Acorn Weevil: All You Need to Know in a Nutshell

Acorn weevils are fascinating insects that feed primarily on acorns, as their name suggests. These fascinating beetles are brown in color and have a distinctive long, thin snout, which they use for boring into acorns to lay their eggs. They have a curved body, tapering towards both ends and grow up to about 3/8 inch long

What Is an Acorn Weevil?

The Acorn Weevil, or Curculio sp., is a small, brown beetle belonging to the order Coleoptera, the family Curculionidae, and the genus Curculio1. Key attributes of this insect include:
  • Length: About 3/8 inches2
  • Color: Brown
  • Distinctive characteristic: Long, thin snout

Life Cycle and Reproduction

Acorn Weevils undergo a complete life cycle, consisting of egg, larva, pupa, and adult stages. The female nut weevil lays her eggs inside developing acorns, hickory nuts, or other similar nuts, by boring tiny holes with her slender snout3. Once hatched, the pudgy, legless larvae feed on the nutmeats before boring their way out4. These larvae then drop to the ground and burrow into the soil to spend one to two years before pupating and emerging as adults5.

Geographical Distribution

As part of the Curculio genus, Acorn Weevils are found around the world. They are primarily found in regions where oak trees and other nut-producing trees grow in abundance. Specific species like Curculio glandium can be found in certain geographical areas, each with a preference for different types of nuts.

The Impact of Acorn Weevils on Trees

Oak Trees

Acorn weevils are insects notorious for infesting the acorns of oak trees. These weevils have long, slender snouts called rostrums. They come in the brownish color and varied patterns1. Female acorn weevils have longer rostrums compared to their male counterparts1. During their lifecycle, the adult weevil lays eggs inside green acorns4. After hatching, the larvae feed on the acorn’s interior, having a detrimental effect on the tree’s reproductive ability4. Once the acorns fall to the ground, the larvae emerge, burrow into the soil, and continue developing4. In oak trees, the impact of acorn weevils can cause:
  • Reduced seed production
  • Potential damage to tree health and growth
  • Disrupted food sources for wildlife species3

Hickory Nuts and Hickory Trees

While information regarding the direct impact of acorn weevils on hickory trees is scarce, nut weevils, in general, can affect hickory nuts. Nut weevil larvae are legless grubs that feed on the interior of nuts, much like acorn weevils2. The larvae of nut weevils have similar effects on hickory nuts and trees. These include:
  • Reduction in viable nut production
  • Disruption of nut-based food sources for wildlife
  • Compromised tree health and growth2
Comparison of Acorn and Nut Weevil Impact
Impact Acorn Weevils Nut Weevils
Seed production Reduced Reduced
Tree health Potential damage Potential damage
Wildlife food Disrupted Disrupted

Detecting Acorn Weevil Infestation

Acorn weevil infestations can be identified by observing the acorns themselves. Damaged acorns may have:
  • Holes: Small, perfectly round exit holes created by weevil larvae
  • Color: A faded or darker appearance, signaling internal damage
  • Mealy texture: The inside of the acorns might appear mealy and dark brown, a sign of insect activity
Table Showing The Differences Between Healthy And Infested Acorns
Healthy Acorn Infested Acorn
No holes Small, round holes
Vibrant color Faded/darker color
Solid texture Mealy, dark insides

Identifying Weevil Larvae and Grubs

The larvae of acorn weevils, also known as grubs, have distinct characteristics:
  • Size: Grow to about 3/8 inch long
  • Shape: Curved, tapering toward both ends, fatter in the middle
  • Color: Creamy white, with a brown head
For example, when opening an infested acorn, you might find a grub-like larva that has been feeding and causing damage. Comparison of Acorn Weevils and Chestnut Weevils: While adult acorn weevils are about 3/8 inches long with a long, thin rostrum, chestnut weevils are slightly larger, reaching up to 1/2 inch in length. Both types of weevils feature rostrums that they use to bore holes and lay their eggs in the nuts.
Feature Acorn Weevil Chestnut Weevil
Size 3/8 inch long Up to 1/2 inch long
Rostrum Long, thin rostrum Long, thin rostrum
Infested Nut Acorns Chestnuts
Larvae Appearance Creamy white with brown head Similar to acorn weevil larvae
Weevil larvae, regardless of the type, pupate in the ground before emerging as adults. Detecting an infestation early can help in preventing further damage to the acorns or other nuts.

Controlling Acorn Weevils

Cultural Practices

Acorn weevils can be managed through various cultural practices. One effective method is to collect acorns in the fall, as it helps reduce the number of larvae that survive during winter.

Insecticides and Pesticides

Using insecticides and pesticides can help control acorn weevil populations by targeting adults or larvae. Keep in mind that:
  • Some insecticides may have a negative impact on the taste of acorns.
  • Be cautious when using chemicals, as they can also affect other species, such as squirrels.

Natural Predators

Acorn weevils have natural predators that can help reduce their numbers. These include rodents, which are common in North America and Europe. Table showing the pros and cons of different acorn weevil control measures
Method Pros Cons
Cultural Environmentally friendly Time-consuming
Insecticides Effective in killing weevils Can affect taste and harm other species
Natural Predators No chemicals needed Reliance on other species

Acorn Weevil and Human Interaction

The Acorn Weevil (Curculioninae) is a small insect that can affect the quality of acorns collected during autumn for human consumption. They are considered a pest due to their larvae tunneling into acorns, rendering them useless. Here are some tips to consider when collecting acorns:
  • Collect acorns in September, before heavy rains or after the weevil has emerged
  • Discard acorns with tiny holes, indicating weevil presence
When it comes to managing Acorn and Nut Weevil populations, consider these methods:
  • Regularly clean up fallen acorns to reduce habitat for reproduction
  • Introduce natural predators, like birds and rodents, to the area

Effects on Wildlife and Ecosystems

Acorn Weevils can impact the ecosystems as they reduce food source for other wildlife. While collecting acorns, you might notice some of the following characteristics in infected acorns:
  • Acorns that feel lightweight due to tunneling
  • Tiny holes on the surface
Acorn Weevils can make it challenging to gather and store acorns for human consumption. Proper collection techniques, identification, and management methods can help mitigate the effects of these insects.

Conclusion

Acorn Weevils play a significant role in the ecosystems where oak trees and other nut-producing trees thrive. Their life cycle, reproductive habits, and impact on tree health and seed production highlight their ecological importance. Understanding the signs of infestation and implementing control measures, such as cultural practices and natural predators, can help mitigate their effects. By managing Acorn Weevil populations, you can maintain the balance of wildlife food sources.

Footnotes

  1. Horticulture and Home Pest News 2 3
  2. Acorn Weevil | NC State Extension Publications 2 3
  3. Nut Weevils (Acorn Weevils) | Missouri Department of Conservation 2
  4. University of Kentucky Entomology for Kids 2 3 4
  5. Acorn Weevil | NC State Extension Publications

Acorn Weevils – Letters from Readers

The Acorn Weevil is one of the most famous insects that our readers talk about and ask to know about. Over the last two decades, we have received dozens of emails from our readers asking us to identify this beautiful insect.

We have reproduced some of the best ones with some beautiful images for you to have a look.

Letter 1 – Acorn Weevils Mating

mating acorn weevils HI BUGMAN!! I love your site!! It’s helped me identify lots of insects and has only helped my already huge interest in bugs. I have been having a problem with acorn weevils on my pin oak tree in Columbia MO… so they pose a threat to the tree? attached is a picture of two of them mating. THANKS!! Andrew M. Hi Andrew, Thanks for sending a new species to us. The Acorn Weevil, Curculio glandium, can be quickly distinguished by the elongated snout or rostrum. We have located information that the Acorn Weevil does not pose a threat to the oak tree itself as both adults and larvae feed on the acorns. We apologize for not having the ability to respond to every letter you have written to us, and if there is anything that is either new to our site or a pressing matter for you, please resend those letters and images.

Letter 2 – Acorn Weevil

Kiwi-like bug Hello, My name is Matthew Frias, I am a 16 year old high school senior. I would like to ask for your help with identifying a strange bug. Today, I came across a strange looking bug that had a striking resemblance to the kiwi bird (well, to me at least) I have never seen this bug before in my life. I found this bug sitting on my nightstand in my room. It walks very slowly and has the ability to fly. The long apendage coming from its head seem like it is used to feed on sugar food (flowers perhaps?) I tested this by giving it a bit of sugar-water. It doesn’t seem to be dangerous since i’ve picked it up before. Also, the apendage coming out of its head seems to have two antenae attatched to it. They come out a little less than half-way from the face. I have attached a sample picture of the bug. If you need more samples I have other pictures at different angles. Yet I feel this is one of the best angles I could get with my camera. Thank you very much. Matthew Frias, Alhambra CA Hi Matthew, This is an Acorn Weevil in the genus Curculio. The California Acorn Weevil is Curculio uniformis, but we cannot quickly locate an image nor the range. That species is still our best bet.

Letter 3 – Acorn Weevil

Acorn Weevil pics for you plus my gratitude Dear Bugman, I found you last week when I wanted to know what beautiful bug was crawling on my kitchen bowl. Thanks to you I discovered it was an Assasin Bug(pselliopus barberi) and a whole new world was opened up to me. I had never even heard of an Assasin bug before. Now I am a little addicted to finding bugs in my yard and trying to identify them. I guess I love the challenge, and it’s terribly fun to find a match and put a name with the buggy face. I’ve been using your site and the BugGuide. Thank you so much for a wonderful and facinating resource for the bug illiterate. My kids love it, too. We are working on creating science journals this year, and our bug finds with proper identification are a great addition! I thought you might like to have some pictures of our Acorn Weevil. I noticed the one you have is blurry. Also, I thought this was a pretty picture of a Monarch Caterpillar. These were all taken in my yard in Jefferson City, Missouri. I would like to send other pictures just for fun, but only if you want them. I know you get so many. With much gratitude and admiration, Rachelle Gilbert Hi Rachelle, Thanks so much for your Acorn Weevil photo. We are linking to an interesting website about Acorn Weevils in the genus Curculio.

Letter 4 – Acorn Weevil

Ugly Bug Fri, Jan 23, 2009 at 5:59 AM What kind of bug is this? Is it dangerous? I found it indoors about a week ago in our living room, on our couch. Mr. oklahoma city, ok
Acorn Weevil
Acorn Weevil
Hi Mr, This is an Acorn Weevil in the genus Curculio which can be verified on BugGuide. The snout is quite distinctive for Nut Weevils and Acorn Weevils.

Letter 5 – Nut or Acorn Weevil, we think

What is this thing? October 25, 2009 I found this bug on the edge of my fishtank. It is now October 25th. Tree C. Central Florida
Nut or Acorn Weevil, we believe
Nut or Acorn Weevil, we believe
Hi Tree C., This is a Weevil, a member of the largest family of Beetles.  Often exact identification from a photo is impossible.  That said, we believe this is a Nut Weevil or Acorn Weevil in the Tribe Curculionini.  There are several images that look similar on BugGuide, but they are not identified to the species level.
Nut Weevil or Acorn Weevil, probably
Nut Weevil or Acorn Weevil, probably

Letter 6 – Acorn Weevil

beetle thing with long beak Location:  Farmingdale, Long Island, New York August 26, 2010 12:54 am Dear Mr. Bugman, I’ve been browsing your site and haven’t really found anything close to this little guy I found today. I work at an airport in New York, and I found him while I was pumping fuel into my fuel truck. It looks kinda like a beetle, but it has this really strange beak. The beak is thin and about the length of one of its legs. And it looks like it has two antennae (?) protruding from the beak. The insect itself is about a centimeter long, I would say. This is the strangest insect I’ve seen in a while. I really hope you get to this one because I really want to know what it is! Thanks, Trevor
Acorn Weevil
Hi Trevor, This interesting beetle is an Acorn Weevil in the genus Curculio.  According to BugGuide:  “Female uses her long snout for boring into nuts/acorns, and deposits eggs there. Larvae feed inside the acorn/nut and emerges to pupate in the soil.

Letter 7 – Nut or Acorn Weevil

What on earth is this?? Location: Bensalem, PA March 8, 2012 9:13 am A friend of mine took a picture of this bug while he was at an ATM in Bensalem, PA. It was on the ATM itself. This was taken either at the end of Feruary or the beginning of March. Signature: Bill O’Neill
Acorn Weevil
Dear Bill, This long nosed creature is a Nut or Acorn Weevil in the genus Curculio.  According to BugGuide:  “Female uses her long snout for boring into nuts/acorns, and deposits eggs there. Larvae feed inside the acorn/nut and emerges to pupate in the soil.”  

Letter 8 – Acorn Weevil from Japan

Subject: Help a Bugger Out Location: Tosa Peninsula, Kochi, Shikoku, Japan May 15, 2014 6:17 am Hello bugman! Me and my boyfriend have been travelling in Japan now for 7 months. We came here originally for the birds but the huge variety of strange, colourful and giant insects have been stealing the show a bit. This guy flew down off a tree, looking closely at its face we decided it was the funniest bug we had seen all trip, so that seems like a good place to start. I would like to send more if that’s okay? Signature: Ellie
Acorn Weevil
Acorn Weevil
Hi Ellie, This is an Acorn Weevil in the genus Curculio, but our quick research did not determine which species are found in Japan.  You can find information on BugGuide regarding North American species that might be helpful for you.

Letter 9 – Acorn Weevil

Subject: What the heck is this? Location: Queens new york September 9, 2015 12:14 pm Help, this thing was on the wall, I live in Oakland gardens Queens NY and I found it. It has one long nostril or idk what that is. It has six legs and little suckered freaked me out when I learned it could fly! I don’t want to kill it if it’s not harmful. I’d much rather let it go, but I need to know if it’s harmful or not. Please get back to me soon! Signature: Freaked out human
Acorn Weevil
Acorn Weevil
Dear Freaked out human, Does the Oakland Gardens have many of its namesake oak trees nearby?  This is an Acorn Weevil and we believe it inadvertently entered your home.

Letter 10 – Acorn Weevil

Subject: I can’t identify this bug Location: Georgia October 5, 2015 9:53 pm This bug was in my friend’s hair and I must know what it is. Is it some type of weevil? Signature: KDD
Acorn Weevil
Acorn Weevil
Dear KDD, This is indeed an Acorn Weevil or Nut Weevil in the genus Curculio.  Finding it in your friend’s hair seems purely coincidental.  According to BugGuide:  “Female uses her long snout for boring into nuts/acorns, and deposits eggs there. Larvae feed inside the acorn/nut and emerge to pupate in the soil.”

Letter 11 – Acorn Weevil

Subject:  Never saw this one before Geographic location of the bug:  Oklahoma City Date: 09/29/2017 Time: 07:45 AM EDT There were several of these in a Porta pot for about 5 days.  They can fly too. How you want your letter signed:  Jeff
Acorn Weevil
Dear Jeff, This is an Acorn Weevil or Nut Weevil in the genus Curculio.  According to BugGuide:  “Long slender beak; body robust. In some species, female snout may be longer than the body (never in males).”

Letter 12 – Acorn Weevil

Subject:  Really weird and really scared Geographic location of the bug:  sherman, texas Date: 11/07/2018 Time: 08:30 AM EDT Your letter to the bugman:  This thing landed on my arm in my office and i have no idea what it is. I didn’t feel any bite, all I felt was it land on my arm, and i brushed it off immediately. I just need it identified to know if I’m in danger of a parasite, infection, virus or otherwise transmittable illness. It has what I can only assume to be some form of proboscis and an empty white container on its “abdomen” with a grey/black and brown color and a somewhat fuzzy appearance. It also had a triangle-like shape when viewed top down. How you want your letter signed:  Gerald
Acorn Weevil
Dear Gerald, This appears to be a very dead Acorn Weevil or Nut Weevil.  You need not fear “danger of a parasite, infection, virus or otherwise transmittable illness” from a harmless Acorn Weevil.

Authors

    by
  • Bugman

    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.

  • 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.

3 thoughts on “Acorn Weevil: All You Need to Know in a Nutshell”

  1. acorn-weevil , are they harmful to humans. I found one in my bedroom? Pls help , is there something I can do to prevent them?

    Reply

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