Galls are everywhere … if you take the time to look … particularly on Oak trees.  The kids and I love insects, so we’ve been actively looking for galls for years. When they learned that one of Barb’s challenges this season included a study on galls, they proclaimed that it was one they were most looking forward to doing.

Galls are caused by many organisms living on plants, including insects, mites, mistletoe, fungi, and bacteria.  We discovered that the Oak is host to more galls (specifically wasps) than any other plant.  This wasn’t surprising as it is on the Oak that we most often observe them.

An “oak apple” gall caused by the California gall wasp (Andricus californicus);
observed on an Oak stem/branch in the spring 2011.

While we were in Norway, we observed the striking red spikes on the leaf pictured below. I had asked around but no one knew what they were.  Months later, I posted my spotting on Project Noah, spotting #7418081.  A recent clue leads me to believe these galls were formed by a mite, Eriophyes tiliae.  These chemically induced galls form an erect, oblique or curved distortion rising up from the upper surface of the leaves of the common lime tree, Tilia x europaea.

Lime Nail Galls
Observed on a leaf in Norway, May 2011.

These mites move onto the foliage in the spring, having overwintered in the crevices of the bark and around the buds.  The mites are less than 0.2 mm long.  The chemicals released while sucking the sap from the lower leaf epidermis creates the colorful, hollow, finger-like extensions to form on the upper surface of the leaf.  Before autumn, the mites, which have been actively feeding and growing inside the galls, depart from their little ‘homes’ and seek shelter elsewhere on the lime tree whereby the cycle begins anew.

Observed on an Oak leaf on the ground in the winter 2012.
Striking “ping-pong” ball galls of the minute gall wasp (Cynips maculipennis)
on the leaves of Oregon oak (Quercus garryana).
Swollen stem galls on the branchlets of a canyon live oak (Quercus chrysolepis)
caused by a cynipid gall wasp (Andricus spectabilis?).
The collection of galls I provided the munchkins as we read about galls.
Buddy’s sketch – sadly, he wasn’t really in the mood and only drew the one.
Sweetie’s sketches … she chose to illustrate several.

As I sat down to write up our lesson, I discovered that alien-like thing pictured below is actually a gall.  I had it in our collection of seeds and cones, however, my online research revealed that it is in fact a gall caused by an aphid-like insect (Adelges cooleyi) of the order Homoptera that invades the needle-bearing branch tips.

Apparently, here in California these are sometimes referred to as Spruce pineapple galls as insects attack the swollen, needle-bearing branchlets of the sitka spruce (P. sitchensis), weeping spruce (P. breweriana) and several cultivated trees, including the oriental spruce (P. orientalis) and Norway spruce (P. excels).  According to W.P. Armstrong, this insect has a complex life cycle that involves two genera of host trees, including several species spruce (Picea) and Douglas fir (Pseudotsuga meziesii).
Insect galls are fascinating. Have you encountered these on your nature outings?



  • Carol ッ

    February 3, 2012 at 3:04 pm

    WOW! You found some really cool galls.

  • Barb-Harmony Art Mom

    February 6, 2012 at 3:13 am

    What a great collection of galls you have! I have seen only a few and my “favorite” is the pinkish red one. We saw those last year and of course we had to bring one home to look at it under the microscope.

    Wonderful gall entry! Thanks for sharing with the carnival.

  • Crafty Cristy

    February 7, 2012 at 1:46 pm

    Thanks for this. We found one of these in the woods several weeks ago, and none of us knew what it was. Very cool to know that there are so many different types of them.We will have to keep our eyes open for them now that we know what to look for.

  • The Glasers

    February 7, 2012 at 1:57 pm

    After reading “Galls are caused by many organisms living on plants, including insects, mites, mistletoe, fungi, and bacteria,” I’m not so sure having a large collection of galls are a good thing! ;-P

  • Barb-Harmony Art Mom

    February 8, 2012 at 10:11 pm

    I thought I had posted a comment on this entry but I don’t see it. This is a great collection of galls and I really enjoyed reading your entry. I have seen the pink one only once in our area…so very interesting.

    Thanks so much for sharing your entry.

  • Pebblekeeper ~ Angie

    February 8, 2012 at 11:21 pm

    Very exciting. I am hoping to find some in our side forest. Now that I’ve seen yours, I’m pretty sure I’ve seen the bottom photo. This might be one search that we keep our eyes out for as we go about town. Thanks!

  • See Jamie blog

    February 28, 2012 at 3:48 pm

    Wow! You found a bunch of galls! Love your kids sketches!

  • Zonnah

    February 29, 2012 at 4:18 pm

    Wow, you really did have a collection of galls. That last one is really stunning.

  • Kristin

    February 29, 2012 at 9:11 pm

    I’ve never heard of a gall, nor have I ever seen one, so this was very interesting!

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