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The Bottom Line
The tiny creatures that sometimes appear in toilets after heavy rain are often mosquito larvae or other small aquatic insects, especially when standing water and plumbing conditions allow mosquitoes to breed. While the sight can be alarming, it usually points to an environmental or plumbing issue rather than something mysterious or dangerous.
A little investigation—and a few preventive steps—can usually solve the problem and help keep your bathroom pest-free, even after the heaviest storms.