Wasps are any animal in order Hymenoptera and suborder Apocrita that is neither a bee nor ant. There are over 200,000 species, making wasps one of the most diverse groups of insects. The most familiar types are the common wasp (Vespula vulgaris), yellowjackets (members of genera Vespula and Dolichovespula), and the European hornet (Vespa crabro). These animals are generally categorized at the highest level by whether they are social or solitary. The group probably evolved in the Triassic Period, about 225 million years ago.
Like all other insects, wasps are invertebrate arthropods that reproduce using a larval stage. They have two pairs of wings used for flight. Females have a stinger, which evolved from a female sex organ called an ovipositor, thus being absent in males. Most wasp stings are painful and unpleasant, described by the entomologist Justin O. Schmidt as "like a matchhead that flips off and burns on your skin." A few rare species, like the Asian giant hornet, can produce stings so toxic that they can kill. The sting of the Asian giant hornet was described by one Japanese entomologist, Masato Ono, as being "like a hot nail being driven into my leg." Unlike bees, wasps lack barbs on their stingers, meaning they can sting repeatedly.
Both wasp adults and larvae are the leading parasites in the insect world, and there is a wasp parasite for practically every pest insect, making them very useful for pest control. The larvae are parasitoid, meaning they are parasites during the larval stage. About 10-20% of insects are parasites, but wasps make up the majority by far. Some are parasitic in their adult forms as well, but these tend to be small, 1/100 to 3/4 of an inch long. As a result, they mostly tend to go unnoticed by humans, though they kill many pest insects.
Wasps that aren't parasitic build nests. This includes both predatory asocial and social wasps. Both types build nests out of paper created by chewing wood pulp and mixing it with saliva. They choose sheltered areas such as attics or holes in the ground, with direct access to the outdoors a must. The nests have little cells for laying eggs in. Asocial wasps lay the eggs and leave them, while the social type continue interactions as the eggs turn into larvae and then adults.