Which observation supports the hypothesis that fire ants produce a substance that is harmful to humans?

The observation that fire ant bites cause pain directly supports the hypothesis that fire ants produce a harmful substance to humans. This is because the pain associated with a fire ant bite is a result of venom that they inject into their victims. The presence of pain signals that there is a physiological reaction to the substance introduced into the body during the bite, implying that it has harmful effects. In this context, the pain serves as clear evidence that the secretion from fire ants can be detrimental to human health, aligning with the hypothesis.