While insect bites and stings are an unfortunate event in life, they usually only cause mild irritation. For instance it is normal after getting stung by a hornet on the forearm to have some pain, swelling, itching, and redness at the site. It is not normal, however, to have swelling, redness, and pain of the entire forearm or arm that remains for several days. It is also not normal for someone to have swelling of their throat, develop hives, develop difficulty breathing, vomit, or lose consciousness after a sting. Worse yet there are estimated to be around 50 people that die each year from stinging insects.
In the U.S. there are certain species that cause the majority of these issues. These in include honey bee, wasp, yellow jacket, and hornets that are present in most of the country. In the southern U.S. another culprit is the fire ant. While other species can cause severe allergic reaction these are the most common instigators.
It is impossible to predict when someone will be stung (except possibly for high risk occupations such as beekeeping), so it is imperative for those that have more severe reactions to be prepared for such an event. This includes a rescue medication and seeking emergency medical aid. There is also a proven treatment that can be 98-99% effective in preventing severe reactions.