Keep ants at bay by drawing a line around home entry points. The ants will be repelled by the calcium carbonate in the chalk, which is actually made up of ground-up and compressed shells of marine animals. Scatter powdered chalk around garden plants to repel ants and slugs. (src: 13 Common Items for Getting Rid of Ants)

Is there scientific research refuting or backing up the "The ants will be repelled by the calcium carbonate in the chalk" part, or the whole approach of pest control via chalk?

  • calcium carbonate is Lime which is mixed with many fertilizers or as a standalone product. Its purpose is to neutralize acidic soil though not prevent bugs. – Ryathal Feb 21 '13 at 18:21
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    Its the same substance, sidewalk chalk is just pressed into a larger block and may include coloring agents, if it actually worked to prevent ants and slugs it would be advertised as such – Ryathal Feb 21 '13 at 18:34
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    Does someone have an ant problem and is looking for a way to fix it or something? Two phobia of ants related questions in such a short time span. :P – Wertilq Feb 22 '13 at 0:38
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    Searching the internet reveals that a huge number of substances supposedly repel ants if you make a line with the substance: salt, chalk, vinegar, lemon juice, coffee grounds, cinnamon, etc. A line of anything will temporarily disrupt ants' scent trails. I am skeptical that any of these substances have any long term effect, though. – user11522 Feb 22 '13 at 15:00
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    Sounds like they're confusing chalk with Diatomaceous earth, which is made of shells of marine microorganisms and kills insects. Wikipedia says it kills through drying, though I'd heard it kills by cutting them. – endolith Mar 4 '13 at 19:24

This may be a bastardization rumor referencing "Chinese Chalk" (or "Miraculous Chalk"), special insecticide-laced chalk which can be used to block the paths of insects. I have heard of overseas restaurants using this chalk to draw lines on the legs of tables, preventing bugs from climbing up the table legs. It is a banned substance in the United States due to

  1. potentially unknown insecticide used in the chalk
  2. people using it barehanded when it is potentially unsafe to do so
  3. children mistaking it for actual chalk

The phrase "made up of ground-up and compressed shells of marine animals" definitely describes the chalky, white powder commonly referred to as "diatomaceous earth". Diatomaceous earth sticks to the carapace of insects and is as sharp as broken glass at their microscopic level; it is frequently used to get rid of bed bugs.

Chinese Chalk may be made of a combination of diatomaceous earth and deltamethrin, a combination which is marketed in powder form as the insecticide Delta Dust. I've used it effectively (with a duster) to stop existing / prevent further white-footed ants, but diatomaceous earth itself might be sufficient alone. While I have never tried to compress them into stick form, both Delta Dust and diatomaceous earth are chalky, white powders, and may be applied with a paint brush, the results of which could appear to emulate a chalk line.

  • I'm not sure that that product placement is entirely appropriate as it doesn't address the question. – Ian Mar 5 '13 at 11:22
  • I have no vested interest in the product. The original asker is looking at ways to prevent ants; let him tell me it's inappropriate and I'll remove it. – JoshDM Mar 5 '13 at 14:59
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    Skeptics is not about recommending solutions, it's about investigating specific claims. In this case the claim is specifically about whether ants will cross chalk lines. Alternative non-chalk-based products (such as Terro) have no place in this answer unless they specifically relate to ants behaviour. And the asker is not the ultimate authority on this matter; all content on this site belongs to the community and as such must comply with community guidelines, not what you or the asker thinks is best. – Ian Mar 5 '13 at 16:46

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