Ants won’t cross a chalk line: true or false?

Could chalk really be the velvet rope of the ant world? You can’t help feeling someone has just got ants mixed up with demons. In general, a chalk line won’t keep ants out, even if it is part of a pentagram and you stand inside it intoning words of great magick (as the kool kids are calling it now). But — thank heavens, or I’d have to wrap things up here — in the right situation it can work.

There are a couple of pitfalls. First, there is a kind of manufactured chalk containing insecticide that really does keep out bugs. This is just a red herring, though.

What really pulls people off the path to truth is that they aren’t on the right plane of thought. Most of us assume that the chalk line is supposed to stop ants strolling across it if drawn on a path, in a doorway, or on some other flat surface. If you actually try it, though, the ants wander across quite happily. The hasty observer would dismiss the whole think as bunkum right there.

To get at the real truth we need some lateral thinking. Literally laterally, because if we turn the problem on its side we find that chalk can slow ants down on a vertical surface. Ants rely on adhesive pads to climb. When they cross the chalk the powder sticks to the pads and takes away their stickiness. Gravity takes over and the ants come tumbling down.

Well, that’s the theory anyway. French chalk or soapstone, really more like talc than chalk, works well because it makes nice fine powder. But even then if there are enough ants all the loose powder from the chalk line sticks to the feet of the vanguard allowing the rearguard to cross unhindered.

So it’s technically true, in the right circumstances, that a chalk line stops ants. But it’s not really practical. If you’re worried about waking up to find ants in your pants — or, more likely, in your pantry — don’t rely on a chalk line to keep them out.

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