The most poisonous insects in the United States are wasps, hornets, bees and fire ants. While no American species is toxic enough to kill a human being with the amount of venom a single sting releases, all of these insects are dangerous to people who are allergic to their venom.
The most dangerous insects in the United States are hornets, yellow jackets and Africanized honey bees. All of these insects live in colonies and are quite aggressive, meaning that a human who encounters these insects may be stung many times before he can get far enough from the nest that the insects no longer pursue him. Fire ants have similar characteristics but are easier to escape because they can't fly.
The United States is also the home to a number of poisonous arthropods, invertebrate animals belonging to the same phylum as insects. The most dangerous are the black widow and brown recluse spiders, as well as the Arizona bark scorpion, all of which have venom potent enough to kill a human being. However, fatalities are rare. Tarantulas and centipedes are less dangerous with a bite comparable to an average wasp or bee sting.
Allergic reactions are the greatest cause of death for people stung or bitten by poisonous arthropods. Indicators of an immediate need for medical attention include intense swelling at the injury site, swelling of the throat and difficulty breathing.