August 17, 2013

Pantry moths, evolution and natural selection

Indianmeal moth (pantry moth)
Note: update at end of post.

You knew those three things would be combined in a headline one day, didn't you? I've been thinking about this lately because my house is plagued in the summer months by pantry moths. They seem to arrive in foodstuffs, though I've never been able to pin down the exact source. In any case, they arrive in Spring and try to live with me until Autumn. (However, I have a BugZooka so the moths end up living outside after I catch and release them.)

Longish post after the jump...
By watching these guys for several years, I've come to marvel at the evolutionary pressures that produced them. Like all insects and most animals, they always do the same things.

When the caterpillar-like early manifestation of the moths transforms into an adult, it launches itself into the air. It's kind of wonderful: the first flight. Here, evolution and natural selection play a dual role. If we observe this first flight, we come to realize that the moth is doing a simple thing: it's looking for a safe place to land.

Every single one of these moths lands on a dark brown surface (which always means the molding at the top of my kitchen cabinets; makes it easy to find them). This behavior is the result of what's referred to as "selection pressure". All it means, in plain English, is that any dark brown moth that lands on a light or -- dog forbid -- a white surface is eaten by predators. Brown on white makes them too visible. Consequently, only the moths that land on a dark brown surface survive and reproduce. And just as your kids take after you, the progeny of these dark-seeking moths will inherit a tendency to land on dark surfaces. It's the only game in town, since moths that don't adhere to this tradition are eaten. Zap; gone.

That's how natural selection works. It doesn't make the moths do anything. It's just that certain behaviors tend to enhance the existence of the moth, allowing it to reproduce and spread its line into the future. This comes about because, over time, evolution causes subtle changes in the moths. And one of those changes produced a moth that seeks dark surfaces. Because of this tiny change, those moths lived and passed the trick on to future generations.

It's not magic; evolution hasn't got a "plan". It's just this: tiny variations occur (as a result of evolution) and combine with selection pressures (hungry insects eating moths that stick out because they land on light surfaces) to produce a rigid behavior that makes the moths seek dark surfaces to land on. This works well for the moths. They win the ultimate evolutionary prize: they are allowed to live and prosper (which means reproduce).

Later (only an hour or so after the first flight, in fact), when the moths mate and produce offspring, they deposit the offspring on a white surface -- because the caterpillar-like babies are white. No moth will ever deposit its offspring on a dark surface. (Or rather, some did in the past, and for this reason did not survive.) I always find the babies stuck to the white ceiling of my kitchen (where I promptly BugZooka them).

It just works. This rigid behavior pattern is what we refer to as instinctive behavior. It's the inevitable product of evolution and natural selection. See? Evolution isn't difficult to understand. It's just common sense, in the end.

I find it glorious that nature works things out in such an organized manner. Mind you, there's far too much death and suffering in this process. After all, the moths without these helpful tendencies are eaten. But in the end, this is the process that produced the world we live in (and us, by the way). It's very cool. And just think: this process makes sense, unlike the silly notion of gods.

Moth image from Wikipedia Commons.

Update: October 14, 2013

I did what Annie suggested -- put my rice and beans in an airtight container. As soon as I did this, all the moths disappeared. Never saw them again.

I hadn't tried this because I once read that you should freeze suspect items, and this would kill anything on it. So I thought the rice and beans had been cleared. I froze them for days. However, they were the source of the moths. This is absolutely confirmed.

The scary thing is that this is on our food. Yuck. And rice and beans, at least the variety that I buy, are in plastic bags. How could anything inside them get out? So is it on the outside of the bags themselves? These days, when I want to use rice or beans I take them out of the airtight storage and immediately wash the bags. Then I wash the contents, and I throw the bag out and bury it in the trash. I have no idea if these measures are necessary, but I still haven't seen a pantry moth.

If you have a problem with pantry moths, I recommend that you put all suspect food into an airtight container. Worked like a charm for me.


Anna Guess Pick said...

eew, don't like that close up Mr. DeMille. I do remember having pantry moths at one time and even seeing moths flying around near the shelves in the grocery store that hold the flour. For years I have kept my various flours in plastic containers or plastic bags, seems to help.

I guess it all boils down to just having to get along.

writenow said...

I should try that. I cleaned out all the cabinets. Made no difference. They seem to materialize from thin air.

Speaking of insects, when I went for a walk this morning the trees were filled with male cicadas, all singing madly. Given their late arrival, I assume this is the Brunch Brood.