Insects have many enemies, including birds, lizards, small mammals, spiders and most dangerous of all, other insects. In order to put off attackers, insects have many different defenses. Some insects use weapons. Others rely on flight, concealment, motion, armor, and even grotesqueness. Some really interesting insects use powerful chemical warfare.
Bees, wasps and many ants have powerful stings. Some of the poisonous chemicals they inject into attackers can be very painful. Some ants can fire an acid fluid from their rear ends. If you disturb a nest of wood ants, you'll be able to smell the acid as the ants rush out and spray it in all directions.
The bombardier beetle sprays a boiling-hot and poisonous mixture which can cause painful blisters to form on the skin (ouch!). Many insects can put off would-be attackers by producing chemicals that taste horrible. Ladybirds, for example, give out a foul-tasting yellow fluid if they are attacked. Some of the fluids given off by insects are quite poisonous. Many caterpillars are covered with irritating hairs which make attackers let go of them.
Bombardier beetles store two separate chemicals (hydroquinone and hydrogen peroxide) that are NOT mixed until threatened. When this occurs the two chemicals are squirted through 2 tubes where they are mixed along with a small amounts of catalytic enzymes. When these chemicals mix they undergo a violent "exothermic" (as chemists would call it) chemical reaction. The temperature of the resultant sprayed mixture exceeds 210 degrees F.