Discovering Diatomaceous Earth
Diatoms as seen through a microscope. Note their stained glass window shapes and silica bodies (Photo: Wiki Commons).
To Use or Not to Use, That is The Question
As Spring infestations of pests, fleas, and insects begin, many homeowners are faced with how to control these critters, either in the home, garden, or even on pets. If you're like me, you'd rather stay away from chemicals all together. There are many different natural solutions out there for different organisms, but it's difficult to tell what works and what doesn't. In coming posts I'll explore some of these solutions, but I want to start with Diatomaceous earth.
Diatoms are a type of microscopic aquatic plankton or algae (2-200 micrometers in size). They are small photosynthetic plants. We owe almost every other breath that we take to these numerous wee producers that are respiring in our lakes, rivers, and oceans. Their shells are made up of silica and calcium carbonate. In essence, they look like tiny stained glass windows.
Pictures of diatoms under the microscope (Photo: Wiki Commons).
Their bodies are made like a gift box, with a top that slides over a bottom. When they reproduce, their two halves separate and then regenerate a new half. In the oceans, they are estimated to provide nearly 1/2 of all the primary food production for aquatic life! They've been around for a long time, all the way back to the Jurassic. Their glassy bodies have been floating around providing oxygen and food for millions of years. As these small organisms die, their glass bodies either sink to the bottom of the ocean or become sediment deposited on shorelines. When you look at sand under a microscope, you'll often see tiny grains of rock, but you'll also see the remains of diatoms. The main ingredient in making glass is silica, which is added in the form of sand. Guess who provided all those bits of silica? Diatoms!
Diatomaceous earth, or diatomite, is made up of the sedimentary deposit of fossilized diatoms deposited over millions of years. They are usually whitish and abrasive feeling because of the nature of the silica, though the food grade kind may feel as soft as talc. It is very light because it has a high porosity and it is not combined with all the other heavy elements of rock and sand that are found in sedimentary sandstone.
Diatomaceous earth has been used in a variety of industrial settings, including for filtration, reinforcement of plastic, abrasion for tooth pastes, fillers for rubber and cat litter, and even stabilizing dynamite. One of its more common uses is as an insecticide.
Diatomite from a mine in CA (Photo: AlishaV. Flicker)
As a pesticide, diatomaceous earth must be unheated or calcified (which is often done to increase its filtration value). Calcification burns or melts the silica, reducing its efficacy. If you were to look at diatomite under a microscope, you would see startling edges. These glassy edges are sharp as razors to invertebrates, but won't hurt humans or large animals. This is why it has been touted as a natural pest control. Before you get too excited though, let's really examine what it does to control all of these "pests."
Diatomaceous earth acts as a very strong cutting abrasive on the exoskeleton of invertebrates, including bed bugs, fleas, ticks, worms, slugs, and all six and eight legged insects. It is essentially the "death of a thousand cuts." Those cuts open up the organism to dehydration and infection within 24-48 hours, causing death. The other property of diatomaceous earth is that it is absorptive. It acts to dry out and desiccate the microorganisms that are cut by its sharp edges. So, how is this bad you ask? Diatomaceous earth is a generalist. When you apply it to your garden, you are in turn, not only killing the harmful slugs, grubs, roaches, silverfish, aphids, and thrips, but you're also killing all the beneficial insect life as well. This includes earthworms, pill bugs, ants, beetles, ladybugs, beneficial caterpillars, and more. This generalist approach is detrimental to the ecosystem, though perhaps less so than most chemicals. The other down-side to diatomaceous earth is that it loses its potency once it rains and the diatoms clump together. It has to be applied during dry days without rain.
Beneficial jumping spiders may be negatively impacted by diatomaceous earth (Photo: Karen McDonald).
As with all pesticides, you have to consider the ramifications of using it in your garden or around your home. Yes, diatomaceous earth is mostly harmless to humans and pets (with a few exceptions of inhaling etc., and it is a controlled substance through the USDA), and yes, it can be quite effective in killing grubs and other garden pests. However, it's a generalist and like other chemicals, it kills everything indiscriminately. On a microscale, I can only imagine the "gory movie scenes" of what really goes on in the undergrowth and below ground once it is applied. I can picture the razor like edges cutting the microinvertebrates and their slow desiccating deaths. I have my own opinions, but everything has a cost and must be weighed. What do you think? Would you use it? Have you used it?