From Lutz U

Bad Nature 101: Cluster Fly

Dear Devin,

Hello. How are you? Happy holidays and all of that. I have a few bug/tree questions that I'm hoping you can answer. I know you're not an entomologist or an arborist, but I'm sure you'll have some insight into my problem, since you're a scientist.

Lisa's X'mas Tree BeforeAbout a week ago, I went to a local Christmas-tree farm and cut down my own tree. It was a great deal: $45 for any size tree, if you cut it. I didn't pick a small one, so it took some labor getting through the trunk, but I managed. I brought the tree home, got it in the stand, and decorated it with little bottles of booze and lights. It looked awesome.

Then I noticed a smell. I'm not sure how to describe it. It wasn't good tree smell, but a nature smell. Bad nature. Sometime after I noticed the smell I started to get cluster flies in my house. Lots of them. One morning, before I even had any coffee, I killed about seven flies. I'm sure you've seen them before, but I'd like to emphasize how disgusting they are. They're like regular flies, but under a magnifying glass.

Anyway, when the flies kept coming, I decided that the timing of the tree and the unwelcome intruders was not a coincidence, and I made the very difficult decision to abandon the tree. Although I have to admit that when I was moving the tree outside, I didn't smell bad nature at all. Just tree.

After the tree was gone, I had to hunt down another dozen or so flies, but now they seem gone. I don't have the cluster flies anymore, but I also don't have a Christmas tree (please no comment about me being Jewish).

My questions: Did my balsam fir bring in the cluster flies? Did I toss my tree for nothing? And what do you think that nature smell was?

After spending several days observing and exterminating these things, I have to wonder what's the point of them. They seriously do nothing. They just loll about on windows waiting to be assassinated. What is their place in the whole food chain continuum?

Any information would be greatly appreciated,



First off, apologies for the delayed reply. Now that it is after Christmas, all of this is a moot point, because you would be throwing out your tree about now anyway. Part of it is that I have been very busy—this being the end of the semester and year. Another part of it is that for many tasks, if you ignore them for long enough they end up going away. I find this an essential strategy for coping with the demands of life and work in middle age.

cluster flyAbout the flies and the tree. A first question to ask is: Do you really know that they are cluster flies? There are over 200,000 species of flies, and differentiating between them often involves looking for small differences in wing venation and other subtle traits. Cluster flies hatch from earthworms, so it seems unlikely that the flies would be hatching out of your tree. The flies could have simply been hiding in the tree—however I would have expected you to notice large clusters of the flies while hanging your mini bottles. So if they were truly cluster flies, it seems to me that you may have tossed your tree unnecessarily. You just happened to bring in the tree at the same time that lots of the flies were looking for a nice warm place to spend the winter.

However, cluster flies are in the family Calliphoridae: "blow flies." Your tree could have been infested with a related species of Calliphorid, which commonly hatch from carrion, dung, or other nasty stuff. This could also be an explanation for the "bad" nature smell. In which case, your tree may have had an unnoticed dead bird or turd, that, depending on its size, might have justified the tree's disposal.

So, knowing the specific fly you were dealing with is essential.

The second question to ask is how you feel about the flies, and the smell. Starting with the smell. For me, bad smells are from things that can make you sick. Yes, this includes some natural things like carrion and feces. But most natural smells are from things that are not dangerous and therefore not bad. In contrast, many manmade things can and do make you sick (i.e. cleaning products, new upholstery, vehicle exhaust, etc.). Therefore, I would apply the term "bad nature" to a very small subset of natural smells, and ask you to ask yourself if you really meant "bad" or perhaps instead simply meant "unidentified."

Similar thinking can be applied to the flies. Yes, we are justified in worrying about a very few species of flies because they can vector diseases. However, this does not mean that most flies (or insects for that matter) are dirty or dangerous. Insects are much less of a risk to us than other people are, even people we very casually encounter. Moreover, flies are magnificent creatures any way you want to look at them: extreme performance fliers, ultra-bad-ass survivors, paragons of design simplicity. If you really look at them, they are more beautiful than the tree itself (although they probably don't smell as good). With a little attitude adjustment, you might have been able to see your guests in a different way, and kept the tree.

If you insist on clinging to irrational fears and detesting the flies, you could have used them as an outlet for your violent impulses, as they were relatively easy to kill. They were probably low on energy, cold and starving anyway. I have seen pictures of your thermostat and can guess there isn't much edible lying around your house.

Or, you could have simply ignored the flies. If they were coming from the tree, then there must have been a finite number. If you had waited long enough, the problem would probably have gone away.

Anyhow, that's my thinking on this. I certainly wouldn't presume to tell you what to do, or what you should have done. That you made the choice and then felt it necessary to find some support for it I think speaks for itself.




Lisa's Xmas Tree AfterYour reply seemed kind of cranky. You getting enough sleep? You're right, the point is now moot, but there are still things to be learned for future reference. Since you were really tardy with your reply, I asked my exterminator about the possibility that the cluster flies and the tree were connected. He seemed to think that was a distinct possibility and also didn't challenge me on my opinion of flies or cluster flies or whatever.

My feeling about exterminators and firefighters is that they are not ridding the world of things they hate, but things they love. So, firefighters must really like fire, to want to be around it all the time, and exterminators must be fascinated by pests for the same reason. Still, my exterminator thinks that flies are the worst. Don't get me wrong, I'm okay with them being outside and dealing with decomposition and stuff, but in my house, no.

Let's get another thing straight: I don't have an irrational fear or even a fear of flies. I just don't see why I need to share my home with them. Also, there's no way there was a dead bird in my tree and I didn't notice it.

Let me end this on a positive note. Right now it is about minus eight degrees in these parts, which means that most flying pests are beyond dead. Maybe next year I'll wait until a deep freeze before I bring home my hand-sawed tree.

Thanks again, Devin, for your thoughtful and mildly hostile response. I look forward to seeing you sometime in 2014.

And Happy New Year to all,

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