Portraits of Wildflowers

Perspectives on Nature Photography

A gooey gall

with 26 comments

Oak Gall with Drops of Goo on It 7435

It’s common to see galls on oak trees, but many of the ones on this live oak (Quercus fusiformis) had sticky drops on their surface that I’d never seen before and still don’t know how to account for. Joe Marcus of the Lady Bird Johnson Wildflower Center provided a couple of good hypotheses: “Apparently it’s an open question.  Does the host tree produce the sticky substance on the gall to capture the exiting adult wasp or perhaps to attract gall wasp parasites, or does the larval wasp cause the gall to produce the exudates to attract others of its species for reproduction?  I don’t think the question has been answered.”

Note the hole in the upper left part of the gall through which a wasp would have exited.

Today’s photograph is from an October 18th field trip to the Shield Ranch southwest of Austin.

© 2015 Steven Schwartzman

Written by Steve Schwartzman

November 7, 2015 at 5:21 AM

26 Responses

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  1. I’m beginning to think that all galls generate at least three hypotheses. So many questions to answer!


    November 7, 2015 at 6:45 AM

  2. According to this source…”These galls also secrete a sticky substance (honeydew) that attracts wasps, bees, and ants. An unusual symbiotic relationship then ensues: these insects feed on the sticky substance and protect the gallmaker from its natural enemies (parasitic wasps).”

    Jim in IA

    November 7, 2015 at 7:32 AM

  3. One of our blog articles contained gall info you might find of interest

    John Bradford

    November 7, 2015 at 10:23 AM

  4. I’ve never seen a sticky gall~very interesting. It does seem plausible that the honeydew would attract insects that would protect the gall provoker. I suspect it is the insect in the gall rather than the tree that is producing it.


    November 7, 2015 at 10:32 AM

    • I don’t recall ever seeing a sticky gall either, so the ones on this tree (yes, there were others) grabbed my attention.

      Steve Schwartzman

      November 7, 2015 at 10:45 AM

  5. Hmm that’s a good one. I wonder if it is the tree. Think Jim is onto something. Great pic btw 😀


    November 7, 2015 at 12:59 PM

  6. Another new experience in a world full of surprises. I’ll join the group who have never seen a gooey sticky gall until now.

    Steve Gingold

    November 7, 2015 at 6:09 PM

    • I hadn’t seen a gooey gall till then either, or even read about the phenomenon. It’s wonderful that there are always new things to learn about and see.

      Steve Schwartzman

      November 7, 2015 at 7:02 PM

  7. I have never seen the sticky droplets before; I am now hoping if I look a little closer I will see this more often, see the droplets, and find an answer as to what causes them.

    Charlie@Seattle Trekker

    November 7, 2015 at 8:44 PM

    • Good luck finding some. I’ve been taking native plant pictures here for 16 years and this was the first time I saw galls with goo on them.

      Steve Schwartzman

      November 7, 2015 at 10:16 PM

  8. Una foto perfecta de la agalla del roble , las gotas la embellecen aún más.

  9. Golly, you have a lot of gall sticking to this subject. (But I’m glad you did, or I’d never have seen such a thing.)


    November 9, 2015 at 11:14 AM

    • They say that seeing is believing, but it’s not necessarily understanding. In this case even the experts don’t seem to know.

      Steve Schwartzman

      November 9, 2015 at 1:46 PM

  10. I see an amazing variety of galls on my walks in bushland here but not seen one with sticky droplets like this. How very interesting!


    November 10, 2015 at 11:16 PM

    • I’m like you in having seen many kinds of galls but never any with drops of goo. Why I hadn’t noticed any in all my previous outings, I don’t know, and you may be asking yourself the same question about your many walks in bushland. Let’s extrapolate and look forward to the many other new things we’ve yet to encounter.

      Steve Schwartzman

      November 11, 2015 at 8:25 AM

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