Ant chalk

Ant chalk, also known as Chinese chalk or 'Miraculous Insecticide Chalk', is an insecticide in the form of normal looking chalk. It contains the pesticides deltamethrin and cypermethrin.

While the active ingredients are legal in the United States, the chalk is no longer legal there for a number of reasons including alleged child poisonings reported while the chalk was legal, packaging that frequently does not conform to lead content standards, and inadequate safety labeling.

Despite its illegal status, 'Chinese Chalk' is still imported from China and sold in Chinatowns in the United States. Worldwide, the product remains very popular due to its effectiveness in rapidly controlling crawling household insect infestations without fumes, foul smells or sticky toxic residues, and its relatively low overall toxin content compared to other insecticides.

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Wikipedia