Kill wasps in the air by spraying them with wasp spray; hosing them will only make them more aggressive. Since wasps and hornets aggressively defend their nests, the safest method of destroying nests is to call a professional exterminator or wait until October when the queen insect has left and the workers have died. At that time, if nests are aboveground and hang from trees or houses, you can dislodge them with the spray from a hose. If the nests are in the ground or inside a wall, you can dig them up or out.
Seek immediate medical attention for anyone who is stung and allergic to wasp or bee stings or is not allergic but stung around or within the mouth, nose, or throat, as swelling could close airways. Otherwise, take out the stinger: Dislodge it by scraping across it with a credit or playing card. Do not pull the stinger out by gripping it with tweezers or your fingers, as you could force more venom into the wound. After the stinger is removed, wash the area. A paste of baking soda and water can lessen pain. Ice will reduce swelling.