This belief may come from an idea that a praying mantis can spit a poison at you, but this is not true. Walking
What is the black stuff that comes out of a praying mantis?
Chordodes formosanus is a horsehair worm that has the praying mantis as its definitive host. Horsehair worms are obligate parasites that pass through different hosts at various stages.
Can a praying mantis hurt you?
Clearly, these insects are voracious predators, but can a praying mantis hurt a human? The short answer is, it's unlikely. Praying mantises have no venom and cannot sting. Nor do they carry any infectious diseases.