Foreign Grain Beetle: All You Need to Know in a Nutshell

The foreign grain beetle is a common household pest that can be found in a variety of settings, particularly where damp, moldy grain and other materials are present. Being a small and flattened insect, it has a reddish-brown color and measures about 1/12 inch long. Under magnification, you will notice two peg-like projections behind its head which help differentiate these beetles from similar insects like fruit flies or gnats UMN Extension.

These beetles are known to be strong fliers, typically becoming more abundant during late summer and fall. Their diet mainly consists of molds and fungi that grow on damp grain and grain products Plant & Pest Diagnostics. In addition, they are often found in close proximity to grain processing facilities where damp, moldy grain tends to accumulate.

Foreign Grain Beetle: An Overview

Identification and Characteristics

The foreign grain beetle (Ahasverus advena) is a small, flattened insect. Its key features include:

• Color: Reddish-brown
• Size: About 1/12 inch long
• Two peg-like projections on the thorax

These beetles can be confused with fruit flies or gnats due to their size and strong flying abilities. However, their hard shell sets them apart from flies.

Biology and Life Cycle

The life cycle of foreign grain beetles consists of four stages: egg, larva, pupa, and adult. They primarily feed on molds and fungi, particularly on damp grain, grain products, and other materials.

Habitat and Distribution

Foreign grain beetles have a global distribution. They are commonly found around grain processing facilities where damp, moldy grain accumulates. Their habitat preferences include:

• High humidity environments
• Locations with damp, moldy grain

By understanding their identification, biology, and habitat, we can better manage and prevent foreign grain beetle infestations.

Infestations and Impact

Foreign Grain Beetles in Homes

Foreign grain beetles (Ahasverus advena) are small, reddish-brown insects, which can infest homes, typically in areas with high humidity and moisture like basements and kitchens. These pests can enter through:

• Cracks and crevices in walls
• Open windows and doors

In new homes, they are attracted to moisture in wood and wet building materials. However, their presence is harmless to humans and pets.

Characteristics of foreign grain beetles:

• About 1/12 inch long
• Reddish-brown color
• Hard shell
• Two peg-like projections behind the head
• Strong fliers

Damage Caused in Grain Storage Facilities

Foreign grain beetles are known for infesting grain storage facilities. They cause damage by feeding on molds and fungi growing on damp grain and grain products. The infestation can lead to spoiled grain, resulting in financial losses for facility owners.

Examples of damage:

• Reduced grain quality
• Grain contamination
• Spoilage

Nuisance and Harmlessness

Though foreign grain beetles are pests, they are harmless to humans and pets. They do not bite, sting, or transmit diseases, but their presence can cause discomfort and annoyance by flying around living spaces.

Nuisance factors:

• Can be confused with fruit flies or gnats
• Presence in rooms and living areas
• Annoying flying behavior

Harmless factors:

• Do not bite or sting
• Do not transmit diseases

In conclusion, it is essential to be aware of the infestations and impacts of foreign grain beetles to take preventive measures and maintain a hygienic living environment.

Signs of Foreign Grain Beetle Presence

Moldy Conditions

Foreign grain beetles thrive in moldy and damp conditions. They primarily feed on molds and fungi growing on damp grain, grain products, and other materials¹. Watch out for:

• Dampness in storage areas
• Signs of mold or fungus on grains, cereals, oilseeds, and dried fruits

Appearance of Larvae

Another sign of foreign grain beetle presence is the appearance of their larvae in the infested area. These larvae are usually:

• Yellowish-white in color
• With a brown head
• Less than 1/8 inch long when mature²

Infested Food Products

Foreign grain beetles infest a variety of moldy food products. Keep an eye on:

• Cereals
• Grains
• Oilseeds
• Dried fruits

Prevention and Control Measures

Moisture Management and Ventilation

Proper moisture management is crucial in preventing foreign grain beetle infestations. Some ways to achieve this are:

• Using a dehumidifier to maintain relative humidity below 60%
• Properly ventilating spaces, especially in crawlspaces and basements
• Fixing leaks and addressing water intrusion promptly

For example, in a new home constructed during the rainy season, it’s essential to take measures to prevent excess moisture buildup.

Sanitation and Cleanliness

Maintaining cleanliness is an effective way to prevent foreign grain beetles. Key steps include:

• Regularly inspecting food products for pests
• Storing foods in sealed containers
• Discarding infested items in sealed plastic bags
• Cleaning up spills and crumbs immediately
• Vacuuming regularly to remove beetles and their food sources

Chemical and Non-Chemical Treatments

When it comes to treating foreign grain beetle infestations, both chemical and non-chemical options are available. Below is a comparison of some common methods:

Insecticides should be used as a last resort, and it is advisable to consult a pest management professional before application. Non-chemical options like desiccant dust and pheromone traps can be used for minor infestations.

By following these prevention and control measures, it’s possible to keep foreign grain beetles at bay and protect your property from infestations.

Comparison with Other Beetles

Sawtoothed Grain Beetle

The Sawtoothed Grain Beetle (Oryzaephilus surinamensis) is often found infesting stored food products. It is a small, narrow and flat beetle that is dark brown in color.

• Feeding: These beetles feed on a wide range of products such as cereals, dried fruits, nuts, and spices.
• Damage: They can cause considerable damage to food products, making them unsuitable for consumption.
• Excess moisture: Sawtoothed grain beetles thrive in environments with excess moisture.

Flour Beetle

Flour Beetles include two species: the Confused Flour Beetle (Tribolium confusum) and the Red Flour Beetle (Tribolium castaneum). Both of these beetles infest stored food products, especially flour.

• Nuisance: Although they don’t bite or sting, they can cause significant damage to stored food products.
• Spices: Their presence can alter the taste of spices and baked goods.
• Biology & Reproduction: These beetles reproduce quickly and adapt to various environments.

Flour Beetle description provides more information on their appearance and behavior.

Fungus Beetle

Fungus Beetle, like the Foreign Grain Beetle (Ahasverus advena), primarily feeds on molds and fungi growing on damp grain, grain products, and other materials.

• Dead insects: It can be found in areas where dead insects are present, as they also feed on them.

Comparison Table

These comparisons provide a brief overview of the differences and similarities between the foreign grain beetle and other common beetles found infesting stored food products.

Other Interesting Facts and Behavior

Migration and Strong Fliers

Foreign grain beetles are known to be strong fliers, which allows them to travel significant distances and, as a result, can infest new homes or older ones. These beetles can easily be confused with fruit flies or gnats due to their small size and strong flying abilities.

Foreign Grain Beetles in Older Homes

Older homes may experience a foreign grain beetle infestation if they provide suitable conditions, such as:

• Damp environments, like humid bathrooms
• Presence of mold or fungi
• Stored products with high moisture content

Foreign grain beetles are attracted to older homes because they often have damp spaces like wall voids and crawlspaces where mold can grow on building materials, which is their primary food source.

Quick Facts:

• Family: Silvanidae
• Body color: Reddish-brown
• Pronotum: Two peg-like projections behind the head
• Larva stage: Pupa
• Habitat: Stored products, damp spaces, and moldy grain

Homeowners can prevent and control foreign grain beetle infestations by maintaining proper moisture levels, conducting regular pest control inspections, and storing products in sealed containers.

To sum it up, foreign grain beetles are small and robust fliers that can migrate to new or older homes, and they can be confused with fruit flies. They are attracted to humid environments and moldy materials, which makes older homes with damp spaces and stored products more prone to an infestation.

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 – Probably NOT Foreign Grain Beetle

Please help me identify this bug
Location:  illinois
September 21, 2010 10:42 pm
finding many of these little bugs all over my house. This is the first year this has happened. Please help me identify this bug, thinking it some sort of beetle. Also, looking for best solution to getting rid of these little guys.
thanks for your help. sorry for poor quality pics.
Signature:  beetle help identify

We had a bit of trouble with this one, and we are not certain that our identification is correct, but it is possible that you have an infestation of Foreign Grain Beetles, Ahasverus advena, also called the New House Bug because it is”common in homes (esp. newly built) and grain storage facilities” according to BugGuide, which also indicates it feeds on “Molds and fungi growing on damp grain, grain products, and other materials.”  Sadly, we realized our identification was incorrect the minute we found the University of Arkansas Arthropod Museum website which has a nice page devoted to the Foreign Grain Beetle and which indicates:  “They have two conspicuous and diagnostic round lobes on the prothorax right behind the eyes.”  Those lobes are missing in your beetle, so alas, we have drawn a blank on the species identification unless the lobes are just not visible because of your camera angle.  There are a multitude of insects that will infest stored foods, and we believe this must be one of them.  If the actual identity is critical for you, and if none of our readers come to our rescue here, we suggest you begin scouring the internet for potential Grain Beetles like those profiled on the Grain Beetles page of the Pest Products website.

Letter 2 – Possibly Sawtooth Grain Beetle

Found in my carpet…
Location: Toronto, Canada
February 2, 2012 3:13 pm
Hi,
I am having a heck of a time identifying these critters I found in my carpet. Can you help? I have uploaded a couple pics, it is not very big, and dosnt look like a roach to me… I need to know what they are to get rid of them and to know if there is any health risks.
Thanks a bunch!
Signature: Want-to-get-rid-of-them 🙂

Dear Wtgrot,
It is difficult to be certain because the resolution on your image is so poor and when the underexposure is corrected, there is a great deal of visual noise, but this might be a Sawtooth Grain Beetle, Oryzaephilus surinamensis, see BugGuide.  If we are correct, you might want to check stored grain in the pantry, or possibly even large quantities of bird seed or pet food.

Letter 3 – Possibly Sawtooth Grain Beetles

Subject: What’s that bug
Location: New Brunswick
February 3, 2016 12:06 pm
Hi I have these little bugs infesting my apartment. They are in my pantry, my floor, my closet, and around my cats food. I’m so annoyed by them and want to get rid of them.
Signature: Helppp please

These sure look like Sawtooth Grain Beetles, Oryzaephilus surinamensis, to us, though there is not enough detail to be certain.  They might also be the closely related Merchant Grain Beetle, Oryzaephilus mercator, and according to BugGuide:  “Adults and larvae feed primarily on cereal products, particularly oatmeal, bran, shelled sunflower seeds, rolled oats, and brown rice; usually associated with oilseeds and less with cereal grains and in most regions damages processed cereals, especially those with high oil content; also feeds on seed-borne fungi”  You may compare your image to the images posted to BugGuide.

Letter 4 – Sawtooth Grain Beetle

Subject: Leaving Las Vegas
Location: Las Vegas
April 10, 2016 9:49 am
We found 3 of these bugs in our suitcase as we were leaving Las Vegas this weekend. Please help us identify.
Signature: Matt

Dear Matt,
We believe this is a Sawtooth Grain Beetle, Oryzaephilus surinamensis, one of numerous species of small, brown beetles that infest stored foods.  Compare your individual to this BugGuide image.  According to BugGuide, it is a “serious pest of stored grain; presence in household products is incidental and causes little concern; does not attack unbroken grain, but uses small lesions on the surface to gain entrance.”

Looks like a perfect match.  Thank you so much for the quick response.

Letter 5 – Sawtooth Grain Beetle

Subject:  Big found in kitchen cabinets
Geographic location of the bug:  New York
Date: 11/10/2018
Time: 06:30 PM EDT
Your letter to the bugman:  Hello,
For the last couple of weeks I have had what I thought was an ant problem in my kitchen cabinets but now I am questions the type of insect
How you want your letter signed:  Ellie

Dear Ellie,
This is a Sawtooth Grain Beetle, one of the many species of beetles that infest stored foods.  According to BugGuide:  “serious pest of stored grain; presence in household products is incidental and causes little concern.” 

Letter 6 – Sawtooth Grain Beetle we believe

Subject: What is this?
Location: NYC
November 19, 2016 7:01 pm
Found these in a shopping bag when I came home from the store. What type of bug is this?
Signature: Nicole

Dear Nicole,
This looks like a Sawtooth Grain Beetle to us.  It is a species that infests stored foods, so bringing it home from a grocery store makes perfect sense.