some non-food items. A couple examples are:

• Cardboard: They may hide and reproduce in the crevices of cardboard boxes, especially if near food supplies.

• Cracks and crevices: Beetles may take shelter in small spaces within your home’s structure.

It’s important to take preventative measures to minimize the likelihood of these pests taking up residence in your home.

Prevention and Control

Sanitation

To prevent grain beetle infestations, cleanliness is essential. Regularly clean pantry shelves and other food storage areas to remove crumbs, spilled grains, or other debris. Vacuuming these spaces is also effective in removing potential food sources for beetles. Some examples of good sanitation practices are:

• Wipe down shelves with a damp cloth to remove food particles.
• Use a vacuum cleaner to suction away small debris.

Inspection

Inspect food packages for signs of beetle infestations before storing them in your pantry or food storage areas. Examine items such as cereals, flour, and pasta for signs of damage and discard any infested products.

Proper Food Storage

Ensure proper food storage to prevent beetle entry. Use airtight containers made of plastic, glass, or metal for storing food, as these materials help keep beetles out. Some examples of proper food storage are:

• Store grains in airtight plastic or glass containers.
• Use metal bins with lids to store larger quantities.

Temperature and Humidity Control

Controlling the temperature and humidity of food storage areas helps in discouraging beetle infestations. Grain beetles thrive in warm, humid environments; therefore, maintaining cool and dry conditions can help deter them from laying their eggs.

Pest Control Methods

Various pest control methods can be employed to deal with grain beetle infestations. Consider using non-chemical approaches such as traps or natural predators first, before resorting to chemical pesticides. Some pros and cons of different pest control methods are:

Professional Help and Resources

Hiring an Entomologist

An entomologist can help accurately identify and advise on control methods for stored product pests such as grain beetles. They have specialized knowledge and training in insect biology, which helps them devise tailored pest management plans. Some reasons to hire an entomologist include:

• Expert advice on pest identification and control methods
• Access to the latest research and industry advancements in pest management
• Ability to provide long-term pest prevention plans

For example, if you have a business in Texas and are struggling with grain beetle infestations impacting your profits, partnering with a local entomologist could be advantageous.

Home Pest Control Services

Home pest control services, like All-Safe Pest & Termite in Plano, Texas, offer professional assistance in dealing with various household pests, including destructive weevils and grain beetles. Here are some pros and cons of hiring a home pest control service:

Pros

• Convenient and hassle-free extermination of pests
• Regular treatment plans available for long-term protection
• Knowledgeable professionals who can identify and target specific pests

Cons

• Monthly or yearly service costs
• In some cases, chemical treatments may be used that could pose risks to humans and pets
• May require multiple visits for complete eradication

Special Cases

Foreign Grain Beetles and Mold

Foreign grain beetles are small, flattened insects, about 1/12 inch long and reddish-brown in color¹. They thrive in areas with high humidity, typically near mold growth.

• Often found near mold or damp environments
• Can be a sign of moisture problems in a building

For example, if you find foreign grain beetles in your pantry, it could indicate moisture or mold issues.

Beetles in Sheetrock

In some cases, foreign grain beetles can infest sheetrock, due to its porous nature, which can retain moisture and promote mold growth. This can be both a nuisance and a sign of structural damage.

• Infestation can lead to property damage
• May indicate hidden mold issues

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Grain Beetles

Subject: Tenacious ”grain” beetle
Location: Columbus ohio
September 21, 2013 5:10 pm
We cannot make these go away! We clean and toss everything and they come back to our kitchen pantry. As it happens we are getting new cabinets and do not want to see them on our new shelves!!! Help
Signature: Beetle mania

Dear Beetle mania,
We believe this is most likely a Merchant Grain Beetle, Oryzaephilus mercator, but we would not discount that it is the closely related Sawtooth Grain Beetle, Oryzaephilus surinamensis.  Both species of Grain Beetles have similar habits, and according to BugGuide, they feed upon:  “larvae and adults feed on damaged kernels of stored grains: barley, oats, rice, sunflower seeds, and wheat, plus flour, pasta, breakfast cereals, cake mixes, and various other processed foods.”  If you cabinets are very old, it is possible that over the years, flour and other pantry items have spilled into cracks and has filled nooks and crannies in the cabinetry that is sustaining a population of Grain Beetles even if you have discarded all items that might be feeding them.  Hopefully replacing the cabinets will solve your problem.

We certainly hope so, thank you so much!
Misha Z.

Letter 2 – Grain Beetles

What is this and how do I get rid of it?
January 12, 2010
Hello!
For the past two months we have had these small bugs infesting our kitchen. We thought maybe they were just coming in from the cold, but now we cannot get rid of them.
They are small (less than 5mm), blackish-brown, I think they have 6 legs and 2 antena but it’s hard to tell. They are only on our countertops and occassionally we find them on the floor in our kitchen. They do not get into our cupboards. They do not jump, just crawl.
We have tried several sprays for ants, roaches, sowbugs, beatles, gnats, spiders, flies…pretty much everything that we could think of. Obviously we’re not getting the right kind of stuff.
Any help you can give in determining what kind of bug this is and how we can get rid of it would be great. Sorry the picture is not very helpful. I can’t get a closer shot that’s clear.
Let me know if you need any more information.
Thank you!
Holly Grant
Tonawanda, NY (north Buffalo near Lake Erie)

Hi Holly,
Earlier this morning, we posted another image of a tiny beetle that is infesting a home, but in that case, we are uncertain of the species.  Your beetles are either Merchant Grain Beetles, Oryzaephilus mercator, or Sawtooth Grain Beetles, Oryzaephilus surinamensis,two species in the genus Oryzaephilus.  These beetles will infest grains and according to BugGuide:  “larvae and adults feed on damaged kernels of stored grains: barley, oats, rice, sunflower seeds, and wheat, plus flour, pasta, breakfast cereals, cake mixes, and various other processed foods used for human consumption
Life Cycle  female O. surinamensis lays 45-285 white, shiny eggs singly or in small clusters in crevices in the food material during a 2-5 month period; eggs hatch in 3-17 days depending on temperature; larva passes through 3-5 instars and usually constructs a pupal cell or cocoon from food particles held together with sticky oral secretions; larva attaches anal end to some solid object to pupate; life cycle typically 30-50 days (range 27-375); optimal developmental conditions 30-35 degrees Celsius and 70 percent humidity; as many as 6-7 generations per year, depending on temperature and food supply; adults typically live 6-10 months but may live longer than 3 years.”  BugGuide also indicates that they can be found:  “in containers or buildings where grain is stored; adult O. surinamensis cannot fly; adults of O. mercator are strong fliers but are not attracted to light.”  We would suggest that you inspect the pantry closely to identify the source of the infestation.  Extermination will not help unless all of your food is sprayed with pesticide, which is not a healthy option.

Letter 3 – Grain Beetles

Bugs finding their way inside my dry foods
September 4, 2009
Dear Bugman,
These are little (1 to 1.5 mm in length) black bugs that are beginning to appear everywhere in my apartment. Inside a box of oatmeal there were hundreds. Inside bags of rice, flour and sliced almonds, again, they appear. I’ve had to waste a lot of food recently because they keep finding their way overall.
In of the pictures attached, you see one that crawled inside a photo frame and died because he was trapped between the glass and the picture. Crazy.
I live in Dubai, UAE, and I suspect these are some sort of desert bug. Also, there is high humidity here, as we live in front of the sea.
Please advice: are these disease-carrying critters? How do I get rid of them?
You can see their size relative to the grains of rice on the pic attached.
Thank you!
Fran
Dubai, United Arab Emirates

Dear Fran,
You have Grain Beetles in the genus Oryzaephilus, either the Saw-Toothed Grain Beetle or the Merchant Grain Beetle.  In your case, we don’t believe exact species identification is an issue since both species have similar habits.  The Grain Beetles are lumped together with other stored food pests and are collectively called Pantry Beetles.  According to Charles Hogue in his book Insects of the Los Angeles Basin:  “Several species of small beetles are counterparts to the pantry moths in that they infest dried food products.  Though the larvae rarely consume an appreciable quantity of the food, their presence alone is sufficient to render it unpalatable.  Pantry beetles are likely to be found in all kinds of dry organic material used by people as food.  They may infest such common foods as dry breakfast cereal, rice, oats, wheat, peas, candy, spices, dried fruit, noodles, and spaghetti, nuts, pet food, and beans as well as materials not usually thought of as food, including tobacco, red pepper, drugs, herbs, and even certain types of upholstery stuffing.”  We would add dried mushrooms to Hogue’s relatively comprehensive list of foods.  Later Hogue writes:  “The appearance of these pests in a tightly sealed package of dried food is a source of wonder to housekeepers.  Entry is commonly by way of minute imperfections in the seal, but some species may bore through paper and cardboard containers to get at the contents.  In other cases, infestations occur when the foods are stored in bulk in railroad cars, warehouses, and at other stops along the processing line.”  This means you may have introduced your current infestation by purchasing food that was already infested.  Our best advice is to clear out your pantry in its entirety and begin anew.  Do not store dried foods for lengthy periods of time and use containers with tight seals.  Some species of Pantry Beetles, according to Hogue:  “act as intermediate hosts and vectors of the human tapeworms Hymenolepis nana and H. diminuta.  People acquire infections by ingesting beetles containing the larval (or cysticercoid) stages of the tapeworm, which will often remain viable in infested corn meal and wheat flour that is undercooked.”

Letter 4 – Grain Beetle

Subject: Bug found in kitchen
Location: Austin, TX
February 5, 2015 7:01 am
I’ve been getting some kind of bites so I’m trying to find the culprit. Doing all the normal bed bug searching but hopefully another critter is responsible. I found this guy on the kitchen counter.
Signature: Austin guy

Dear Austin guy,
This looks to us like one of the Grain Beetles in the genus Oryzaephilus, which includes two species that infest stored foods and have cosmopolitan distributions.  According to BugGuide:  “larvae and adults feed on damaged kernels of stored grains: barley, oats, rice, sunflower seeds, and wheat, plus flour, pasta, breakfast cereals, cake mixes, and various other processed foods” so you may want to check the items in the pantry to locate the source of your infestation.  In our opinion, they have no connection to the bites you are getting.

Will do. Thanks so much for the quick reply. I really appreciate it.