The Gall! Ceanothus As Wasp Habitat

Cynipid wasp on ceanothus leaf00

Cynipid wasp on ceanothus leaf, with gall below.

A young Blue Jeans ceanothus (Holly Leaf Mountain Lilac)  grows along our driveway property line.  Our neighbors practice xeriscaping in their yard, so this border is a drought-tolerant zone.  We want to be good neighbors and do not want to be splashing water through the fence.  So, what better place to install a California drought tolerant native shrub?  Yes!  We will finally plant a ceanothus, or California lilac, a great insectary shrub, full of vibrant flowers, a shrub that wants to be left alone.  Not only is ceanothus low maintenance; it will falter if given any care once established.  Hands off!  Enjoy the buzz of the pollinators and let ceanothus bee, pun intended!

Ceanothus in drought-tolerant zone.

Ceanothus in drought-tolerant zone.   Note the stem/leaf gall infestation created by cynipid wasps.

Two years now and this ceanothus is establishing itself.  But what are those clubbed stalk ends about?  And not just the ends of stalks, but mid stalk, there are a mess, a confusion, a chaos of leaves/stems/lumpy green stuff!  Galls!  This shrub is infested, covered, by galls.  Who is responsible?!  Cynipid wasps, that’s who.  Cynipid wasps are also know as “gall wasps”.  Now I know why.

Ceanothus with clear stems above, cynipid gall below.

Ceanothus with clear stems above, cynipid gall below.   Left stem — newly infected stem begins to curl at tip.  Middle stem — seems unaffected at this point.  Right, below stem — the entire stem end and all its leaves are fused into a gall.

So what is a gall?

Newly formed stem and leaf gall on ceanothus.

Newly formed stem and leaf gall on ceanothus.

Viewing the photo above of the newly formed gall, one can appreciate how a gall is formed.  A gall is the abnormal growth of plant tissue.  In the case of the pictured ceanothus shrub, probably many cynipid wasp adults infected the plant tissue with chemicals.  The chemicals are injected at the end of the stem, in meristem tissue, which is the plant’s most actively growing tissue.  That meristem tissue is very vulnerable; the injected chemical from the insect creates a distortion in the growth process, an abnormality, a beautiful mess of plant tissue.  Note in the photo above, how lush the chaos of stem and leaf is.  Once the inherit rudeness of it all (what nerve! how dare you! what gall!) is passed. the beauty of the created “abnormality” can be savored.  Yes, savored.  Perhaps it’s the ingeniousness of the insect world’s strategy that sways my sense of beauty.

Cynipid wasp larvae inside ceanothus stem gall.

Cynipid wasp newly formed pupas inside ceanothus stem gall.

Galls are larvae motels.  “Mother wasp, you don’t have a place to raise the family?  Then make a  weatherproof  habitat, complete with a food source, for your larvae.”  When the eggs hatch, the worm-like larvae eat their fill of plant tissue, pupate (metamorphosize) inside their cozy sphere, and then eat their way out to young adult freedom, wings and all.

Cynipid wasp pupas in ceanothus gall.

Cynipid wasp pupas in ceanothus gall.  Note the more advanced stage of metamorphosis — the young wasps are starting to take on the metallic green coloring they will have as adults.


Young adult cynipid wasp found in a ceanothus gall.

Young adult cynipid wasp found in a ceanothus gall.   I exposed the wasp while pulling apart the gall (my fingertip on right).

And then the cycle is repeated — more female wasps, maybe even some of those recently hatched, will insert their ovipositors into a fresh stem or leaf to lay eggs.

Old cynipid wasp stem gall on ceanothus.

Old cynipid wasp stem gall on ceanothus.   Each hole represents a hatching cynipid wasp.  This one gall may have housed dozens of wasp larvae.  The stem looks worse for the wear –  further stem growth is halted.   Some of the leaves may continue to live but the shrub must look elsewhere to thrive and grow larger.

So there it is, a stunted shrub on some stalks and perfectly fine growth on other stalks.  And a messy, somewhat unattractive shrub at present, with some nasty and  horrible brown rotten blobs.   This is so challenging my sense of wildlife gardening!

Cynipid wasp in its ceanothus gall habitat.

Cynipid wasp on ceanothus gall.  She is most likely looking for a suitable leaf or gall section to lay eggs, her contribution toward this thriving habitat.

Habitat.  Yes, I want to remember my priority of providing habitat for all of Nature’s creatures in our garden.  Embrace biodiversity includes accepting creatures that inject chemicals into plants JUST to house eggs and provide food and shelter for their young.  JUST!

So there we have it.  Our residential garden is teaming with cynipid wasps.  The wasp are not only pollinators but also food to other animals.  Spiders weave webs throughout the ceanothus hoping to snag one of those wasps.  Birds prey the wasp on the wing.   All is Nature in the wildlife garden.

Enjoy your wildlife garden.  Habitat It!





© 2013, Tony McGuigan. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. If you are reading this at another site, please report that to us

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About Tony McGuigan

Tony McGuigan is the author of Habitat It And They Will Come:  The Why, Who, and Fun-How of Creating Animal Habitats in Your Yard. Tony brings his many diverse skills and passions to Spore Lore’s products and services. His experience as a registered nurse and background in early childhood development, accounting, building, plumbing, sustainable landscaping and gardening—along with being a papa, avid outdoorsman, and enthusiastic student of life—infuses his work as a writer, photographer, editor, and publisher with a uniquely creative perspective, courageous out-of-the box thinking, and immense humor. Related to gardening and ecological landscape design, Tony holds a Sustainable Landscape Professional Certificate from Sonoma State University and a Permaculture Design Certificate from Regenerative Design Institute. Although grounded in cutting-edge research and literature of the field, Tony is pragmatic, not a purist, is unconventional in his landscaping approach yet has an eye for the aesthetic, is a master of reuse and recycling, and is a keen observer of nature and nurturer of relationships—animal, plant and human. Follow Tony on Facebook and also on Twitter 


  1. Sherrie Althouse says:

    Enjoyed your article on the wasp gall but I think the plant in pictured is Baccharis pilularis rather than Ceanothus.

    • Tony McGuigan says:

      Thank you for the comment; I just returned home from vacation. Baccharis pilularis (Coyote Bush)? Could be; I keep an eye out.
      Tony McGuigan recently posted..What Gall! Ceanothus As Wasp Habitat

  2. Donna@Gardens Eye View says:

    Tony I often wondered what a gall was….I will be on the look out in my garden as I am sure many native plants in my garden have the potential to form galls.
    Donna@Gardens Eye View recently posted..Simply The Best Herbs-July

    • Tony McGuigan says:

      Thank you for the comment; I just returned home from vacation. And there are so many types of galls. Some of my favorites are the small red bumps that grow on the underside of fresh green leaves, like willow. Happy gall hunting.
      Tony McGuigan recently posted..What Gall! Ceanothus As Wasp Habitat


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