Diatomaceous Earth and Bees

Honey BeeThis effective, organic pest killer (it’s not a poison) won’t hurt bees if used wisely.

Who hasn’t been bailed out by diatomaceous earth, basically a powder made of fossilized diatoms millions of years old? Keeping armies of slugs at bay, drawing a no-roach line between our apartment and our neighbors’ apartments, protecting seedlings from early season grubs and maggots. I’ve known people who’ve rubbed the stuff into their dog’s coat to stop fleas and heard that’s it’s a common big-city cure for bed bugs.

Diatomaceous earth has something of a miracle-cure reputation and it certainly is effective against many pests. It’s not a poison, but kills by scoring an insect’s hide as it crawls over the powder. Under the microscope, that powder looks like a pile of broken glass. There were suggestions that diatomaceous earth was an effective anthelmintic (a sort of cleanse, popularly known as worming) for sheep and goats, but a series of studies proved this not to be true.

Back when, trying to combat insect damage to my vegetables without the use of harmful chemicals, I heard DE was safe enough to eat. And, in a way, it is if bought as food-quality. But much of it isn’t and might even be dangerous if ingested. DE sold for pool maintenance and other filtering uses may have additional contaminants, including chlorine. It’s also been heated which concentrates its silica content. Much of the diatomaceous earth sold as OMRI listed (for organic use) is 75% silica or above. It contains naturally occurring remnants of crystalline silica, as fine as powdered beach sand. Like any mineral dust, you wouldn’t want to inhale it. Of course, there’s food grade diatomaceous earth that’s both recommended as a supplement for its healthy silica content and as an insect barrier around the house or in the garden.

Diatomaceous earth works wonders on larvae, maggots, and grubs; anything that crawls over it. How many times have we kept slugs off our favorite plants with a circle of DE flour? It addition to its Jack-the-Ripper reputation on crawling bugs, it also works as a repellant on flea beetles and grasshoppers. And no, it doesn’t cut your fingers when you use it. It feels like chalk. But then, you’re not an insect. (You may still need to wear a mask when applying it.)

Pest Problem SolverBecause DE is so effective, we have to ask about its effects on honey bees and other pollinators. While it turns out the bees have some defense against the powder — those furry hairs that cover much of their bodies — DE is neither good for them or a desirable thing to have taken back to the hive. But that doesn’t mean it can’t be used cautiously with the bees in mind.

Pauly, over at Worm Farming Revealed, checked out the possible diatomaceous earth exposure and dangers to honeybees and concluded that knowing a few things about bees and DE takes away most of the risk. He cites Tui Rose’s book Going Green Using Diatomacous Earth How-To-Tips on how bees are protected: “When Diatomaceous Earth is applied to crops or orchards, the honey bee tends to protect themselves by simply avoiding those blossoms already treated with DE. However, if DE does get on a bee’s body, it is covered with slick hairs that are able to help prevent dehydration of body fluids.”

We can’t confirm that bees avoid DE. The body hair theory makes perfect sense. (Amazingly, earthworms aren’t harmed by diatomaceous earth. They’ve got that slick gooey mucous layer that helps them slide through the soil.) But, Pauley, in his wisdom, comes up with the best advice: “It is my opinion that diatomaceous earth should only be used when necessary to eliminate an over infestation of pests in the garden.”

Others have suggested that proper application of Diatomaceous earth can cut down on the risk to bees and other pollinators. If you can, avoid using it on or near blossoms. You know where the bees are headed. Give’em a break. Also, apply, be it spray or broadcast, when bees aren’t active. This means applying in the evening as bees move back to the hive for the night. I’ve seen some sources suggest that morning is fine, too, and preferable because it will utilize the morning dew to capture the DE. But bees get active early in the warm summer months. They’ll be arriving, if not during spraying, then before the moisture has a chance to evaporate and leave the DE harmless to bees.

To his credit, Pauly has gone for a second opinion and its not encouraging. He spoke with David Burns of Long Lane Honey Bee Farms in Fairmount, IL who blogs at Honey Bees Online: “DE controls insects by cutting their exoskeleton and unfortunately bees fall in that category. Not good for honey bees. They will attempt to groom off the DE and thus it will do its job on honey bees too. Sorry.”

So we have somewhat conflicting accounts. There’s always something that needs to be weighed in the balance between harm and good, even in the world of organic gardening. I’ll go out on a limb here and say that I personally would rather not use diatomaceous earth if my use will harm bees, even in small numbers. Bees are in crisis now and we need to protect them all.

Still, I’d use DE on the ground to keep slugs away. And I’d consider spot usage say if a pepper plant suddenly harbors clots of aphids. See? I’ve already made exception to what sounded like an absolute decision. Used with care and consideration for bee activity, DE is still, in my book, the miracle cure. Let us know what shade of gray you are on this issue, here in comments (way) below, or on Facebook. (hasn’t that been an interesting place lately?). And be sure to tell us the extent and kind of the insect problems in which you’d employ diatomaceous earth. Anybody taking it as a supplement?

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