The correct answer is option 1, formic acid. When an insect bites or stings, it injects certain substances into the skin, including formic acid. Formic acid is a common compound produced by ants, bees, wasps, and other insects. It serves various functions for the insects, such as defense or immobilizing their prey.

When formic acid comes into contact with our skin, it causes irritation and triggers an immune response. This immune response leads to the release of histamine, a chemical that causes itchiness. Histamine works by dilating blood vessels and increasing blood flow to the affected area, resulting in redness, swelling, and itching.

While options 2, 3, and 4 are all types of acids, they are not typically found in insect bites and do not cause itching. Acetic acid is vinegar, lactic acid is produced by our muscles during exercise, and maleic acid is not commonly found in insect bites.

It`s important to note that everyone`s reaction to insect bites can vary, and some individuals may be more sensitive to certain insect toxins than others. If you experience severe or persistent itching, it is recommended to seek medical attention.