Do Grain Beetles Bite? Uncovering the Truth

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Grain beetles are commonly found in households, particularly in stored food products such as grains, cereals, and pasta. Two prevalent grain beetle species are the sawtoothed grain beetle (Oryzaephilus surinamensis) and the merchant grain beetle (Oryzaephilus mercator), which have similar appearances and habits. These tiny insects, approximately 1/10 inch in length, are often mistaken for harmful pests due to their presence in food items.

Despite the nuisance they can cause, grain beetles do not bite or pose a significant threat to humans. They are mainly considered pests because they can infest and contaminate stored food products. It’s essential to manage grain beetle infestations through proper sanitation and storage practices to avoid damage to food items in homes and commercial settings.

An example of an unrelated but often confused beetle is the foreign grain beetle, which does not typically infest food products in homes unless they are old and moldy. This distinction highlights the importance of identifying the correct beetle species for effective pest management strategies.

Grain Beetles and Their Common Types

Grain beetles are pests that infest stored grains and processed food products. There are two common types of grain beetles: sawtoothed grain beetles (Oryzaephilus surinamensis) and merchant grain beetles.

Sawtoothed Grain Beetle

The sawtoothed grain beetle is a small, brown beetle with a flattened body, measuring 1/10-1/8 inch long. Its striking feature is the six saw-like teeth on the first body segment behind its head. Some characteristics include:

  • Adult beetles do not fly
  • Not attracted to light
  • Larvae are yellowish-white, with brown heads, and less than 1/8 inch long when mature

These beetles feed on various food items, such as:

  • Cereal products
  • Dried fruits
  • Nuts
  • Pet food

Merchant Grain Beetle

Merchant grain beetles are similar to sawtoothed grain beetles in appearance and size, but they have some differences, which are summarized in the comparison table below:

Characteristic Sawtoothed Grain Beetle Merchant Grain Beetle
Flight Cannot fly Capable of flight
Food preference Cereals, nuts, dried fruits Cereals, seeds

While both beetles can infest stored food products, they can be managed by practicing proper sanitation and using sealed food containers to prevent infestations.

Identification and Appearance

Body Characteristics

The adult grain beetles, specifically the saw-toothed grain beetle (Oryzaephilus surinamensis), have a flattened body with a brown color. Some features of their appearance include:

  • Small size
  • Six saw-like teeth on the first segment behind the head
  • Not attracted to light
  • Cannot fly

The larvae of these beetles are usually yellowish-white, featuring a brown head1.

Length

Saw-toothed grain beetles are quite tiny, measuring around 1/10-1/8 inch long2. Meanwhile, their larvae are smaller, growing to less than 1/8 inch when they reach maturity3.

Projections

The name “sawtoothed” comes from the distinct saw-like projections found on the pronotum (the first segment behind the head) of these beetles. These projections, or teeth, are curved and wide in sawtoothed grain beetles4.

Diet and Infestation

Infested Foods

Grain beetles primarily feed on:

  • Cereals
  • Pasta
  • Dried fruits
  • Nuts
  • Pet food

They can also infest products such as flour, bread, sugar, chocolates, and yeast1. The adult beetles are around 1/10 inch long, with flattened bodies well-adapted to crawling into tiny crevices2. The larvae are usually yellowish-white with a brown head and less than 1/8 inch long when mature3.

Infestation of Stored Food Products

Infestation occurs most commonly in foods stored for long periods, especially if containers are replenished without first being emptied and cleaned4. For example, cereals and flours are more likely to become infested due to prolonged storage.

Prevention tips:

  • Store foods in airtight containers.
  • Regularly clean pantry shelves and storage areas.
  • Dispose of infested products to prevent beetles from spreading.

Tedious as it may be, dealing with grain beetles is necessary in order to maintain the quality and safety of your stored food products.

Life Cycle and Reproduction

Eggs

Saw-toothed grain beetles lay eggs individually or in small batches near a food supply. Adult female beetles lay their eggs around their preferred food sources, which can include grains, cereals, and pasta, among others. An example of this behavior can be seen in the tendency of the female beetle to lay her eggs on the surfaces of stored grains, hence the name “grain beetles.”

Larvae and Cocoons

Saw-toothed grain beetle larvae start off as [yellowish-white] (https://extension.entm.purdue.edu/publications/E-228/E-228.html) in color with a brown head. They undergo several developmental stages before reaching the cocoon stage. The larvae feed on the same food sources as the adults, further harming the stored products.

Generations and Female Beetle

Saw-toothed grain beetles can have [six generations per year] (https://extension.umaine.edu/ipm/ipddl/publications/5034e/) under normal conditions, making their population growth quite rapid. Female beetles are an essential part of this growth, contributing to the reproduction and expansion of the beetle population. Their high reproductive rate highlights the importance of controlling their population, especially in stored food environments.

A comparison of saw-toothed and merchant grain beetles:

Feature Saw-toothed grain beetle Merchant grain beetle
Generations per year 6 Fewer, shorter lifecycles
Egg-laying capacity Higher Lower
Preferred food sources Grains, cereals, pasta Similar
Control methods Sanitation, temperature management Similar

Prevention and Control Methods

Inspection and Sanitation

  • Conduct regular inspections of your pantry and other stored grain areas.
  • Dispose of any infested food immediately.
  • Store grains in plastic containers with tight lids.
  • Seal cracks and crevices to prevent beetle entry.
  • Ensure proper sanitation and cleanliness.

For example, a weekly inspection of your pantry can help you identify any signs of grain beetles early and take action accordingly.

Treatment and Cleaning

  • Use a vacuum to remove beetles and their debris from surfaces.
  • Place infested grains in light to kill larvae and eggs.
  • Apply an appropriate treatment advised by an entomologist.
  • Regularly clean and sanitize your pantry.

It is important to choose the right treatment based on the type of grain beetle you are dealing with. The merchant grain beetle may require a different approach compared to other species.

Here’s a comparison table of two common approaches:

Method Pros Cons
Vacuum cleaning Non-toxic, easy to perform May not remove all eggs and larvae
Light exposure Environmentally friendly Can be time-consuming, less effective for large infestations

By following these prevention and control methods, you can effectively manage the presence of grain beetles and protect your stored grains.

Bug Control Recommendation Tool

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Special Considerations

Grain Storage Facilities

Grain beetles, such as the saw-toothed grain beetle and the foreign grain beetle, can infest grain storage facilities. To prevent infestations:

  • Inspect grain regularly with a magnifying glass
  • Keep storage areas clean
  • Rotate stored food products regularly

Ventilation

Proper ventilation is essential for preventing grain beetle infestations. Good air circulation:

  • Reduces moisture levels
  • Helps maintain lower temperatures
  • Deters beetle reproduction and growth

Insecticides

There are various insecticides available for controlling grain beetles:

  • Stryka: Specialized insecticide for beetles
    • Pro: Targeted control
    • Con: May require multiple applications
  • Tobacco-based insecticides: Natural alternatives
    • Pro: Environmentally friendly
    • Con: Risk of tobacco contamination
Insecticides Pros Cons
Stryka Targeted Multiple applications
Tobacco-based Environmentally friendly Tobacco contamination

In conclusion, employing proper storage methods, ventilation, and insecticides can help prevent and control grain beetle infestations. Always ensure to follow best practices when managing stored grain products.

Footnotes

  1. Saw-Toothed Grain Beetle | Home & Garden Information Center 2
  2. Grain Beetles – Texas A&M University 2
  3. SAWTOOTHED GRAIN BEETLE Oryzaephilus surinamensis (L.) 2
  4. State of Oregon: Insects – Identify an Insect 2

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 – Merchant Grain Beetles

 

Subject: is this a pantry beatle?
Location: NJ
September 24, 2012 8:56 pm
Hi,
About a year ago i found an infestation in my kitchen which i think came from a box of newly opened pasta.
I threw out most of the items on my counter along with all the bugs i found.
Every once in a while i would come accross a bug which i would then dispose of.
Recently i have noticed that my pantry (especially the places with chocolate has become infested. The only thing that truly seems to kill the buggers is crushing them with my finger or putting them in the freezer.
Based on other things i read on this website i believe that these may be pantry beatles. Can you tell if this is the case
Can you recemmond what might kill them? i have tried raid but have had limited success. Would bleach work?
Thanks
Signature: Ricki

Merchant Grain Beetles

Hi Ricki,
We believe these are Merchant Grain Beetles,
Oryzaephilus mercator, and while they are often found in stored foods in the pantry, they are actually classified with the Bark Beetles.  According to BugGuide:  “Adults and larvae feed primarily on cereal products, particularly oatmeal, bran, shelled sunflower seeds, rolled oats, and brown rice(3); 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.”  The best control is keeping a close watch on stored foods and disposing of anything that appears to be infested.

Merchant Grain Beetles

Letter 2 – Merchant Grain Beetle

 

Help Me Figure Out What This Is…
Hi,
My house has recently had an infestation of a bug that seems to really be a fan of grain. We’ve found it inside our sealed cereal boxes and also in packets of oatmeal. After putting all of our food in sealed containers the contagion seems to have died down, but now I’m finding some throughout our house. I took a number of digital pictures but this is the only one that came out pretty well. The bug resembles a very tiny ant except it obviously isn’t an ant. It is about 2 mm long. Hopefully you can identify it, I’ve searched many many sites.
Thanks!
Zach

Hi Zach,
It looks like you have a type of Merchant Grain Beetle, possibly Oryzaephilus mercator or the closely related Saw-toothed Grain Beetle, Oryzaephilus surinamensis. These are very small beetles that are elongated. According to Hogue: “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.”

Letter 3 – Merchant Grain Beetle

 

A Few More Things About my Bug/Fly/Beetle
November 4, 2009
My bugs have very distinct personalities. If they are fruit flies or drain flies, they don’t fly around fruit or the drain. They’re very lazy and just sit there. If I try to capture them, they do squirm away – but of course I’m faster. If they’re some kind of pantry beetle/saw tooth beetle, they don’t match the profile. I have yet to find them in food. Like a lunatic I’ve been going through every box, carton or bag, examing them and then throwing them out. I haven’t found these creatures in any food source. They now seem to take the occasionally holiday from the kitchen for an excursion the the dining room. There is no food or moisture in the dining room. I can’t figure out what they are afte other than a dark place to huddle. I may have get up in the middl e of the night with a miners cap to figure out what they are. Please save me this embarssment. It’s nearly halloween, so I think I’m safe from being reported to the asylum for wearing my bug tracking costume. People will think I dressed as an exterminator – I hope. All my food is now solely in the fridge. This is horrible.
Pest-ered Still and Exhausted
NE US- PA

Merchant Grain Beetle
Merchant Grain Beetle

Dear Pest-ered Still and Exhausted,
We are posting some old letters today, and we are not certain if you have eradicated your beetle infestation.  These are Sawtoothed Grain Beetles or Merchant Grain Beetles in the genus Oryzaephilus which is represented on BugGuide which states:  “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.”

Letter 4 – Merchant Grain Beetles or Sawtooth Grain Beetles

 

Mastic Beach beetles
I sent you some pictures of the tiny beetles we have last week but it was from an email account I’ve been having problems with. I haven’t seen them posted nor did I get a reply so I’m sending you them again from an email account I know works. I’ve been through all of the beetle and ant pages and nothing posted looks like these creatures. Photos are all of dead bugs, the live ones won’t pose for me: IMGA0981 – several on the handle of a plastic knife; IMGA0989 – best I could do for a closeup of the head area
Thanks for your help.
Jeff
nevermind searching
I found the bug on another site, it’s as follows: Sawtoothed Grain Beetle (Oryzaephilus surinamensis): The Sawtoothed grain beetle is another very common pantry pest. It does not feed on intact whole grains, but feeds on many processed food products such as breakfast food, bran, dried fruits, nuts, sugar, chocolate and macaroni. It is especially fond of oatmeal and birdseed. These flat beetles can even get into sealed boxes and packages of food. Adults are nearly 1/4-inch long, slender, brownish-red and active. Their name comes from the six saw-like teeth on either side of the thorax behind the head. After finding a potential food, the female lays white, shiny eggs that hatch into yellowish-white larvae. There can be as many as seven generations each year, but sawtoothed grain beetles often stop breeding in the winter, unless buildings are heated and moisture is sufficient. Adults are very long lived and remain active in the winter. The habits and traits are a perfect description and I think the source is the food we get for our parrot. Here’s the link to the other site and a copy of the photo. Between my closeup and the description I think I have a match.

Hi Jeff,
Thanks for the information, and sorry we have been slow, but we could literally spend 24 hours a day answering letters, which is impossible. There is another closely related species, the Merchant Grain Beetle, Oryzaephilus mercator, that looks very similar. According to Hogue: “Its distinguishing feature is a small swelling on the head behind the eye which is lacking in O. surinamensis.” Your closeup seems to indicate this swelling. We favor the Merchant Grain Beetle.

Authors

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    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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Tags: Grain Beetle

Related Posts

7 Comments. Leave new

  • If you place bay leaves around in your pantry the grain beetles will flee and never come back. You can by bay leaves in bulk at certain food chains or Richards Whole foods carry them.

    This was the only way I could get rid of the pesky things.

    Reply
  • I have found these little black grain looking beetles but they haven’t been in my pantry. I found them in an old backpack that wasn’t used for about two years, and found chocolate broke into a fine power from their eating it and also they were in an old vitamin c drop they had burrowed holes in it and were living happily inside. I cleaned it all out but I still see them around; in the bathroom, bedroom, kitchen. However they aren’t in any rice or grain of any type, not even cereal. Not sure where they’re coming from or if they’re an adapted version. I would like to get rid if them forever but not sure how. Please help.

    Reply
  • I have them too.
    They are basically growing!
    They get into everything!
    They started in a walk in closet in my bedroom and are just in things like .. a suitcase, or randomly in my bathtub, or sink in bathroom. I saw one in a candle o had in my kitchen. I’ve put around diatomaceous earth and I’ve seen it catch a few but nothing that I need to get all of them. I now saw two in my pillow! Help! I’m so clean and don’t see them feeding on anything …

    Reply
  • I have them too.
    They are basically growing!
    They get into everything!
    They started in a walk in closet in my bedroom and are just in things like .. a suitcase, or randomly in my bathtub, or sink in bathroom. I saw one in a candle o had in my kitchen. I’ve put around diatomaceous earth and I’ve seen it catch a few but nothing that I need to get all of them. I now saw two in my pillow! Help! I’m so clean and don’t see them feeding on anything …

    Reply
  • shannon callahan
    October 31, 2022 11:44 pm

    I’m thinking it might be what I’m finding in my bed, I find brown smeared stains with tiny brownies black tiny worm/insects .

    Reply

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