flies

While at my parents’ recently, taking photos of dandelions for a previous post, I happened to notice a fly on one of the flowers. It was diving in and burying its head among the petals, I assume collecting nectar. It was a metallic green, small and hairy. I had seen many of these before; I believe they’re greenbottle flies, quite possibly Lucilia sericata, and are a very common species found across the continent.

I decided to see how many different types of flies I could turn up in a quick tour of the property. I’ll add a disclaimer here that these IDs are all tentative, and I may have them incorrect – flies, like many groups of insects, are a notoriously difficult bunch to ID well. They’re easy to tell apart from other insect groups because they only have one pair of wings (unlike bees, wasps, mantids, butterflies, dragonflies, etc, etc, which have two pairs). Flies evolved from a four-winged insect, but their second pair of wings is reduced to vestigial knobs that serve the purpose of stabilizing the insect while in flight (I’m not quite sure how this is accomplished, beyond that it’s a sort of gyroscope effect).

The greenbottles were common. Another common fly was this one, which I think is a flesh fly, perhaps Sarcophaga sp. The group name suggests a connection to animal flesh, and many species do lay their eggs in open wounds or in carrion. However, there are also many that will parasitize invertebrates of many sorts, or will lay their eggs in dung or manure. In the case of this genus, the females lay their eggs mostly in carrion. Blow flies are the first maggots to appear in a roadkill, with the Sarcophaga arriving later. However, the latter will lay live larvae, rather than eggs, to make up for that time difference.

There are 250 species of Sarcophaga in North America, which even though it sounds like a lot, is just a drop in the bucket compared to the total number of dipteran flies on the continent – about 17,000 species, more than the moths I’m attempting to learn, and utilizing a broader set of ecosystem resources – moths generally don’t have much to do with animals, while many flies, as we know, are common nuisances.

One of the things I love about this photo is you can see the sucker pads on the fly’s feet. These are what allow flies to walk along a wall or the ceiling, seeming to defy gravity.

This particular individual was grooming itself, and had its mouthparts exposed for cleaning. Most flies have some sort of sucker-like mouthpart that they use either for sponging up food (such as nectar), sort of in the manner a cat will lick up a bowl of milk, but some have a piercing mouthpart that they use to pierce and suck up their food, such as with biting flies like black flies. Mosquitoes, even though they don’t look it, are actually a type of fly as well.

Despite their reputation for spreading disease, most flies are fastidious groomers. There are some groups that inhabit unsanitary conditions and are attracted to manure, sweat, dead animals, and other things we tend to think of as dirty. However, the majority of flies don’t have much to do with such things, instead frequenting flowers or other food sources. If you watch a resting fly, chances are it will groom itself while it’s sitting there, running its legs over its wings, eyes, and other legs.

One of those flower-visiting flies is this bee fly, probably Bombylius major. They’re named bee flies not for their resemblence to bees (which they superficially do, particularly the bumblebees), but rather for their habit of parasitizing ground-nesting bees. This species is very widespread and relatively common. I watched it for some time visiting the forget-me-nots. It never strayed far from this patch, which was handy, because when I first spotted it I didn’t have my camera on me (I forget what I was doing now, but it was not related to photographing things), and it allowed me to run inside to grab it. It would hover in front of the flowers it was visiting, rather than landing on them to feed.

Many of the “true” flower flies, belonging to the group Syrphidae, are mimics of bees and wasps. This presumably affords them some measure of protection against creatures who would ordinarily view non-stinging flies as a food item. They’re also known in some regions as hover flies for their habit of hovering in front of flowers, but not all hovering flies are Syrphids, and not all Syrphids hover. The group are valuable pollinators of flowers, and the larvae of many species prey on aphids. This one, probably Helophilus fasciatus, I think is likely a male – the females have longer abdomens with an extra black band than the male, and a long black stripe between the eyes that the male lacks.

This fly looks albino, with its overall pink colouration and orangey-pink eyes, but I believe its actually a normally-pigmented member of the myzid fly group, in the genus Suillia. There are 100 species in this family in North America, eight in this genus, but the life cycles of most aren’t well-known. In those where they have been studied, larvae are found in a variety of habitats where animal droppings can be found, such as in burrows, bird nests, or bat caves, or on carrion, dung piles, or rotting fungi.

Crane flies, those long, gangly insects that look like oversized-mosquitoes, are actually members of the Diptera group as well. They’re kind of creepy in their long-leggedness, but are harmless. They are an extremely difficult group to identify beyond family, and even family is tricky, so I won’t try. Like skinks that will lose their tail if threatened, crane flies easily drop legs, so many individuals have fewer than six. Interestingly, there is a group of wingless crane flies that can be found on the snow surface in northern North America in the middle of winter. Larvae are, for the most part, herbivores or detritivores, and can be a major food source for many sandpipers and other shorebirds, especially in the arctic.

And finally, one of our favourites – the black fly. The have the other common name of “buffalo gnats” for their somewhat humpbacked appearance (presumably they would also bother buffalo, along with everything else). They bite people and other animals for the protein in the blood they take, which allows them to develop their eggs more successfully, although most species can produce viable eggs without taking blood. Larvae are aquatic filter-feeders, securing themselves on a rock or piece of vegetation by a sucker-like bit on their abdomen, and using a string of silk to tether themselves should get get swept off (much the way a spider that gets knocked off doesn’t usually fall all the way to the ground). There are 165 species of black flly just north of Mexico, primarily in the north, which amazes me. This particular individual was dead. Partly because it made it easier to photograph, but also partly because it’s hard not to swat at the things when they bite you. They’re the subject of a popular Ontario folk song:

The black flies, the little black flies
Always the black fly no matter where I go
I’ll die with the black fly a-pickin’ my bones
In north Ontario-io
In north Ontario

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.

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.

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.

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.

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.

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.

Tag: flies

Shoo fly, don’t bother me

Tunnels from top to bottom