Typically wasps tend to be more aggressive and will gravitate towards human food more so than bees. Bees are seemingly more gentle in nature and are a lot more interested in flowers that your food. If you find yourself stung your logical assumption can be that your attacker was a wasp.
In the instance that you do not see the insect, you can inspect the site itself for more information. Both bees and wasps inject a venom with a stinger that is attached to their bodies. Most wasps and bees can inject the stinger into your skin and remove it before flying away, except for the honey bee. A honey bee’s stinger is barbed and it sticks to a human’s skin after being stung, therefore when a honey bee tries to fly away, it cannot do so without ripping the stinger from its body. The stinger is attached to the honey bee’s digestive system and as a result the honey bee will eventually die from the experience.
For more information please go to the following site: http://www.emedicinehealth.com/bee_and_wasp_stings/article_em.htm