anonsally: What are the potato-looking things on the scraggly…

Tuesday, February 25th, 2020


What are the potato-looking things on the scraggly tree? @lies?

They look like galls. If you zoom in at least one has little round holes that look like emergence holes. Cynipid wasps make galls like this in oaks; do you know if that’s an oak tree? Identifying what insect (usually) or fungus (sometimes) induced a gall usually starts with identifying the plant involved, since most gall inducers specialize in one or a few related species of host plant.

Ron Russo’s Field Guide to Plant Galls of California and Other Western States is wonderful, as is Noah Charney and Charley Eiseman’s Tracks and Signs of Insects and Other Invertebrates. I highly recommend both!

Thanks for sharing this!

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I’ve spent a fair amount of time paying attention to Baccharis…

Thursday, July 11th, 2019

I’ve spent a fair amount of time paying attention to Baccharis pilularis galls, and don’t recall ever seeing any that looked like this.

Hey @crudlynaturephotos, do you have any idea what made the galls? If not, would you be cool with posting the photos (or letting me post the photos) to I bet Charley Eiseman would have a good idea what made them.

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I assume you are probably already familiar with it, but if not I highly recommend Charley Eiseman and Noah Charney’s book Tracks & Signs of Insects and Other Invertebrates. It’s a fantastic guide with lots of detail about things like galls and egg cases and silken hides and whatnot. Great photos and explanatory text. Charley’s also awesome about responding quickly to mystery photos posted to Bugguide. Thanks for posting so much cool content! I’m glad I found your blogs. :-)

Tuesday, March 28th, 2017

Hello there! Funny you mention it, I discovered Charley Eiseman yesterday while I was trying to ID some tricky galls I found in my yard last week. I only noticed them after I crouched down to investigate the harlequin bug eggs that were attached to a nearby sapling [link]. The pink caught my eye, and since I was in “excited insect egg” mode, I thought these were eggs of some sort. I’m new to trying to ID eggs, so that was my wild guess since I hadn’t seen any galls like this in person. Technically, they’re not not eggs?


I posted them to iNat [link], and didn’t get any IDs from people. The next day, I wanted to go back and check on the harlequin bug eggs, and I noticed MORE pink spikes on another leaf, and made another iNat observation [link]:


I am lucky to live in an area with a very active naturalist community. I was at a bioblitz on Sunday and met a guy I have been interacting with pretty heavily on iNat (I love introducing myself to people with my username and see how excited they get to meet me in person!). This guy saw my observation of these galls and identified the plant as a hackberry. Knowing the host plant is the most important step in doing these gall IDs, and after I googled “hackberry gall,” I saw a picture of my galls after scrolling for what seemed like forever:


Image is © Charley Eiseman, see his post about them here [link]. The image above is of the Hackberry Horn Gall (Celticecis cornuata) specimen he sent off to the entomologist who described this midge as a new species in 2013. 

You cannot comprehend how excited I was to (1) ID this under-documented species (there is currently only one, not so great photo of these galls on bugguide [link]–I submitted my photos as an ID request because I kept getting yelled at for being wrong, but nobody’s commented on my page [link] so I might just add my photos anyway) (2) be one of the few people to see AND document it, and (3) specifically request an iNaturalist admin to add the species page because it wasn’t in the system yet.

Next steps: I’m going to go back out into my yard at some point this week and see if I can dig up the sapling these are on and move it closer to the house. I want to watch them hatch! Also, I have access to some pretty fancy microscopes at work, so I can dissect one under a light microscope, and THEN use the scanning electron microscope to get super high resolution images. STAY TUNED.

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dendroica:Eastern False Willow, a.k.a. Groundsel Bush (by…

Monday, October 17th, 2016


Eastern False Willow, a.k.a. Groundsel Bush (by me)

Fun fact: This species (Baccharis halimifolia) has become an invasive weed in Queensland, leading authorities there to import my favorite gall midge, Rhopalomyia californica, as a biological control. R. californica normally galls my plant-crush Baccharis pilularis, but in the absence of B. pilularis they’ll make do with B. halimifolia, thereby replacing flower production with midge production and slowing the spread of the unwelcome plant.

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more identifying animals from plants

Friday, September 23rd, 2016


 photo IMGP3623_zpsflg8ywqh.jpg
Every growth, marking, bump, or blemish on a plant was made by something, and surprisingly often the cause can be closely traced to a particular animal. I could see from a distance that these hickory leaves had orangish spots on their underside.

 photo IMGP3622_zpsspjkkcig.jpg
On close examination the spots were furry balls! These little growths are galls that have grown around insect eggs, in a weird bit of mostly harmless and stunningly common parasitization.

 photo IMGP3618_zpsjcssqize.jpg
These orange tribbles hide and protect the larvae of the hickory gall midge (Caryomyia sp.). The creature inside is a helpless pinpoint of a maggot that will grow into a fly so small that it would otherwise go completely unnoticed by humans.

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freespiritandmindaz: Nature is so beautiful… look at this…

Sunday, September 4th, 2016


Nature is so beautiful… look at this beautiful display of the prickly rose gall. These galls are a parasitic sack formed by the cynipid wasp. The wasp, like many other parasitic insects, uses the wild rose plant as a safe haven for its offspring. They inject a substance into the plant and then lay their eggs in it, as the larva grows, so does the gall and that is what the larva uses as a food supply and as a protection sack until they are ready to join the world. You would think this type of parasitic infestation would be damaging to the host plants, but research shows that the plants are not affected by these types of infestations.

I find galls very interesting and these ones in particular are one of my favorite… the wasp that created these galls was surely an artist… it used the leaves to create the perfect bed for its children <3 here is another perfection of Nature’s artistry…

#galls #insects #parasitic #parasiticwasp #cynipidwasp #natureswonders #naturesbeauty #freespiritandmind #art #artistry #plantgeek #plantlove (at Love Nature)

Diplolepis polita is the wasp’s scientific name. These galls show up in the California wild rose (Rosa californica) at the Carpinteria salt marsh; I love showing them off to tour attendees. Russo discusses the species extensively in Field Guide to Plant Galls of California and Other Western States.

I’ve always wondered if the spines (which are flexible at first, then become brittle with age) represent the wasp repurposing the genetic code that produces the rose’s thorns.

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waitingfortheweek: Interesting gall on a Canadian…

Friday, August 12th, 2016


Interesting gall on a Canadian thistle

This reminds me of the galls produced in Coyote Brush (Baccharis pilularis) by a small moth, Gnorimoschema baccharisella. Some googling suggests yours might actually be Urophora cardui, however, a type of gall-inducing fruit fly that has been imported from Europe in an effort to control the invasive thistle.

Thanks for sharing the image! The Tumblr gall fandom: small but doughty.

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flowersofantimony: Bundling goldenrod galls to…

Tuesday, April 19th, 2016


Bundling goldenrod galls to put in our nature elements section of the shop

#organic #floral #arrangement #nature #inspiredbynature #galls #goldenrod #plantlove #forestdweller #foraging

my kind of bouquet

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Carpinteria Bluffs, 2016-02-20It was overcast at the bluffs…

Sunday, March 20th, 2016

Carpinteria Bluffs, 2016-02-20

It was overcast at the bluffs today, but the clover (Oxalis sp.) and black mustard (Brassica nigra) were in bloom and doing their best to brighten the scene. They’re non-native, and so are frowned-upon from a restoration-ecology perspective, but so far that patch of ground has been left to its own devices. In a coastal SoCal field a month or so after a rain that usually means clover and mustard. Anyway, I thought it was pretty.

One of the benefits of restoring native plants is that they tend to host a nice assortment of insect associates. There was evidence of that in the nearby coyote brush (Baccharis piluarlis), where a new outbreak of green leaf beetles (Trirhabda flavolimbata) is under way. It’s early on in the outbreak, so I didn’t see any adult beetles, but the larvae are definitely getting bigger then they were a few weeks ago, when I first noticed them coming back.

If this outbreak follows the pattern of the last few I’ve seen there eventually will be multiple generations of beetles from tiny larvae to shiny green adults crawling all over the plants, many of which will end up completely defoliated. The coyote brush doesn’t seem to mind too much; a year after the last outbreak they were back in business.

The last photo above is of a small coast live oak (Quercus agrifolia) that was heavily galled with stem galls. I’m thinking those are probably the work of the cynipid wasp Callirhytis quercussuttoni. According to Russo’s Plant Galls of California and Other Western States (which I love), the generation of wasps that emerged through those exit holes you can see were all females; they lay their eggs on leaf buds, which produces a generation of small leaf blister galls that host both males and females. After mating, the adult females of that generation oviposit into young, growing stems, which eventually results in the big stem galls you see here.

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thingsondesk: i love galls.  galls galls galls.  When i see…

Friday, July 17th, 2015


i love galls.  galls galls galls.  When i see organisms other than humans create structures, it blows my mind!  like a form of pure function.  soooooo awesome!

Allie, who’s working on imaging flies, which I’ll show you guys in future times, was showing me galls last week because she knows how much i loves em.  galls and nests.

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ladyjeanetteavenel: Oak galls, used for making Ink. I wonder…

Tuesday, April 14th, 2015


Oak galls, used for making Ink. I wonder why a tree would make them?

Apologies if I’m explaining something you already know.

I’m not a gall expert, but from the little I know I suspect these galls were made in response to a wasp in the family Cynipidae laying its eggs on the stem. The oak then responded to the presence of the eggs (or maybe to the larvae that hatched from them) by producing the galls, which are masses of abnormal plant cells not unlike a benign tumor in an animal. The wasp larvae live and grow inside the galls, feeding on the plant tissue.

The actual mechanism whereby gall inducers interact with the host plant to create galls isn’t well understood. Gall researchers speculate that it involves some combination of chemical, physical, and/or viral triggers.

I kind of have a thing for galls, if that wasn’t obvious.

More reading:

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Insects associating with coyote brush (Baccharis pilularis) at…

Monday, February 9th, 2015

Insects associating with coyote brush (Baccharis pilularis) at the Carpinteria Salt Marsh, February 8, 2015.

My search for a Rhopalomyia californica emergence event continues. I’ve read that the adults, which only live a few hours, tend to emerge in the morning after a rain. It rained last Saturday, so on Sunday morning I went to the marsh hoping to catch them in the act. These photos show some of the bug-related things I found. (A companion post has non-bug-related pictures.)

I found a lot of galls, more than I’ve seen at any time since last year’s drought knocked their numbers down.

First row:

I didn’t find any R. californica galls with adults in the process of emerging, but I did find some with evidence of recent emergence. The first three photos above show what that looks like. First is a shot of my hand holding a gall to give a sense of scale. (Hopefully I’m not helping biometric-identity thieves by posting a photo of my fingerprints.) Next is a closeup of the same gall showing the leftover exuvia of several emerged adults, and finally an even closer shot of exuvia from a different gall.

I’m not sure how long the exuvia (which are the spent pupal case) remain on the surface of the gall, but I’m guessing it’s at least a few months. If I did a better job of monitoring individual galls over time, rather than just wandering through the marsh observing them on a particular day, I probably could answer that question.

Second row:

Most of the R. californica galls in the marsh are green or yellowish-green, but a few of them are magenta. I have no idea why that is. I’m not aware of any non-gall-related structures on coyote brush with that color. The biochemical/genetic interactions between gall-inducing species and their host plants are quite mysterious, especially to a layperson like me. I wonder if the magenta galls have different properties aside from color. Are they thicker-walled? Do they represent a genetic variation in the gall inducer, or are they just a more-or-less random result of the particular site on the plant where the adult midge lays its eggs?

The righthand image shows the gall of a different Rhopalomyia species, R. baccharis. This is what Russo (who first described the species) calls the “twisted stem gall”. The adult insect is indistinguishable from R. californica except by genetic analysis, but the gall is completely different. Instead of a fleshy round gall containing several larvae at the tip of a stem, R. baccharis creates a thickening of the plant stem that has a characteristic series of S-curves, with one larval chamber below each bend. This isn’t a very good shot of the gall itself, but it shows the gall’s characteristic elliptical emergence hole. That hole isn’t created directly by the larva; instead, there is some sort of communication that takes place between larva and plant that triggers the plant to create that opening at the time the larva pupates, clearing the way for emergence.

I wonder if there are advantages to developing inside the coyote brush’s stem rather than in a bud gall. The outer covering of stem galls is tougher, which I’m guessing helps protect the larvae from the ovipositors of parasitoid wasps. But that also means the larvae’s jaws probably aren’t adequate for chewing their way out, the way R. californica larvae do. It’s mind-boggling to think about the shared coevolutionary history between plant, gall inducer, and predators/parasitoids that led to the current situation.

Third row:

Here’s a photo of another one of my favorite coyote brush galls, that of the moth Gnorimoschema baccharisella. I didn’t notice it while taking the photo, but I think those may be two more G. baccharisella galls growing at the tips of the stems to the left and right of the large gall, with a fourth one visible in the photo’s lower righthand corner. My guess is that those are all from a single egg-laying session; unlike Rhopalomyia galls, G. baccharisella galls are monothalamous, meaning there is only one larva per gall.

The middle photo shows some kind of hide constructed from a number of leaves stuck together. I don’t have any idea what made it, and didn’t want to tear it apart to try to find out. I’m going to post my photos of it to Bugguide and see what Charley Eiseman thinks.

Finally, the Trirhabda flavolimbata leaf beetles are coming back, with a number of bushes showing signs of being munched by beetle larvae. Most of the larvae are still quite small; only a few millimeters long. This is one of the largest ones I found; it was about a centimeter. I wonder if this will progress to a full-on outbreak like it did last year, or if instead the beetle numbers will stay low, allowing the plants to escape widespread defoliation.

Previous ravings about the galls I talked about here are in these earlier posts: Baccharis pilularis galls at Solstice Canyon, Malibu (including bonus I Didn’t Write This content), and Bugs at the marsh.

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Public Service Announcement

Saturday, March 8th, 2014

It is a sad fact of the Tubmlr tagging system that the number of people who think “gal” is spelled “gall” is roughly equal to the number of people actually interested in galls.


These are gals:


…while these are galls:






Thank you.

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Baccharis pilularis galls at Solstice Canyon, Malibu I mentioned…

Tuesday, February 11th, 2014

Baccharis pilularis galls at Solstice Canyon, Malibu

I mentioned before that one of the things I enjoyed about Yulin’s beautiful I Didn’t Write This Ep. 2 (the one with Auden’s “As I Walked Out One Evening”) was the setting. They shot the video in Malibu’s Solstice Canyon, which I’d never visited before. It looked like there was some coyote brush (Baccharis pilularis) in some of the shots, but I wasn’t sure, and since yesterday was my once-every-two-weeks mega-commute via Malibu, I decided to check it out on my way to work.

I really loved it. There’s water in the stream year-round, and the riparian habitat along the main trail was super birdyish. I didn’t have my binoculars with me (which was just as well, or I probably would have been late to work), but the southern California nesting season is getting under way, so there was lots of singing. Yellow-rumped warblers, oak titmouses, California towhees, spotted towhees, and white-crowned sparrows were everywhere.

The upper slopes (which I didn’t have time to hike to) looked too xeric for coyote brush, but down near the creek there was a fair amount of it. It was more spindly than the plants I’m used to near Santa Barbara, and the seed heads on the female plants seemed a little less profuse; I suspect that’s because Malibu is warmer and dryer than where I live. There also was less coyote brush overall in the habitat; individual plants were scattered around, rather than occurring in extensive stands.

When I’m around coyote brush I always look for galls. There were relatively few Rhopalomyia californica galls compared to what I’m used to, but I found some that you can see in the middle row of photos above.

You’ll probably think I’m an idiot to feel this way, but I get choked up when I think about the midges that induce those galls. They spend most of their lives as tiny maggots inside the gall, feeding on plant tissue. Then they chew their way to the surface and pupate, their body liquifying before transforming into an adult midge, and then finally, on a particular cool morning, often a day or so after a rain, a bunch of them emerge together.

The females’ abdomens are already orange and swollen with eggs. The males mate with them and die; the females lay their eggs before dying a few hours later.

They live their whole lives for that one day. I’ve never seen a Rhopalomyia emergence in-progress, though I keep looking. Once I found a dead female a day or two after emergence, a sticky trail of eggs connecting her to the plant, dead in the very act of laying her eggs. Will my own life have a dramatic climax like that? Probably not. I’ll just get older and crankier, and eventually something will take me out. But that Rhopalomyia midge died a heroine, fulfilling the point of her existence in her final moments.

Besides the R. californica bud galls, I also found a couple of stem galls made by a moth, Gnomorischema baccharisella. You can see them in the bottom row of photos. A cool thing about these galls is how different the ecology of the gall itself is, compared with the similarly sized R. californica galls that grow on the same plant. The Rhopalomyia bud galls contain multiple larvae, but a G. baccharisella stem gall contains only a single caterpillar. The larvae in the bud galls don’t produce frass (insect poop). I’m not sure what happens to their waste; either they don’t emit any, or it somehow is excreted and carried away by the plant. That latter explanation seems kind of unlikely, but I don’t actually know much about insect/gall interactions, and over evolutionary time scales gall inducers and their host plants have evolved pretty complex relationships.

The caterpillar in the stem gall does produce frass, which accumulates inside the gall. When the caterpillar gets old enough it chews its way out and drops to the ground to complete its development. But now there is a convenient hole in the gall (you can see it in each of the galls pictured above, meaning both of those galls have already lost their original caterpillar), and a bunch of other organisms move in. Colonies of fungi grow on the frass, and fungus mites that eat the fungi, and other creatures that prey on or parasitize the mites. There are whole little worlds in there, and that’s just one type of gall on one type of plant.

When I give in to the temptation to talk about plant galls during docent tours at the marsh, someone usually asks about the nature of the relationship. Are the gall inducers harming the plant? Helping it? And what they’re really asking is, are these good bugs or bad bugs?

It’s a good question. Looking strictly from the perspective of the plant, the gall inducers are harmful. In parts of Australia, where groundsel bush (a close relative of coyote brush) is an invasive weed, R. californica has been imported as a biological control, because the bud galls take the place of flowers, reducing the plant’s reproductive success. In effect, R. californica harnesses the plant’s activity and channels it into producing more R. californica midges, rather than producing more coyote brush.

But the plant’s perspective isn’t the only one. From the point of view of the larger ecosystem, gall inducers are just doing what nearly every other organism has done before it: Finding a niche in the pre-existing biome within which it can survive, adding one more layer to the mind-bogglingly rich assembly of interrelated living things that make up all life.

From that perspective, what gall inducers do is awesome and cool. Certainly the fungus mites that specialize in living inside old G. baccharisella galls would say so, if you could ask them, as would the dozen or more species of parasitic wasps that prey on R. californica, or the hyperparasites that prey on those parasites, or the specialized bacteria that live in the guts of those hyperparasites, and so on, as far as human curiosity can take you. The more I learn about this, the more I believe that people like James Lovelock and the late Lynn Margulis were on the right track in arguing that we spend too much of our time focused on the organism as the most meaningful level of biological organization. We also need to think about life as a whole.

One other thing I liked about Solstice Canyon: Its parking lot was nearly full, but it’s a small lot, and the people who were there were really nice. I think the fact that it’s kind of hidden away on a side road means you’re only going to get people who make a point of seeking it out, and that selects for a certain kind of visitor.

At one point I was standing under a big sycamore, trying to see a woodpecker that I could hear drumming. Two people, an older woman and a younger woman who might have been her adult daughter, were standing not far away. I didn’t notice them paying any attention to me, but when I walked past them the younger woman asked me if I’d been looking for the bird.

“What?” I said, not because I hadn’t heard what she said, but because I’m shy, and a dork, and I’d been shocked out of my big-city bubble by a stranger willing to talk to me.

“Were you looking for the bird?”

“Oh, the woodpecker? Yeah. I couldn’t see it, though.”

“I’ll show you,” she said, and walked back a few feet to point out the bird, an acorn woodpecker that was hammering away at the underside of a dead limb.

“Thanks,” I said, and smiled, and she smiled, and we went our separate ways. And maybe it was just me being maudlin from thinking about Yulin’s video, which made me cry when I watched it — because of the music, and the images, and Auden’s words, and Sean’s delivery — but it just seemed like a really nice thing of that woman to do, noticing that I’d been looking for the bird, and helping me see it.

tl;dr: I had a really nice time at Solstice Canyon, and I’m happy I followed Yulin’s recommendation to visit it.

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Bugs at the marsh Here are more photos I’ve taken recently…

Friday, August 9th, 2013

Bugs at the marsh

Here are more photos I’ve taken recently at the Carpinteria salt marsh. These all relate to arthropods (to insects, mostly, plus one spider), so I’ve put them in a separate post to help anonsally avoid them with Tumblr Savior.

The outbreak of green leaf beetles (Trirhabda flavolimbata) that defoliated much of the marsh’s coyote brush (Baccharis pilularis) has now ended. There are only a few adult beetles left, and the coyote brush has started putting out new leaves. I took the photo above on July 14, when the beetles were still fairly easy to find.

The next image is of a syrphid fly in the genus Allograpta; probably A. obliqua or A. exotica. I took this photo the same day as the beetle photo and just a few feet away; both insects were sitting motionless at the tips of their respective stems, giving me time to take lots of shots until I got the focus right. Syrphids (also called hover flies or flower flies) act like bees, hovering to drink nectar from flowers and serving as important pollinators. They don’t have stingers, but have evolved warning colors like bees and wasps to confuse predators into leaving them alone. This is “Batesian mimicry,” named after 19th-century British naturalist Henry Walter Bates, who first observed it in South American butterflies. Whenever I hear the term, though, I think of Mrs. and Miss Bates from Emma.

Next are a couple of photos of super-cool twisted stem galls in coyote brush. The galls are the work of Rhopalomyia baccharis, a tiny midge. The adult midges look identical to their close relatives, Rhopalomyia californica, which I’ve blogged about before, but the galls are completely different. R. californica galls are the size and shape of a marble, and are found at the end of coyote brush stems. R. baccharis galls take the form of these thickened S-curves in the stem itself. A single larva lives in a chamber below each of the gall’s curves. Unlike R. californica larvae, which chew their way to the gall’s surface before they pupate, R. baccharis larvae pupate deep within the gall. Then, somehow, they trigger the host plant to create a tunnel leading to an elliptical exit hole just in time for the adult midge to emerge. The lefthand image above shows me holding a gall to give a sense of scale, while the righthand image shows a different gall with one of those elliptical exit holes.

There is a patch of coyote brush near the marsh amphitheater that has a bunch of these galls right now, and I’m really excited about it, because although I’ve looked for them for years I’ve previously only found a few of them. Hopefully the city Parks and Rec. Department gardeners won’t prune these, as they previously did for another batch of twisted stem galls I found at the marsh.

The next image shows me holding another kind of coyote brush gall. This is the work of a moth called Gnorimoschema baccharisella. A single caterpillar lives inside the gall. When it’s ready to pupate the caterpillar chews its way out and burrows into the ground. But that’s not the end for the gall. Now that it has that convenient hole, a bunch of other species invade it. Fungus grows on the departed caterpillar’s frass (droppings) inside the gall, fungus mites arrive to feed on the fungus, and probably lots of other things happen that I haven’t learned about yet. You can read more about G. baccharisella and see some video I took of a fungus mite running around inside an old gall at my Carp Without Cars blog.

The last image above is not of a gall, but of the kind of thing many observers mistakenly think galls are: an egg case. Specifically, an egg case of the bolas spider (Mastophora cornigera). Bolas spiders have an amazing hunting behavior: They catch their prey not by weaving a web, but by letting out a silken thread with a sticky blob on the end, then waving it around to lasso passing moths. To help improve their chances, the blob gives off a chemical scent that closely imitates the pheromones of the target moth species. Researchers have found that the bolas spider varies the chemical signature of the scent lure over the course of the night, to better match the pheromones of different moths species that tend to be active at different times.

I wrote more about the bolas spider in another post at Carp Without Cars, so check that out if you want. You can also watch a really cool video from David Attenborough’s Life in the Undergrowth series, showing a bolas spider capturing its prey. It’s kind of creepy to watch, even for someone like me who has worked for decades to overcome his arachnophobia, but I think it’s worth it.

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scientificillustration: Galls and Gall wasps (Cynipidae) From:…

Thursday, August 1st, 2013


Galls and Gall wasps (Cynipidae)

From: Les Cynipides. Traduit et annoté par J. Lichtenstein, suivi de la classification des Cynipides d’après G. Mayr. 1re ptie., Introduction. La génération alternante chez les Cynipides.

The gall fandom is small, but we’ve been around longer than you think.

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Leaf Bumps

Tuesday, June 18th, 2013


Did you know that the bumps under a leaf especially red ones are wasp eggs? Other insects too. So, for every single one you see, KILL IT, unless you like wasps and their stings.


They’re not eggs. Well, they could be eggs, since I don’t know exactly what you’re describing. But insect eggs are tiny. What you’re talking about are probably galls.

Galls aren’t eggs. They’re swellings that a plant creates in response to a gall-inducing organism (often a wasp, though other types of insects and some non-insect species cause galls as well). The gall inducer’s larvae then live inside the gall, feeding on the plant tissue.

Galls are fascinating, and sometimes beautiful. Gall-inducing wasps tend to be tiny; a quarter-inch to a half-inch long. They can’t sting you. By destroying a gall you aren’t protecting yourself. You’re just killing another living thing for no reason.

Here are some galls that look like what you might be describing. These were on the underside of the leaves of an arroyo willow (Salix lasiolepis) at the salt marsh near where I live. I believe these were probably caused by a sawfly from the genus Pontania (not actually a wasp, but the adults look sort of wasplike):

My favorite gall inducers are a tiny midge called Rhopalomyia californica. They live almost their entire lives inside a gall they create in coyote brush (Baccharis pilularis), a common shrub that grows along the coast near here.

Adult R. californica midges leave their galls in coordinated emergence events. We don’t know how they time it so they all emerge at once, but it seems to be related to rainfall. What we do know is that about 24 to 48 hours after a rain, adult midges emerge from their galls around sunrise. The adult midges look kind of like small mosquitoes, though they can’t bite. They don’t have mouths. The females are already full of eggs; you can recognize them by their swollen orange abdomens.

Within an hour of emerging, their wings have hardened and they begin looking for a mate. After mating, the males die. The lifespan of an adult male is about two hours.

Females begin laying their eggs on the growing tips of nearby coyote brush stems. They lay as long as they can. The lifespan of an adult female is about eight hours.

It’s easy to find R. californica galls once you know what to look for. Here’s a picture I took of one. You can see the leftover exoskeletons (called exuviae) of the emerged adults:

Finding an adult midge is harder. I’ve never seen an emergence event in-progress, though I keep looking. The closest I’ve come is finding a the body of a dead female a day or two after emergence:

She was still laying eggs when she died. The tip of her abdomen was stuck to the plant, an orange line of eggs trailing from it.

I get that bugs can be scary. A few of them can bite or sting, especially if you bother them. But most of them aren’t interested in harming you. They’re just living their lives.

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