Slugs, slugs, slugs – everybody wants to get rid of the slugs. What about diatomaceous earth? Apparently, the sharp edges in diatomaceous earth cut the bellies of slugs, and they bleed out and die. Diatomaceous earth is used effectively for controlling insects, so maybe it works on slugs. Time for an experiment.
What is Diatomaceous Earth?
Diatomaceous earth, also known as DE, diatomite or kieselgur/kieselguhr, is a soft silica-based rock with particle sizes in the range of 10 to 200 micrometers, or a fraction of a millimeter. The rock consists of fossilized diatoms which are a form of hard algae.
DE is available in two different grades; a food grade and a pool filter grade. For horticultural purposes you should always use the food grade or a product marked for pests. The pool grade is processed differently and will not work.
In horticulture, diatomaceous earth is used as a pesticide. When it is applied to insects, it removes their waxy protective coating, and may cause scratches in their exoskeleton, leading to dehydration and death. If it can kill insects, it might also work on slugs? A lot of information on the internet certainly says it works.
It is claimed that the sharp edges of the diatoms cut the foot (ie the bottom) of the slug, and the slug either bleeds to death or dehydrates due to a loss of moisture.
Warning: slugs and snails were hurt in this experiment and were eventually killed!
Slug Control – Experiment Setup
The experiment is designed to test two things:
a) will slugs (and snails) cross a line of diatomaceous earth? If it were placed around a plant, would it stop the slug from getting to the plant.
b) if a slug crawled across the diatomaceous earth, would it get cut so bad that it dies?
Testing (a) above is fairly simple. Make a ring of diatomaceous earth, and place a slug in the center of the ring. See what happens. If they won’t cross the DE, they will remain inside the circle.
Testing for (b) is a bit more difficult. What do cuts on a slug look like? Do they bleed? I am no slug expert, and don’t have a good stereoscope to check for cuts. I decided I would take a different approach. Let the slug crawl over some DE, and then see if it dies. I don’t really care if they get cuts, or how many cuts they get. As a gardener all I care about is that they die from the exposure.
Collected slugs and snails were kept for a few days in a plastic container with water and some decomposing fruits and vegetables for food. They seemed quite content in their surroundings and were eating well.
Do Slugs Cross Diatomaceous Earth?
The pictures below show some tests to see if snails cross the DE. The experiment was also carried out with slugs and no difference was found between slugs and snails.
When they are placed in the circle they start to crawl and soon reach the DE. Their upper and lower tentacles reach out to sense their surroundings. The upper ones have eyes but they only see light and dark. The lower ones are sensitive to smells. Both are also sensitive to touch.
As the tentacles came close to the diatomaceous earth, they immediately withdrew. Since both types of tentacles withdrew, it seems logical to conclude that they did not like the feel of the DE. Maybe they can feel the sharpness?
In any event, the snails never crossed the DE. When they got close, they turned around and tried to escape by a different route. They did however get some DE on themselves while trying to cross.
The slugs were returned to their plastic home for 48 hours to see what effect the DE had on them. As you can see in the picture below, there were no short term effects.
The test slugs and snails in this trial would not voluntarily crawl over the DE. Provided it is dry and the band of DE is wide enough and thick enough, the DE will prevent the slug from reaching the plant most of the time. In one trial, a snail crawled over another snail, thereby completely missing the DE – he got away.
Does Wet Diatomaceous Earth Work?
Both the packaging and information on the net says that DE is only effective when dry. I repeated the above experiment after dropping some water on the DE. They had no problem walking on wet DE.
Does Diatomaceous Earth Kill Slugs and Snails?
Since the slugs did not cross the DE, I had to find a different way to expose them to diatomaceous earth. I simply picked one up, and dropped him or her (they are hermaphrodites) into a pile of DE. It was forced to crawl on the DE and it got quite covered in the stuff.
It clearly did not like this experiment – did I hear small sequels as the DE cut its belly? I’m not sure. It kept retracting its various body parts, trying to get away from the white powder. Eventually it did get off the pile.
Poor thing! I just picked it up and put it right back on the pile. This time it took longer to get off the pile. The snail did seem to be in some distress or maybe it was just unhappy with its situation. By the time it get free of the DE for the second time, it retracted into it’s shell and just laid there. I figured it was a goner.
The slug was returned to its plastic home for 48 hours. I expected it to die from its lacerations, but as you can see in the picture below, it was fine. You can still see some of the diatomaceous earth on his shell.
I repeated the experiment with a slug to see if there was a difference in survival rate.
Clearly diatomaceous earth does not kill the type of slugs or snails being tested here. Maybe they will die in a couple of weeks, or months from infection or chemical exposure, but as gardeners, if they don’t die fairly quickly, then DE is of no use to us for killing slugs. Diatomaceous earth did not kill slugs in this test.
Diatomaceous Earth Does NOT Cut Slugs
Ever since I read that the sharp edges of DE cut the bellies of slugs, I had my doubts. Slugs are used to crawling all over things. In my post Eggshells Control Slugs – Do They Really Work?, you can see a video of them crawling over knives and raiser blades. Why would a white powder hurt them?
The purpose of slug slime is to protect the foot of the slug from cuts.
While watching the slugs, I noticed that where the slug touched the DE, the DE turned from white to gray. After a few minutes it turned back to white. The gray color is an indication that water/slime had been transferred to the DE. The slime from the slug is making the DE wet and ineffective.
I don’t believe that diatomaceous earth cuts slugs – it is another myth.
Does Diatomaceous Earth Deter Slugs?
I believe it does to a certain extent. If you surround your plant with a line of DE that is as wide as the biggest slug foot in your garden, it will prevent them from getting to your plant. But….. there is always a but.
Rain will wash the DE away and wind will blow it away, so it needs to be applied regularly. When wet, it stops working and slugs like wet places. So don’t apply it after watering or after a rain – you need to let the soil dry out first.
It is not cheap. I don’t think that it is an economical way to keep slugs away from a number of plants. Saving one or two special plants – Ok, but if you try to protect your collection of 40 hostas, you better have lots of cash.
There is one fundamental problem with ringing your plants with DE to keep slugs out. You have to make sure the slugs are not inside the circle, before you put the DE on the soil. If they are, you are caging them in and forcing them to eat the plant you are trying to protect.
Bottom line – DE works to deter slugs, but I question if it is a practical solution for anything more than a couple of plants. In any event it does not kill the slugs.
The Latest Science
The latest testing found that bread dough and bread dough slurry were the best attractant for various species of slugs and snails. It was more effective than beer.
Getting Rid of Slugs and Snails
There are all kinds of methods for getting rid of snails and I have reviewed several of these including:
- How To Get Rid of Slugs and Snails in the Garden
- Eggshells Control Slugs – Do They Really Work?
- Getting Rid of Slugs With Coffee Grounds
- How To Get Rid of Slugs With Beer
- How to Get Rid of Slugs With Copper
- How to Get Rid of Slugs with Diatomaceous Earth
Petroleum jelly, mixed with salt, is a 100% successful slug detergent— IF your garden is in pots. I love your blog (I’m a scientist: love data, loathe rampart internet misinformation). Please spread this solution widely. I’m stunned and ecstatic, because yes, it really IS that easy. In Vermont, my landscape hosts approx 5-10 slugs per sq. foot. Plenty of landscape plants mind a few holes (wildflowers, tall phlox, salvia, geranium, ferns, & even hosta). And of edible plants, aromatics are never touched (sage, rosemary, thyme, mint, chive). Eventually I resorted to putting my entire garden in pots off the ground. Pointless obviously: slugs adore self-watering containers. And mine climb rapidly up bench legs, and stairs to porch. All vegetables and annual flowers consumed entirely. But last few years, Not one single bite! Even petunias. Throw a bit of salt into jar of petroleum jelly, swipe on pot exterior. Or legs of raised benches. A few inches wide suffices. (Don’t forget it’s there!! You’ll be annoyingly cleaning your hands until you remember 🙂 Untouched by torrential rains. One swipe sometimes lasts a couple summers. Just don’t forget to screen the drainage-holes when initially potting. And of course check often for climbable trailing stems or tall grass, otherwise game over. Unbelievably easy & successful. Decades of battling, and countless experiments, solved. Note, surrounding slug density is unchanged. Just, zero in my containers. And best of all: slug predators aren’t effected (like you, I leave all duff habitat). Many equally ecstatic friends are now having exact same experience. Slightly dumbfounded this absurdly easy and cheap solution isn’t all over the internet (SURELY others have thought of it). If you put this in your blog, you might be freeing up the brains of countess container-gardeners to focus on much pleasanter tasks, like creating bee-friendly lawns… or just enjoying their vegetables, lol. Also BTW: one brilliant website (some Canadian extension service?) fixed my mosquitos problem. Black bucket in a leafy shady corner. Add dirty water; top it up as needed, but don’t change it out (attractive egg-laying-hormone-scent gradually increases all summer). Throw in a welcoming stick-ladder. Each week add couple BT crumbles. Voila. All larva in your yard die before hatching.
I would think that petroleum jelly on its own would also be a deterrent?
What are BT crumbles please?