Dry weight

There have been ants in the kitchen for a fortnight, which is the December tax in this house, and on Saturday I went to the garden centre to do something about it.

You can buy a bag of dead algae for about fourteen dollars.  It’s on a shelf between the snail bait and the slug pellets, in a paper sack with a picture of an ant on it, and the small print on the back calls it diatomaceous earth.  Nobody involved in selling it to me appeared to find this remarkable.

I have known what diatomaceous earth is for as long as I’ve worked with these organisms and I still stood in the aisle for a moment holding the bag.

In the hand it’s a very fine pale powder, somewhere between talc and flour, faintly cool, and it gets absolutely everywhere.  It has that quality some powders have of appearing to be slightly more than the volume of the container it came out of.  I tipped a little into a dish on the bench and by evening there was a thin film of it on everything within about half a metre.

Under the microscope it stops being powder.

It’s a boneyard.  Whole shells, split halves, fragments, the occasional intact cell wall sitting there with its pores and ribs perfectly legible, the same architecture you see in a drop of harbour water except that none of it has been alive for a very long time.  Rows and radials, edges that are obviously manufactured.  Some of it is recognisable enough that a person who does this for a living could put a name to it.

I’d assumed for years, without ever bothering to check, that this was basically the same material as the white cliffs you see in photographs of the English coast.  It isn’t.  Those are made by a different group of microscopic organisms that build their plates out of calcium carbonate - chalk, essentially, the same stuff as limestone and antacid tablets.  Diatoms build out of silica, which is glass.  Two entirely separate lineages arriving at the same idea of an armoured single cell, out of different materials, and leaving behind two different kinds of rock.  I had them filed under one heading for a decade because they are both pale and both very old.

The deposits get quarried on land, out of places that used to be seabed or lakebed, in beds thick enough to be worth digging up with machinery.  Which means that for a period long enough to lay down a quarry, cells were being built and sinking and being built again, in numbers that don’t really submit to being imagined.

The reason it kills ants is the part I find genuinely unsettling.

It isn’t a poison.  There’s nothing chemically active in it at all.  Insects have a waxy layer on the outside that keeps water in, and the powder gets into the joints and abrades that layer, and after that the animal simply dries out.  It’s a mechanical death.  The glass is still sharp.

That’s what I keep circling.  Not the age of the deposit, which is easy to say and impossible to feel, but the fact that the structures are still doing work.  The organism has been gone since before there was anything you’d recognise as a landscape here, and the thing it built is still hard enough and fine enough to cut a beetle’s cuticle open in a kitchen in Auckland in December.

There’s an industrial version of this too.  In the nineteenth century, when nitroglycerin was killing the people trying to handle it, the fix that eventually worked was to soak it into an absorbent powder so it could be moved without detonating.  The powder was diatomaceous earth.  That’s dynamite - and a decent share of the money behind the Nobel Prizes came out of it.  Every year, in a hall in Stockholm, someone gets a medal for the best work in physics, and the endowment traces back through a patent to a quarry full of dead algae.

A practical note, since I looked it up and was mildly alarmed.  The garden grade is the raw stuff and is fine to handle sensibly.  The grade sold for swimming pool filters has been heat-treated, which changes the silica into a form that is genuinely bad to breathe.  Either way, don’t stand in a cloud of it.  I wore a mask for the microscope work and felt slightly silly, which is the correct amount of silly.

The bag is under the sink now, mostly full.  The ants have thought better of the kitchen.

Fourteen dollars, and the receipt is still in my pocket.