galls, leaf mines and other tracks and signs of insects (win a field guide!)
READERS REGULARLY EMAIL ME with photos of things they can’t explain, asking for ID’s of balloon-like structures on leaves and twigs; leaves chewed up in a particularly interesting pattern, or with squiggly white lines etched on them. I always go to one book to try to help: the award-winning “Tracks & Sign of Insects and Other Invertebrates: a Guide to North American Species,” whose lead author is Charley Eiseman. Learn about galls, leaf miners and more—and this indispensible field guide.
Charley Eiseman and Noah Charney’s 2010 book is full of photos of all the oddball things you see outside (if you stop long enough to notice!): egg cases and cocoons and all kinds of webs; folded and curled-up leaves as if something’s hidden inside (it is!); and all manner of bumps, lumps, notches, and holes in foliage, bark, you name it. Even tiny previously unexplained pattern in the sand…and soil…a.k.a. tracks and signs of insects.
“I’ve always been interested in everything around me,” says Charley, whose Master’s degree is from the University of Vermont’s field naturalist program. “Then someone gave me a digital camera right after I graduated from college, so I started paying closer attention to the little things. And then I started wishing I had a field guide to tell me what all these signs left by insects and other invertebrates were—but it just didn’t seem to exist.”
Charley and Noah took it upon themselves to create that guide, in “Tracks and Sign of Insects and Other Invertebrates: a Guide to North American Species” (Amazon affiliate link).
“I spent a winter going through every book on insects and spiders looking for anything relevant,” says Charley (who blogs here), “and I was both solving mysteries I’d wondered about for years, as I read the natural histories of all these creatures, and also coming up with additional things to look for.”
my q&a with charley eiseman about galls and leaf mines
Q. People send me photos of green balloons that look like a cherry tomato attached to a leaf, or brown bubbles on oaks, or leaves that look like they are blistering. I know these are examples of galls—but what’s a gall, really? Are they diseases?
A. Galls aren’t diseases. A gall is a deformity in a plant that’s caused by another organism—which could be a fungus or a bacterium or a mite, but many of the most conspicuous ones are insect-caused. There are wasps and flies [including midges] and aphids and a few other insects that cause these galls.
The insect has somehow re-programmed the plant—and in many cases it’s not really understood what is going on physiologically. In some cases it’s just a physical disturbance that’s causing the plant to change its growth, and in some cases it’s chemical, and in some cases I believe it’s actually genetic engineering by the insects.
So the plant is in some way redirected to make this growth that surrounds the developing egg and larva of the insect. And it provides all of the food and shelter that the insect needs as it develops, and then the adult insect emerges when it’s mature.
Q. Now of course everyone who send me these photos is really saying, “What do I do? How do I fix it?” Do we really need to fix it?
A. A gall is really a sophisticated relationship between the plant and the gall-maker, an agreement between the two of them where the insect is just going to damage what might be just one part of one leaf, and the rest of the leaf is free to photosynthesize and go about its business.
Gall-makers are about the least-damaging insect herbivores—they’re not munching the plant down to nothing.
Q. Can galls form on other plant parts, or just leaves?
A. There can be galls on fruits, roots, flowers, leaves—all parts of plants. All are very host-specific and very location-specific, so a particular insect will typically be on one genus if not one species of plant, and on one part of that plant.
Q. So let’s talk leaf mines. Every season my columbine foliage is covered with squiggly white lines, for instance. Is that a leaf mine?
A. A leaf miner is a larva of an insect that lives between the epidermal layers of a leaf. In most cases, they complete their life cycle within a single leaf. If they were removed from the leaf, they generally wouldn’t be able to survive and move to another leaf.
Like the gall-makers, they’re very host-specific.
In columbines, there are two common flies that make the mines: one that makes the linear squiggles you’re describing, and one that makes what’s called a blotch mine, this irregular, blobby shape.
Q. Though we’ve said that for the most part when we see a leaf mine or a gall we needn’t panic, are some destructive?
A. Yes, there are a couple of species that do damage in gardens and farms, such as spinach- and beet-leaf miners, that eat the leaves. A gardener would do well to remove them as soon as they are observed.
But if you don’t see the plant wilting away or the leaves crumpling away, probably nothing to worry about.
Q. I see galls on oak trees, for instance—are oaks particularly popular with these insects?
A. Yes–there are several hundred species of gall wasps that are all associated with oaks alone, and each one has a particular part of a particular oak species that it makes a particular form of gall on. And a lot of them if not all of them have a bi-modal life cycle, where they make one form of gall in the spring, and one in the fall. Ping-pong ball sized ones, other fluffy and white, or dense rosettes of leaves—all different forms of galls. And there are four orders of insects that mine leaves, and all four of them have species that mine oaks.
how to win the ‘tracks and sign of insects’ field guide
I’VE BOUGHT TWO EXTRA COPIES of “Tracks and Sign of Insects” to share with you. All you have to do to enter to win is answer the question in the comments below (NOTE: THE GIVEAWAY IS OVER):
Ever notice a gall or leaf mine in your garden? Tell us more.
Feeling shy, or haven’t seen any but are interested in the field guide anyhow? Just say, “Count me in” or some such reply in the comments box below, and your entry will be counted.
You can buy the books now (Amazon affiliate link) or visit Charley’s website, BugTracks, anytime.
Two winners will be chosen at random after entries close at midnight Monday, September 9, 2013. Good luck to all.
(Photo of round green gall in top collage, and of Charley Eiseman, from Charley’s BugTracks website.)
The top left hand corner picture on your post looks just like something that is on the leaf of my neighbors ash tree. I have been worried if it needed to be treated and could spread. Sounds like this book could be a big help in answering my questions.
Yes! My columbine leaves always have that pattern!
Count me in!
Count me in. Looks fabulous! Thanks, Margaret.
count me in.
Thanks to such wonderful descriptions, I now have gall-envy.
I get gall on the Tilia cordata and there’s this weird one on the Quercus bicolor that looks like an acorn growing in a leaf! Leaf miners in the Aquilegia… always. They almost make the foliage look variegated!
Yes, yes, I need this great guide. My columbines have the squiggly type of leaf miners, and there are galls on the goldenrods in the fields. Also, I’m not sure if those little bumps on some of my river birch leaves are galls? And my pinxter azaleas get some type of large bump that looks like a gall, but it may be some kind of fungus. It starts out chartruse green but turns gray/white over time if I overlook it when I’m cutting them off.
Count me in!!!!
Count me in.
Count me in!
What a great giveaway, I would love to win it! I’ve seen plenty of leaf miners, usually on columbines, but this past spring, for the first time, on my spinach plants. I was so bummed about that, I love spinach, but couldn’t eat any of it. I left them for too long, and they just infested the whole patch.
Often encounter the oak apple gall and the goldenrod gall is “rampant” in the meadow on my property. A guide would sure be handy as it can help decipher between insect “damage” and that of a fungus. Sometimes the two can be quite similar. Thanks!
Baccharis pilularis (coyote bush) has a host- specific midge, Rhopalomyia californica… it produces a really cool shape. I had to do my due diligence to find out that info and would love to learn more! Thanks for the opportunity to try and win this book!
I’ve seen lots of beetle art on old logs, they produce some very interesting designs sometimes. Some remind me of the petroglyphs found on rocks on the coast.
When I was 7 years old, I learned to collect goldenrod galls and use the little worms inside them to fish for small pond & brook trout : -)
I’m also crossing fingers, toes, and eyes for a chance to win this delicious field guide. Also, I need to get out and fish ..
Yes, I see galls all the time! The fuzzy ones are my favorites, like those I photographed here: https://www.itsnotworkitsgardening.com/2010/08/tribbles.html
Fingers crossed for the field guide! :)
I would love to get this book. I used to have a clump of variegated Euonymus that would get galls on the stems and eventually the branch would die.
I have galls on my Oak trees, I broke them apart to show my son the Wasp larva inside. They don’t harm the tree and they are interesting.
We just saw an oak with tons of deep red fuzzy galls. So curious about them. My son would love to head outside with this book.
We live on forty acres in the Ozarks, lots of oaks and oak galls along with all sorts of what is this. Book sounds very interesting.
I’ve got several varigated Euonymous shrubs in my yard, but just one attracts a wasp that produces galls on the wood. The plant is healthy , and not distressed, so I’ve ignored the galls (but they are strange looking.)
I’d love to have the guide for my growing library. Please count me in.
Count me in!!
Yes, galls on bay; leaf miner on a few other plants. Developed, I think, because they didn’t receive enough water.
What a fantastic giveaway! Thank you for the opportunity.
I can’t remember ever seeing galls or miners in my recent gardens, but we must have had miners around when I was a kid. (Beets. So many beets.) Mostly, I see galls when I’m out hiking with the dog. There are loads of oak trees in our forests, and it’s hard NOT to spot at least a few while you’re out and about.