Oak Gall: All You Need to Know for Amazing Remedies and Crafts

Oak galls are fascinating growths that can be found on oak trees, caused by various organisms such as insects, mites, bacteria, fungi, or nematodes. These abnormal swellings of plant tissue typically occur on leaves and twigs, with the majority being formed by the egg-laying and feeding activities of insects and mites. These organisms produce chemicals that cause the affected plant cells to swell, leading to the formation of galls.

There are many different types of oak galls, each presenting unique characteristics. For instance, the horned oak gall is a woody growth about the size of a golf ball, with distinctive horns protruding from its surface. This gall is caused by a tiny wasp called Callirhytis comigera. Another example is the woolly oak gall, which has a fuzzy appearance and is also formed by the activity of wasp larvae.

While most galls don’t cause severe harm to the oak trees, some, like the gouty oak gall and horned oak gall, can lead to branch girdling or drooping due to the weight of the growths. In cases of heavy infestations, they may disfigure the tree, but it’s interesting to note that oak trees are highly resilient and can still live for many years even with these unique growths present.

Understanding Oak Galls

Concept and Formation

Oak galls are growths that develop on oak trees due to the feeding and egg-laying activity of certain insects, such as gall wasps (Cynipidae family). When these insects lay their eggs on leaves, stems, or buds of an oak tree, chemicals from the larvae interact with the plant tissues, leading to abnormal growths.

Common Types of Oak Galls

There are many types of oak galls, but two important ones are:

  1. Gouty Oak Gall: Appears as large, woody growths on oak tree twigs and branches. They can grow over 2 inches in diameter, sometimes causing branches to droop due to their heavy weight. Gouty oak galls are primarily found on pin, scrub, black, blackjack, and water oaks. (source)

  2. Horned Oak Gall: This golf ball-sized woody growth is also found on oak twigs, but it is characterized by horn-like protrusions on its surface. The main cause is a tiny wasp (Callirhytis comigera). While light infestations typically don’t harm pin oaks, severe infestations can lead to disfigurement and reduced tree health. (source)

Comparison of Gouty Oak Gall and Horned Oak Gall:

Feature Gouty Oak Gall Horned Oak Gall
Size Over 2 inches Golf ball-sized
Surface Smooth Horned
Impact Branch drooping Disfigurement
  • Features of Oak Galls:

    • Abnormal growths on oak trees
    • Caused by insect activity (mainly gall wasps)
    • Can appear on leaves, stems, or buds
    • Chemical interaction between larvae and plant tissues
  • Characteristics of Oak Galls:

    • Vary in size, shape, and color
    • Some are more harmful to oak trees than others
    • Often unsightly and may affect the aesthetics of the tree

Remember that there are multiple types of oak galls, and their impact on oak trees can range from minimal to severe. Always consult a professional arborist if you suspect a severe oak gall infestation.

Gall Wasps and Their Role

Life Cycle

Gall wasps, or cynipid gall wasps, have a unique life cycle, where they alternate between two types of galls. In spring, adult wasps emerge from woody stem galls, such as the horned or gouty oak galls, and lay their eggs in the swelling buds of the host tree. Larvae hatch, and wasps develop in small, blister-like leaf galls during the first generation.

Fall brings the second generation. Here, the wasps switch back to creating woody stem galls and the cycle repeats. Repeated infestations can cause stress to the host tree.

Reproduction and Mating

Gall wasps, like the oak apple gall wasp, exhibit diverse reproductive strategies. Some gall wasp species reproduce asexually, where the female does not require a mate to lay eggs. Other species need to mate before laying eggs in leaves and twigs.

Comparison table:

Gall Wasp Life Cycle Reproduction & Mating
Alternating between leaf and stem galls Some species reproduce asexually
Spring: adult emerges, lays eggs in buds Others require mating before egg-laying
Fall: switch to woody stem galls Females lay eggs in leaves and twigs

Characteristics of gall wasps:

  • Short life cycle
  • Diverse reproductive strategies
  • Can cause tree stress with repeated infestations

Examples of gall wasps:

  • Horned oak gall wasp
  • Gouty oak gall wasp
  • Oak apple gall wasp

While gall wasps play a critical role in the formation of oak gall, understanding their life cycle, reproduction, and mating habits can help manage their potential negative impact on host trees.

Impact on Oak Trees

Physical Symptoms

Oak galls are growths on oak trees caused by various organisms such as mites, bacteria, and cynipid wasps. These gall makers use oak trees as hosts for nourishment and development. Galls can cause symptoms like:

  • Foliage distortion
  • Twig or branch swelling

For example, woolly oak galls are caused by a small wasp and look fuzzy on oak tree foliage.

Long Term Effects

While galls can be unsightly, most oak gall types have minimal impact on the health and vigor of oak trees. Red oaks in North America, for example, can have leaf pockets caused by a midge species without significant long-term damage.

However, severe infestations may require intervention like pruning. An arborist should be consulted if there is concern for the tree’s health. Oak wilt, caused by the fungus Ceratocystis fagacearum, is a separate issue that can cause severe damage; fortunately, it is not known to exist in most areas of Maryland.

Comparison of Oak Gall Symptoms and Oak Wilt Symptoms:

Symptom Oak Gall Oak Wilt
Affected Tree Parts Foliage, twigs, branches Tree’s vascular system
Cause Mites, bacteria, cynipid wasps Fungal pathogen, Ceratocystis fagacearum
Impact on Tree Health Generally minimal Severe vascular damage

In summary, oak galls may cause physical symptoms but often do not pose a significant threat to the long-term health of oak trees.

Prevention and Control Measures

Homeowner’s Guide

To prevent oak galls, one method is to maintain tree health. This includes:

  • Regular watering
  • Proper pruning
  • Avoiding injuries to the tree

For existing galls, like the jumping oak gall and horned oak gall, remove and destroy fallen leaves to prevent wasps from pupating. Treating oak galls with water sprays may help, but it’s not always effective.

Insecticides can be a solution, although it’s challenging to reach insects when they’re inside galls. Avoid using chemicals unless absolutely necessary, and always consult a professional for guidance. Keep your home safe by being cautious with insecticide use.

Professional Care

Consulting entomologists or botanists may assist in identifying and managing oak gall issues. Professionals can help identify gall types, such as jumping oak gall or horned oak gall, and recommend appropriate solutions and treatments.

Here’s a comparison table of some oak gall types and their specific wasp species:

Oak Gall Type Wasp Species
Oak Apple Gall Wasp Biorhiza pallida
Jumping Oak Gall Neuroterus saltatorius
Horned Oak Gall Callirhytis comigera

Professionals can also help in dealing with tree species that are more susceptible to oak galls. They can assist in choosing the right tree species or provide recommendations on how to protect your oak tree host.

Overall, managing oak galls requires a combination of preventative measures, biological controls, and possibly chemical treatments. Working with professionals and understanding the specific oak gall type and appropriate control measures can lead to successful prevention and management.

Scientific Perspectives and Research

Oak galls are interesting phenomena in the natural world. They’re caused by the interaction between oak trees and cynipid wasps. The wasps lay their eggs on oak leaves, and the tree responds by forming a gall, which provides a home for the developing wasp larvae.

In horticulture, oak galls might be seen as a problem, especially for pin oak trees, commonly found in Missouri. The galls can be unsightly, and in severe cases, they can also stunt the tree growth or canopy. However, they’re not necessarily harmful to the tree itself.

Some beneficial insects, like parasitic wasps, use galls for their lifecycle. These insects can help control other pests, providing a natural form of pest control in horticulture.

Oak galls come in various sizes and types. For example, some might look like brown balls, while others resemble wool or cotton. The galls’ diameter can vary significantly, with some galls being tiny, and others growing quite large.

Fungi play a role in spreading oak galls. Spores from the fungus land on the bark of the tree, find an acorn, and infect it, causing the gall to form. If the gall becomes large enough, the infection can spread throughout the tree.

Some interesting features of oak galls include:

  • Differing appearances: brown balls, wool-like, or cotton-like structures
  • Varying sizes: from tiny to several inches in diameter
  • Hosts for beneficial insects: parasitic wasps

When comparing oak galls caused by cynipid wasps and those caused by fungi, some noticeable differences can be observed:

Characteristics Cynipid Wasp-induced Fungal
Formation Eggs laid on leaves Fungal spores infect acorns
Impact on oak tree Usually harmless Can be harmful if infection spreads
Beneficial insect usage Yes (parasitic wasps) No

In conclusion, oak galls are a fascinating part of nature with various appearances and causes. They can host beneficial insects and are generally harmless to affected trees, but a widespread fungal infection can pose risks.

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 – Oak Leaf Gall

 

Insect egg?
Location: Arkansas
March 19, 2011 9:01 pm
Bugman–we were hiking in west/central Arkansas in the Ouachita mountains and found this round orange ball with red spots on a leaf on the ground. It was about 3/4 of an inch in diameter. It was mid-March in a mixed deciduous/pine forest. What is it?
Signature: Joyce

Oak Leaf Gall

Dear Joyce,
This is theoretically not an insect egg, but it was produced because of the laying of an insect egg.  This is a Gall.  Galls are growths produced on plants, usually because of an insect or mite, though fungus and other causes may produce gall-like structures.  This is probably the result of a Gall Wasp in the family Cynipidae.  The Gall Wasp lays an egg, and when the egg hatches, the larva releases an enzyme that causes the Gall to grow.  The Gall Wasp Larva then feeds on the tissue in the Gall.  Galls do not harm the plants.  Here is a similar photo on BugGuide, and one on Wikimedia.

Letter 2 – Oak Gall

 

Subject:  Is this an insect sac?
Geographic location of the bug:  Southeast MO
Date: 10/07/2017
Time: 08:10 PM EDT
Found Oct 7, 2017 bear Lampe, MO.
How you want your letter signed:  PJ

Oak Gall

Dear PJ,
This is a Oak Gall, probably caused by a Gall Wasp in the family Cynipidae.  According to Henderson State University:  “Galls are abnormal, vegetative growths that are usually formed as a response by plants to the action of fungus, mites, or insects such as wasps, aphids, and true bugs. Galls can be formed in the leaves, petioles (stem) of leaves, twigs, buds, or on the roots.”  More information on Galls can be found on Arborilogical.  Your Gall looks similar, but distinctly different than the Eastern Speckled Oak Gall pictured on ISA Texas.

Letter 3 – Oak Apple Galls

 

unusual oak galls?
Hi,
First, I love your site! These odd-looking galls appeared on some oak trees in my yard last year and they’re back this year. I can’t seem to identify them anywhere on the internet. I suspect they are wasps of some kind and don’t want to eliminate them if they’re harmless. My dog, a golden retriever, actually ate a few them today! GROSS! I assume since the squirrels eat them they must not be toxic. (?) Thanks in advance for any help in identifying what kind of creature is in there…
a bug lover

Hi Bug Lover,
We believe these are Oak Apple Galls, benign leaf galls produced by the Gall Wasp, Amphibolips confluenta, a “very small and dark cynipid wasps with an oval, compressed abdomen” according to a website we located. Another website indicates that several wasps produce Oak Apple Galls, also known as King Charles’ Apple. One species mentioned is Biorhiza pallida.

Letter 4 – Oak Apple or Oak Gall

 

Insect egg ball
July 31, 2009
Hi,
I keep finding these egg balls under an oak tree in my yard. Can you tell me what comes out of these? (The second picture shows their exits.) The wall material is paper thin and very brittle. They are about the size of a golf ball, beige, and bumpy.
Thank you.
Todd Shinn
Salisbury, NC

Oak Gall
Oak Gall

Hi Todd,
This is the Gall or Oak Apple formed by some species of Gall Wasp, a tiny wasp in the family Cynipidae.  The larval Gall Wasp creates the Gall as part of its growth process and the Galls do not harm the trees.
There are numerous species and according to BugGuide: Many different cynipid wasps form large, spherical galls on oak leaves, some of which are called “oak apples.” As with most galls, ID requires knowing the species of oak. It is also critical to look at the internal structure:  Even then, there are some very similar ones, and it may be necessary to examine the adult wasp that emerges.”  A British Website has a photo that matches your Gall, and it is identified as Biorhiza pallida, but we believe your new world species is not the same. According to BugGuide there are  “Over 750 species in North America in 49 genera” and “Small to minute, usually black, with characteristic shape: the abdomen is oval and somewhat compressed and shiny, the second tergum covers a good part of the abdomen. Each species makes a characteristic gall on a specific part of the plant. Many make galls on oaks. Most have a complex life cycle with a parthenogenetic generation and a sexual one. Each generation makes galls of a different appearance and on different parts of the plant. The recognized expert in this family is Charles Kinsey who died about 50 years ago after achieving worldwide fame for his studies of male and female sexuality.

Letter 5 – Galls on White Oak

 

White Oak Gall (you don’t have a picture of.)
Location: Murrysville, East of Pittsburgh, PA
October 28, 2010 4:18 pm
Hello Bugman,
I took pictures of some galls on my white oak tree today (10-27-10) I couldn’t find any pictures of these either on BugGuide or on this site. They are ONLY on my white oak tree – not on any other oak tree in my yard. (Pin oaks, shingle oaks) And there are hundreds of these galls. I find it interesting that they have turned pink as the leaves have turned red, since they are made of leaf tissue. They flick off the leaf easily and are wet when squished. This tree is about 15 years old and I do not recall ever seeing these galls on it, although I have seen other types. Thought you might like these pictures for your files.
Signature: MPK

Galls on White Oak

Dear MPK,
There does seem to be an infinite variety of Galls that can be found on oak trees, and we wish Alfred Kinsey were still alive and working to classify the Gall Wasps that produce these harmless growths.

Galls on White Oak

Letter 6 – Galls on White Oak

 

White Oak gall
Location: Great Smoky Mountains National Park, TN
December 16, 2010 10:57 am
I’ve been seeing this gal on white oaks the past couple years in and around Great Smoky Mountains National Park TN. I looked at the picture on your site and didn’t see any that seemed to match. Wold love to have an idea of what kind this is and assume it is a wasp gall?
Signature: Ken Voorhis

Galls on White Oak

Hi Ken,
Thanks for sending your photos.  Galls are growths that can be attributed to many different kinds of insects including wasps and flies as well as to certain mites and other causes that are not related to arthropods.  In the case of Gall Wasps in the family Cynipidae, the Gall is a growth on the plant, often the leaf, that provides food for the larval wasp and does not harm the tree.  Oak trees are probably the most common host to Galls.  There is much diversity in Gall Wasps and we do not have the necessary expertise to classify your particular galls, but you can view some of the genera posted to BugGuide.  There is also a section of unidentified Galls available on BugGuide.  Alfred Kinsey, who gained notoriety in the 1950s with his studies on human sexuality, was an entomologist who specialized in Gall Wasps prior to turning his attention to the private lives of humans.

Galls on White Oak

Thanks Daniel, If I find anything more I’ll forward it to you.
Ken
Ken Voorhis            Executive Director
GREAT SMOKY MOUNTAINS INSTITUTE AT TREMONT
Great Smoky Mountains National Park

Letter 7 – Galls on Oak Leaf

 

Subject: Strange eggs on dead leaves
Location: Kansas City, MO
December 1, 2012 6:25 pm
Been seeing these little egg sac things on dead leaves all over. I am in Kansas City, MO. Any idea?
Signature: Celina

Oak Leaf Galls

Dear Celina,
These are not eggs.  They are Galls and they are produced by a tiny Gall Wasp.  They are produced as a larva feeds, and eventually an adult Gall Wasp will emerge from the gall.  The Galls in your photo are somewhat unusual in that they are on the top surface of the oak leaf.  We tend to see more Galls form on the underside of the leaves.  We will try to determine a little more specifically the identity of your Oak Leaf Galls.  We do not want to totally discount that these Galls might be produced by some other creature, like a mite or a fly.  See BugGuide for more information on Gall Wasps.

Oak Leaf Gall

Letter 8 – Eastern Oak Bullet Gall

 

Subject: What sort of gall is this?
Location: Northeast Tennessee
March 28, 2014 7:47 pm
I found this gall on what I believe to be a small oak tree in my backyard. I’m not very familiar with the various types of galls, but I know that they can be caused by wasp larvae or fungi. I’m curious to know the origin of this one.
Signature: Erin

Eastern Oak Bullet Gall
Eastern Oak Bullet Gall

Dear Erin,
We believe this is an Eastern Oak Bullet Gall, which we found pictured on the Henderson State University Plant Gall Page.  It is described as:  “smooth, spherical galls approximately 1/2 inch in diameter produced by a wasp of the genus
Disholcaspis. These galls are very hard because they form from the tough, woody tissues of twigs.”  According to BugGuide, the species Disholcaspis quercusglobulus:  “Forms round, detachable twig galls, 8-15 mm in diameter, singly or in small clusters, on white oak (Quercus alba).”

Letter 9 – Oak Apple Gall

 

Subject:  Unknown Moth Chrysalis?
Geographic location of the bug:  Northern VA
Date: 05/18/2019
Time: 03:06 PM EDT
Your letter to the bugman:  Hello, I was walking today (May 18) and found this unusual growth on a small tree sapling off of the neighborhood trail. I’ve searched but have only found one image even close and it was a silk moth chrysalis.
How you want your letter signed:  N. Celata

Oak Apple Gall

Dear N. Celata,
Your sapling appears to be a young Oak and this is a Gall, a growth that appears on plants and is often caused by an insect.  Oaks are hosts to many different Gall Wasps that produce Galls.  Based on images posted to Discover Life, we believe this is an Oak Apple Gall,
Amphibolips confluenta.

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.

4 thoughts on “Oak Gall: All You Need to Know for Amazing Remedies and Crafts”

  1. I have found a pure white twig gall that came off of my red oak tree. It is a perfect 1/2″ dia and hard as a marble. It is white as snow. Anybody know what this is? I have seen pics of several gall but none this color or size and shape. HELP PLEASE!

    Thank You,
    Old LB

    Reply
  2. I have found a pure white twig gall that came off of my red oak tree. It is a perfect 1/2″ dia and hard as a marble. It is white as snow. Anybody know what this is? I have seen pics of several gall but none this color or size and shape. HELP PLEASE!

    Thank You,
    Old LB

    Reply

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