A stinger, or just sting, is a sharp organ found in various animals (typically arthropods) that delivers venom (usually piercing the skin of another animal). A true sting differs from other piercing structures in that it pierces by its own action and injects venom, as opposed to teeth, which pierce by the force of opposing jaws. Stinging hairs which actively inject venom on plants such as stinging nettles are also known as stings, but not stingers.
An insect bite and sting is a break in the skin or puncture caused by an insect and complicated by introduction of the insect's saliva, venom, or excretory products. Specific components of these substances are believed to give rise to an allergic reaction, which in turn produces skin lesions that may vary from a small itching wheal, or slightly elevated area of the skin; to large areas of inflamed skin covered by vesicles and crusted lesions.
Stinging insects produce a painful swelling of the skin, the severity of the lesion varying according to the location of the sting and the identity of the insect. Many species of bees and wasps have two poison glands, one gland secreting a toxin in which formic acid is one recognized constituent, and the other secreting an alkaline neurotoxin; acting independently, each toxin is rather mild, but when they are injected together through the stinger, the combination has strong irritating properties. In a small number of cases the second occasion of a bee or wasp sting causes a severe allergic reaction known as anaphylaxis.
Hornets, some ants, centipedes, scorpions, and spiders also sting. Some insects leave their stinger in the wound. Multiple stings may give rise to severe systemic symptoms and in rare instances may even lead to death; the bites of some spiders are known to be lethal, particularly to young children.
The main type of construction of stings is a sharp organ of offense or defense, especially when connected with a venom gland, and adapted to inflict a wound by piercing; as the caudal sting of a scorpion. The wasp has a very painful sting, and will sting if it feels threatened.
Unlike most other stings, honey bee workers' stings (a modified ovipositor as in other stinging Hymenoptera) are strongly barbed and lodge in the flesh of mammals upon use, tearing free from the honey bee's body, leading to the bee's death within minutes. The sting has its own ganglion and it continues to saw into the target's flesh and release venom for several minutes. This trait is of obvious disadvantage to the individual but protects the colony, comprising many sterile workers who are all sisters, from attacks by large animals; the shared genes of the colony are more likely to be passed on if it is defended vigorously. The barbs ensure that a honey bee's attack is only suicidal if the attacker is a relatively large animal; bees can sting other insects repeatedly and without dying. The sting of nearly all other bees and other stinged organisms is not barbed and can be used to sting mammals repeatedly. The stingers of yellowjacket wasps and the Mexican honey wasp are so small that they do not cause the sting apparatus to pull free. The stingers of some wasps, such as those of the Polistes versicolor, contain relatively large amounts of 5-Hydroxytryptamine (5-HT) in its venoms. The 5-HT in these venoms has been found to play at least two roles: one in defense as a pain-producing agent and the other in the distribution and penetration of the paralyzing components to vulnerable sites in the offender. This helps in the rapid immobilization of the animal or of the certain body parts of the animal receiving the venom. 
Organs that perform similar functions in non-arthropods are often referred to as "stings", although they are all technically considered to be something else (e.g., a venomous barb). These include the modified dermal denticle of the stingray, the venomous spurs on the hind legs of the male platypus, and the cnidocyte tentacles of the jellyfish.
In plants, the term "sting" is normally used as a verb, but occasionally used as a noun refer to urticating hairs; sharp-pointed hollow hairs seated on a gland which secretes an acrid fluid, as in species of Urtica (nettles). The points of these hairs are brittle and break off easily, leaving a sharp point like a hypodermic needle, through which the fluid is injected. On the other hand, the bristles of some cactuses are recovered by retrorse barbs (like the foxtail spikelets), preventing the fall once they are stung, and they are called glochids.
- Oxford English dictionary, 2nd ed., sting n2, 3
- Thomas Eisner, Maria Eisner, Melody Siegler (2005). Secret Weapons: Defenses of Insects, Spiders, Scorpions, and other Many-legged Creatures. Harvard University Press. ISBN 978-0-674-01882-2.
- Welsh, John H., and Carolyn S. Batty. "5-Hydroxytryptamine Content of Some Arthropod Venoms and Venom-containing Parts." Toxicon 1.4 (1963): 165-70. Web.
- Oxford English Dictionary, 2nd ed. "Sting ... Applied also to the fang or venom-tooth (and erroneously to the forked tongue) of a poisonous serpent."
- Nicholas Stephens (2006). Plant Cells and Tissues. Infobase Publishing. p. 102. ISBN 978-0-7910-8560-8.
- Media related to Stingers at Wikimedia Commons