The venom from the sting of a wasp contains several toxins. The principal component of venom is a protein — it is the protein that may cause a hypersensitive or allergic reaction in some people. Several different proteins have been demonstrated in wasp venom, the total number and relative proportions vary among the different genera. Other components of venom include an acetylcholine-like substance, histamine, serotonin, and kinin. Kinins are peptides that cause slow contractions of isloated smooth muscle, lower arterial blood pressure, and increase capillary permeability.
The sting of a wasp is rather like two swords lying parallel to one another in a sheath. Each sword has backward-pointing barbs like a fish hook.
The wasp thrusts one of the swords into the victim's flesh, and uses it as an anchor to drive the second sword past it and in deeper. The second sword is anchored in turn to push the first sword further in, and so on. It all happens within a second, and once the sting is embedded well into the victim, venom is pumped into the puncture wound.
The outer sheath of the wasp sting does not have barbs like those found along the edge of a honey bee sting, therefore the wasp can sting repeatedly. When a bee stings a victim, the outer barbs hold the sting in the flesh.