Wool Sower Gall: Essential Facts for Curious Minds

Wool sower gall is an unusual plant growth caused by the secretions of the grubs from a tiny gall wasp called Callirhytis seminator. These fascinating plant malformations can be quite a sight with their unique white and red masses on oak trees. In this article, we’ll provide you with all the essential information about wool sower gall and its formation.

Callirhytis seminator wasps are about 1/8 inch long, dark brown, and have noticeably flattened abdomens. The grubs they produce are translucent to white, plump, and legless. As these grubs develop, they release chemicals that trigger the plant tissue to create wool sower gall, which provides both food and shelter for the developing larvae.

It’s important to understand the life cycle and impact of wool sower gall on affected trees. By knowing what to look for, you can better assess the health of your trees and make informed decisions about their care. So, let’s dive deep into the world of wool sower gall and quench your curiosity.

Understanding Wool Sower Gall

Wool sower gall is a unique and unusual plant growth caused by the secretions of the grubs of a tiny gall wasp, called Callirhytis seminator1. The galls are usually white, fluffy, and can be found on oak trees2. In this section, you’ll learn more about wool sower gall, gall wasps, and their intriguing relationship with plants.

The gall wasps are small, with a length of about 1/8 inch, dark brown, and have noticeably flattened abdomens1. The grubs they produce are translucent to white, plump, and legless1. Gall wasps have an interesting life cycle which involves the alternation of generations2. One generation develops in leaf galls, while their offspring develop in another type of gall, called stem galls2.

Wool sower galls aren’t harmful to the host plant. In fact, mature plant tissues are generally unaffected by gall-inducing organisms3. The gall continues to grow as the insect feeds and develops inside it3. Even if the insects die, the galls will keep forming3. Most galls remain on plants for more than one season, as they only become noticeable after they’re fully formed3.

To sum up, wool sower gall is an interesting phenomenon in the world of nature. Caused by the small Callirhytis seminator wasp, it creates unique growths on plants that serve as a home for its offspring. While they may look odd, they generally don’t harm the host plant, making them a fascinating subject to observe and study.

Basics of Gall Wasp

Wool sower gall wasps, specifically known as Callirhytis seminator, are tiny insects that induce unusual plant growths called galls. The gall wasp adults are about 1/8 inch long and often have a distinctly flattened abdomen.

These insects have a unique life cycle which includes males and females. The female wasps lay their eggs on plants, causing the galls to form as a reaction to secretions from the developing grubs. These grubs are plump, legless, and translucent to white in appearance. The gall provides the wasp larvae with both shelter and sustenance as they grow within it.

Here’s a comparison table highlighting some differences between male and female gall wasps:

Aspect Female Gall Wasps Male Gall Wasps
Responsibilty Lay eggs on plants Fertilize female eggs
Role in Gall Formation Directly responsible for causing galls Indirect role, no direct physical involvement in gall formation

Some features of gall wasps include:

  • Small size (approximately 1/8 inch)
  • Causes galls in plants
  • Distinct and unusual plant growth
  • Unique life cycle

With this information, you now have a better understanding of the wool sower gall wasps and the basics of their biology. Remember to approach these fascinating little creatures with a sense of curiosity for the natural world.

The Process of Gall Formation

Wool sower gall formation is quite intriguing. It starts when a tiny gall wasp lays its eggs on a host plant, typically a white oak tree or other oaks.

When the eggs hatch, the larvae secrete chemicals that cause unusual plant growths, known as galls. These galls can vary in type, such as leaf galls, stem galls, and twig galls.

Galls provide the larva with a safe environment to develop. They offer both nourishment and protection against external elements. Some galls are soft and spongy while others are hard and woody.

Here are some general characteristics of galls:

  • Induced by wasp larvae secretion
  • Can appear on leaves, stems, or twigs
  • Provide a home for developing larvae
  • Vary in texture and appearance

As the wasp matures, alternating generations may occur, meaning one generation develops in one type of gall, while the next generation settles in a different type. For instance, the offspring of the leaf gall generation may go on to form stem galls.

To recap, the gall-formation process typically follows these steps:

  1. Gall wasps deposit eggs on the host plant (usually oaks).
  2. Larvae hatch and secrete chemicals.
  3. Plant tissue reacts and forms galls to enclose the larvae.
  4. Larvae mature within the galls and eventually emerge as adult wasps.

Keep in mind that while galls may appear unusual, they are generally harmless to their host plants and can even be fascinating to observe.

Peculiarities of Wool Sower Gall Appearance

Wool sower gall is quite a fascinating growth you might find on oak trees, especially white oaks. Its appearance is unique and intriguing, and understanding its features can be helpful.

You may notice the galls have a fuzzy texture and come in various colors such as red, white, pink, and brown. What makes them truly peculiar are the seed-like structures inside them, which further add to their distinct look. The tiny Callirhytis seminator gall wasp is responsible for creating these galls that are, despite their unusual appearance, harmless to the tree.

Here are the main features to note when spotting a wool sower gall:

  • Fuzzy texture
  • Colors: red, white, pink, brown
  • Seed-like structures inside
  • Found on white oak trees
  • Caused by Callirhytis seminator gall wasp

Keep an eye out for these interesting growths as you explore nature. You now have a better understanding of the peculiarities of wool sower gall appearance. Remember, although they might look odd, they don’t pose a threat to the tree’s health.

Alternation of Generations

In the world of Wooly Sower Gall, there’s a fascinating phenomenon known as alternation of generations. This process involves two distinct types of galls produced by the Wool Sower Gall Wasp.

The first type of gall is the leaf gall, which houses one generation of wasps. After they develop, these wasps produce offspring that develop in the second type of gall: the stem gall. The interesting part is that scientists are still unsure about the appearance of the alternate generation galls of the Wool Sower Gall Wasp.

As you learn more about Wooly Sower Gall and its unique properties, remember that these alternating generations make it a notable aspect of plant health and insect behavior. So, keep in mind the following features:

  • Wooly Sower Gall involves two types of galls: leaf gall and stem gall
  • The Gall Wasp offspring develop in alternating generations within these galls

Defensive Aspects of Galls

Wool Sower Galls provide a fascinating glimpse into the world of entomology and the protective measures employed by insects. In this section, you will learn about the defensive aspects of these galls.

Galls, like the ones formed by the tiny Callirhytis seminator wasp, serve as protective structures for their developing larvae. These growths offer the following benefits:

  • Protection from predators: The gall’s outer layer acts as a barrier against potential predators such as birds and other insects.
  • Protection from the elements: The gall provides a safe, climate-controlled environment for the developing wasp larvae.

Here’s a comparison table to help you understand the main differences between wool sower galls and other types of galls:

Gall Type Caused By Protection Offered Examples
Wool Sower Callirhytis seminator (wasp) Physical barrier, controlled climate Oak trees
Leaf Gall Various insects and mites Physical barrier Maple trees, eucalyptus
Stem Gall Gall-forming insects like aphids Physical barrier, sometimes nutrients Rose bushes, citrus plants

Keep in mind that galls can have additional benefits for their creators. Some types of galls provide nutrients for the developing larvae, while others may even release chemicals that inhibit the growth of potential competitors.

So, the next time you come across a gall on a tree, take a moment to appreciate the fascinating world of entomology and the remarkable ways insects protect their offspring.

Management and Treatment

When dealing with a wool sower gall infestation, it’s essential to adopt an integrated pest management approach. This will involve a combination of methods to effectively control the pest. Here’s what you should consider:

  • Pruning: Remove and dispose of infested branches as soon as you notice the galls. This helps prevent the spread of the wasp larvae.

  • Chemicals: Use pesticides that target the wool sower wasp specifically. Apply the pesticide when the adult wasp is most active to achieve better results.

Some examples of effective treatment options include:

  • Insecticidal soaps or oils: These can suffocate the adult wasps and larvae if applied directly.

  • Systemic insecticides: These are absorbed by the plant and can kill the larvae feeding on the gall tissue.

However, be cautious when using chemicals to treat wool sower gall. Overuse may harm beneficial insects. Always follow the recommended guidelines for application and dosage.

For the best results, implement a residential Integrated Pest Management strategy:

  1. Monitor your trees regularly for signs of wool sower gall.
  2. If you notice a gall, remove the affected branch immediately.
  3. Use a targeted pesticide as needed, following the guidelines for safe application.

By using this approach, you can manage and control wool sower gall effectively, keeping your trees healthy and pest-free.

Specific Types of Oak Galls

Oak galls come in various forms and are associated with different species of oak trees. Some common types of oak galls include wool sower galls, horned oak galls, and gouty oak galls. Each type has unique characteristics and causes specific symptoms on oak trees.

Wool Sower Galls: Wool sower galls are typically found on white oaks in spring1. They appear as fluffy, cotton-like structures and contain small, seed-like structures where the gall wasp grubs develop2. The grubs are responsible for wool sower galls, as their secretions cause the oak leaves to swell, forming these distinct galls3.

Horned Oak Galls: Horned oak galls form on oak twigs and branches4. They are caused by stimuli produced by certain wasps, leading to abnormal plant growth5. As the galls mature, horn-like extensions protrude from their surface, giving them their name. These galls can impair nutrient and water circulation in the affected branches, which may cause twig and branch dieback.

Gouty Oak Galls: These galls typically form on the twigs and roots of oak trees6. Gouty oak galls are hard, irregularly shaped, and can grow to be quite large, sometimes measuring several inches in diameter. They are caused by another species of gall wasps that lay their eggs in oak buds. When the larvae develop, they release chemicals that stimulate abnormal plant growth, resulting in gouty oak galls7.

Here’s a brief comparison of these three types of oak galls:

Wool Sower Galls Horned Oak Galls Gouty Oak Galls
Affects White Oak Oak Twigs/Branches Oak Twigs/Roots
Formation Time Spring Varies Varies
Appearance Fluffy, cotton-like With horn-like extensions Hard, irregular
Cause Gall wasp grubs Wasps, stimuli Gall wasps, chemicals

In conclusion, wool sower galls, horned oak galls, and gouty oak galls are just a few examples of oak gall types that can affect oak trees. Monitoring and controlling these galls can help maintain the health and vigor of your oak trees.

Associated Risks and Impacts

Wool Sower Gall is caused by a tiny gall wasp, Callirhytis seminator, which induces abnormal growths on plants. These growths, or galls, can look unusual and may impact the appearance of the affected plant. However, it is important to note that the overall health risk to the plant is minimal.

The main issue, when it comes to Wool Sower Gall, is the potential for dieback in affected branches. Dieback occurs when the galls interfere with the flow of nutrients and water in the plant, causing parts of it to wither and die. This can lead to a decline in the aesthetic appeal and overall health of the plant.

Identification of Wool Sower Gall:

  • The galls are distinct, white, and cottony in appearance
  • They can be found on oak trees, particularly the white oak group
  • The galls typically appear in spring, when the wasp lays its eggs on the developing buds

To minimize the risks and impacts of Wool Sower Gall, you may simply prune the affected branches. This will help maintain the overall health and appearance of your plant. While Wool Sower Gall may not cause significant lasting damage, it is essential to be vigilant and proactive in addressing the issue to preserve the beauty of your garden.

Additional Resources

If you’re interested in learning more about Wool Sower Gall, various universities and organizations have conducted extensive research and provide informative resources on this topic.

One prominent institution is NC State University, which offers a detailed publication on Wool Sower Gall wasps, their biology, and the galls they induce. Another valuable source is the N.C. A&T State University, which provides alerts on plant health, including information on wooly sower gall.

Additionally, the N.C. Cooperative Extension County Center features an article on detachable woolly leaf gall wasps, explaining their lifecycle and associations with oak trees. Diving even deeper, the University of Kentucky College of Agriculture provides an informative EntFact publication, discussing various types of plant galls, including the wool sower galls.

Here’s a comparison table to summarize the resources from the mentioned institutions:

Institution Resource Focus
NC State University Wool Sower Gall Wasp Biology and Galls
N.C. A&T State University Plant Health Alerts including Wooly Sower Gall
N.C. Cooperative Extension County Center Detachable Woolly Leaf Gall Wasps
University of Kentucky College of Agriculture Various Types of Plant Galls

Remember to take full advantage of these resources to deepen your understanding of Wool Sower Gall, its causes, and its effects on plant health. Happy learning!


  1. Wool Sower Gall Wasp | NC State Extension Publications 2 3 4

  2. Plant Health Alert – Wooly Sower Gall | Extension Marketing and … 2 3 4

  3. Insect and mite galls | UMN Extension 2 3 4 5

  4. Oak Galls Can Fool Us All | Gardening in the Panhandle

  5. Galls on Oak – Penn State Extension

  6. Gouty Oak Gall – Illinois Natural History Survey

  7. Gouty Oak Gall – Morton Arboretum

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 – Wool Sower Gall


big fuzzy ball
Is this a cocoon? It is growing all over the oak trees in my yard, and the trees are dying. Help! Thanks,

Hi Lynn,
Today we vowed not to do any work that needed to get done until we posted two interesting letters. Your letter officially fulfills our vow. This is a Wool Sower Gall which is produced by a tiny wasp, Callirhytis seminator. Galls are growths on various parts of plants, usually caused by a Gall Wasp or a type of mite. There are many species of Gall Wasps, and each has a specific host plant.The Wool Sower Gall uses the oak as a host. If your trees are dying, it is not because of the Wool Sower Gall as they have no negative impact on the trees.

Letter 2 – Wool Sower Gall


Cocoon on Oak Tree Branch?
Hi — I found your website through Google. I live in central Missouri and found this "weird growth" on a branch of one of the oak trees in my yard. I’ve tried researching the web, but I still can’t identify if it’s a plant fungus, or a gall, or a bird nest, or a cocoon, or something else! Do you have any idea? It’s about the size of a ping-pong ball, white with pink spots, and it’s "perched" on top of the branch. Very strange. Thanks!
Susan Foster

Hi Susan,
In the true sense of the word, this is not a cocoon though adult insects will emerge. You have a Wool Sower Gall which is produced by a tiny wasp, Callirhytis seminator. Galls are growths on various parts of plants, usually caused by a Gall Wasp or a type of mite. There are many species of Gall Wasps, and each has a specific host plant. The Wool Sower Gall used the oak tree as a host. Here is a site with additional information.

Letter 3 – Wool Sower Gall


There is a baseball size cocoon hanging from a maple tree in my yard. It’s white with prickly looking brown things sticking out from it. I really did think it was a baseball for the longest time as I looked at it from my kitchen window. But upon further inspection it’s a cocoon. I’ll take a photo of it and send it along if you’d like me to. After searching the web I can’t figure out what type of cocoon it is. Can you help?
Thanks so much
Julie Worthy

Hi Julie,
You have a Wool Sower Gall which is produced by a tiny wasp, Callirhytis seminator. Galls are growths on various parts of plants, usually caused by a Gall Wasp or a type of mite. There are many species of Gall Wasps, and each has a specific host plant. The Wool Sower Gall used the oak tree, not a maple as a host. Your photo is of an oak tree. Here is a site with additional information.

thanks so much. you can see how much i know about trees from getting the type of tree incorrect. i’m just glad to know millions upon millions of spiders or something like that will not emerge come summer. thanks for your help. i love being able to get information from others on the web who are experts like yourself.
Julie Worthy

Letter 4 – Wool Sower Gall


Backyard Something
This is attached to a lower branch of an oak tree in our backyard! Any ideas to what it may be? We live in Georgia near Atlanta.
Ralph W Sarc

Hi Ralph,
This is the second letter today requesting an ID for the Wool Sower Gall. We were sad the first had no photo and then we opened your letter. The Wool Sower Gall which is produced by a tiny wasp, Callirhytis seminator. Galls are growths on various parts of plants, usually caused by a Gall Wasp or a type of mite. There are many species of Gall Wasps, and each has a specific host plant. The oak tree is the host plant for the Wool Sower Gall.


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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.

  • 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.

1 thought on “Wool Sower Gall: Essential Facts for Curious Minds”

  1. I have found these this spring on shrubbery in my front yard not on trees. Will I harm (myself or the wasp) by removing or cutting these back?


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