Does a borax solution kill earthworms?

Yes, a borax solution can be harmful to earthworms. Borax, or sodium borate, is toxic to many soil-dwelling organisms, including earthworms, as it can disrupt their bodily functions and lead to dehydration. While small amounts may not immediately kill them, exposure to borax can ultimately reduce their populations and negatively impact soil health. It's best to avoid using borax in areas where earthworms are present.