Tunnels from top to bottom

Insect mines under bark surface

When I sat down to enjoy the sunshine and do a bit of sketching in the Don Valley trails on Sunday, I chose a young sapling to sit in front of. Not for any particular characteristic of the tree, but just that I like to have something at my back. I didn’t pay much attention to the tree initially, and I hung my camera bag on a broken-off branch before sitting down. When I got up and reached for my bag, I happened to notice these lines on the bark.

They’re obviously made by some sort of insect. Curious to what it may have been, I started poking around the ‘net. The answer to this question was not nearly as easy to find as I had expected it to be. Between yesterday and then again today I’ve spent several hours typing in search terms into Google and checking out promising links. This is easily the longest I’ve spent on researching a post to this point, and I didn’t even come up with anything conclusive for all that effort.

Insect mines under bark surface

Research for my posts usually starts with a single, rather vague, descriptive term. For instance, when I was researching the Black Knot information, my first term was “black crusty growth on twig”. You usually get a few misses at first before hitting on to what’s obviously the correct identification. In this case I started off with “bark miner”. I’m familiar with leaf miners, which create tunnels between the two surfaces of a leaf, and this looked very similar. It seemed like a pretty obvious connection, but the search produced no viable hits. I changed my approach. “mines under bark lines on surface insect branch”.

This turned up a lot of not very useful stuff, but did contain one page that had something. It was a fact sheet on the Allegheny Serviceberry. What does that have to do with insect mines? It had a section on pests. The first paragraph read, “Cambium miners cause concern when noticed but are not very damaging to the tree. The mines can extend from a twig all the way down to the roots. The mines form light-colored lines in the bark.” Aha! A lead!

So the next search term was “cambium miners”. The cambium is the layer of reproducing cells in a tree located between the outer bark and the inner hardwood which is the source of the tree’s outward growth. It’s just a narrow layer, and in a young thin-barked tree like ash, maple, birch, and other deciduous species, it’s pretty close to the surface. This seemed promising.

Insect mines under bark surface

Most hits I found just simply called them cambium miners, without identifying the species or even the order of insects they belonged to. I didn’t find this especially useful. However, after poking through a number of hits I came across a page from an online resource called Tree Dictionary. The page seemed to be focused on pests of trees as well, and included a lot of information on various fungi. Also paragraphs on sapsuckers, squirrels, frost, beetles, and, the object of my search, cambium miners.

The page indicates that cambium miners are flies belonging to the genus Phytobia. The flies lay their eggs on branches near the top of the tree, and the young larvae mine their way through the cambium down toward the roots, where they stay till they pupate. There isn’t actually a lot of information on the life history of this genus on the web, at least that I turned up in my initial searches. I was able to determine that there are a number of different species that have different host preferences, and some are cambium miners while others are leaf miners.

Insect mines under bark surface

Knowing the species of my tree would help. I’m not certain, as it’s a small sapling in the middle of winter with no leaves. I can rule out birch fairly safely, I would think, and cherry, because there aren’t any horizontal lines. Beech and maple would be grey. Hawthorn would have spines. But that still leaves me with an assortment of options, including common species like ash, and less common ones such as alder, hickory, etc. I’m leaning toward ash, given the location and its commonness.

On the website ForestPests.org I found an informative factsheet on the Ash Cambium Miner. The page indicates that the larvae of this fly mine in straight or serpentine tunnels near the top of the tree, but the further down they get (and presumably, the older they get), the more their tunnels take on a zig-zagging appearance until they’re distinctly so by the time they reach the roots, where they’ll spend about 10 months. They overwinter there, then exit the roots in late spring and pupate in the soil.

I continued to poke around, pressing on and changing the search terms to see if I could turn anything else up. I had a few other potential culprits, including flat-headed borers (metallic wood boring beetles, the group that includes Emerald Ash Borer), and small moths of the genus Cydia, but none of the online resources seemed to match as well. I’m still not positive on calling them Phytobia sp, either, given that I couldn’t find any resource showing their mines to be able to compare to the ones I photographed, but the information all seems to match pretty well.

Laminate floor

Today I spent the day laying laminate floor in the family room at my parents’ house. I’m pretty sure that laminate wood flooring is a little like vinyl tile in that they make the wooden planks out of pressed particleboard (or something resembling it) and then print a design on top, rather than laying an actual wood veneer over it. However, I assume they use an actual image of woodgrain to create the print image, so the laminate planks represent actual woodgrain patterns.

What does this have to do with cambium miners? Well, on both of the sites mentioned above, they indicate that the mines left by the larvae get grown over as the tree continues to grow and result in small discolourations in the wood. These show up as small dark marks on stumps when the tree is cut or, as in the case here, in wooden planking, where they’re called “pith flecks”, among other names. They apparently don’t show up in ash wood very well, but are fairly noticeable in most other types of wood. I’m not sure what type of wood this laminate is supposed to be an imitation of, but it’s got a distinctly reddish tinge.

Pith flecks

Here’s a close-up of the pith flecks in the woodgrain of the laminate print. You can see nearly all of them are associated with the tree-ring growth mark, where the larva would have been tunneling close to the surface of the bark (the dark growth line). A couple of the marks are further in; apparently there are some species that will occasionally feed in the xylem (the layer under the cambium) for short periods, and that could be what these are.

Despite that these marks are due to insect damage, they’re not generally considered defects of the wood by most lumber manufacturers, but they are recognized as such by the Fine Hardwood Veneer Association (who knew there was such a thing?). I suppose that, over the course of a tree’s life, there’s a good chance it will be infested at least once so it would be hard to completely eliminate the marks from wood products.

Insects. They’re everywhere.


Solitude in the heart of the city


This morning I got up early, leaving Blackburnian still asleep in bed, and slipped out the door with my camera and sketchbook to go to one of my favourite spots in the city. Unlike the Rouge, this area is just a short drive, perhaps ten minutes along in-town roads, located in a section of the Don River valley. I discovered it a couple of years ago, when I was hired by the city to do a report for them on one of their properties. This was the area I chose to use as a control site during my study. I chose it initially because it was un-groomed, natural and wild, and over the course of the next several months I really fell in love with the location.

It’s accessed from a small park and playground, through a short, narrow mini-ravine that runs between two rows of houses. The trails are used almost exclusively by the local residents for jogging and dog-walking. I encountered very few people on the trails during my surveys. This morning, in the hour and a half I’m there, I meet no one. This is one of the things I love about the place; it’s quiet, peaceful, relatively undisturbed, and you can almost forget you’re in the heart of the city.


Halfway down the entry trail I notice these snowballs. The sides of the mini-ravine here are steep, and evidently something, perhaps a fallen twig or bit of bark, began sliding down the side of the slope, gathering snow about it as it went. It’s not the typical snowball you see when snow rolls down a hill, and I have to assume that the object slid rather than rolled, and spun as it did so to create these neat doughnut shapes.

Trail with city as backdrop

The entry trail meets up with the main network, and I turn to follow it to the north. It runs along the base of another set of homes. I think how magnificent the view from their back porches must be, and then I think they must command a real premium on house price for such a location. Indeed, most ravine-backing homes are way out of my price range in the city, usually starting at $500-600k for the small run-down places, and going up to well over a million for the really nice ones. Toronto is a wealthy city. It has to be, in order for so many people to live here, with property prices being what they are. In the neighbourhood where we rent you’re lucky to find anything in good shape for less than $300k. I couldn’t afford to buy here on my own. Even Blackburnian and I together would be hard-pressed to find something we could afford jointly. Who are these people, making all this money?

I turn west down a small side trail, and am afforded my only real view of the city as a backdrop to the park, with a few tall apartment buildings towering over the treetops, at the far side of the Don. A short distance down the trail and the city melts back into the trees, hidden from view, and forgotten, for the moment.

Don River valley

The side trail comes out at a bluff, overlooking a bend in the Don where a gravel bed has been exposed. During my surveys I always scanned the gravel for Killdeer or Spotted Sandpipers, but never saw either, despite it looking like a good spot for them. I did once see a Black-crowned Night Heron fishing from one of the low-hanging trees, but the bend, for all its nice scenery, was always disappointingly empty.

I pause, and look out over the river. The sun is peeking above the trees and casting a warm glow on the bare canopy of the forest across the way. It hasn’t yet reached the river, or even where I’m standing. I briefly consider stopping here, but decide I’d like to sit someplace in the sun, and move on.


The trail goes down a small incline (decline?) and where it levels out it passes through a small grove of spruce. Their lower branches have been pruned from them years ago to make room for trail users to pass through, which gives them an unusually domesticated look, for someplace far from the nearest backyard. In this natural tunnel I recall frequently encountering chickadees, kinglets, and Yellow-rumped Warblers during my spring surveys. There is no one here at the moment.

Northern Cardinal

In other areas, though, the trees are full of song. The cardinals have woken with the dawn, and perch in the upper branches of the poplars, illuminated by the warm orange rays of the rising sun. There are at least a dozen of them, I estimate, throughout the area. They all belt out their declaration of possession of their claimed bits of woodland. “Cheer! Cheer! Whit-whit-whit-whit! … Birdy, birdy, birdy-birdy-birdy-birdy!”

The other birds join in. I hear a pair of White-breasted Nuthatches arguing back and forth at each other over the ownership of a particular patch of cedars, and briefly glimpse a short chase as they dash through a small clearing. A pair of male Downy Woodpeckers has at it over the attentions of a female, who seems rather blasé about the whole episode. House Finches fly over the site in groups of two or three, and I hear the odd male singing. Chickadees move through a patch of hawthorn, calling to one another, and a trio of crows perches atop the maples and caw loudly. The birds seem to be as happy about the sunny morning and approach of spring as I am.

Don River

I come out from the spruce grove along side the river, at a lower area along its banks. The river takes another turn here and is lost from sight, winding its way through the city toward Lake Ontario. It is beautiful here, natural and undisturbed, but along its length it will run through less pristine areas, ultimately coming out through an industrial zone at its mouth before exiting into the lake. A freeway runs north and south through a large part of the valley system, but is far enough away here that I don’t notice it. A rail bed also runs along the valley, and a train thunders by while I’m there. It’s just beyond the ridge, and I can’t see it, but I can certainly hear it. I’ve seen salmon in these parts of the river before, and it seems at odds with the surrounding city, particularly considering the state of the mouth of the river. Nature forges onward.


I decide to take a trail branch that I’ve never been down. On this section of the trail I had always been in the middle of my survey and was unable to follow the side branches. They were often muddy, too, compared to the main trail. However, a few people have been down here recently, and the snow is packed enough to walk along comfortably. I come through another small grove of spruce and the trail widens into a small open area. The sun is streaming in here, and the spruce protect me from the wind. The clearing feels cozy, and I decide this is the spot. I find a log to settle on, and pull out my sketchbook.

I am not ordinarily a field-sketcher. Usually I’m too busy watching birds or taking photos to settle down somewhere and sketch. I admire those who do, though. Debby at Drawing The Motmot is a fabulous field-sketcher. I absolutely love her rainforest studies, which are done in pen while sitting in the field, over as many as three days.

While I have the skill to execute those sorts of drawings, I am sure, I also know I don’t have the practice, or the patience, right now. There’s too much to do, to look at, and I haven’t disciplined myself to sit still long enough to study the landscape and develop the eye necessary to render such detail so accurately. I content myself to sitting for perhaps 20 minutes, soaking up the warm sun, and casually sketching the trail in front of me. Perhaps I’ll make an effort this year to pause more often and sketch a little more.

Sketch of Sauriol trail