Tracker Jackers are genetically engineered wasps, conceived and created in the Capitol. They are genetically coded to attack anyone or anything that disturbs their nest. Once they make a person their target, they will follow him or her far away from their nest, unlike natural vespids. Tracker jackers were used as weapons during the war and planted around the districts of Panem. After the Dark Days, the Capitol destroyed some hives around themselves, but still kept the hives around the districts as a cruel way to show their power over the inhabitants. Tracker jackers look like normal wasps, except for their larger size and golden coloration. One or two stings can cause powerful hallucinations, but several stings can lead to death of the victim. Tracker Jackers are used by the Capitol to keep people out of restricted areas in the Districts.
The swelling caused by the stings commonly range from the size of a plum to the size of an orange, and reach their full size only a few minutes after the initial sting. If the barbed stinger is torn out, the entry hole oozes a foul-smelling green liquid. It is unknown whether or not the green liquid is real or not, as Katniss is hallucinating at the time. They were also said to sometimes burst or fizzle, but this too was described while Katniss was hallucinating so it's unknown to be true. The stings themselves are extremely painful, and remain so for days unless treated. If you are stung many times in a short period of time, you can die from excess poison.
Tracker jacker venom was specifically engineered to target the part of the brain that generates fear, creating terrifying hallucinations that can drive a person to madness and within time death. The images are bizarre and seem false afterwards, though they are vivid at the time. Peeta Mellark, who received countless doses of venom, described the influenced memories as "shiny." Katniss Everdeen reported seeing a butterfly the size of a house, humming orange bubbles, and trees transforming to blood, in addition to visions of her loved ones and herself dying in horrific ways. However, the hallucinations are not purely visual. They cause the victim to feel pain and other sensations that make the experiences realistic to the point that Katniss believed they were real despite being well aware of the poison's effects. Just before Katniss blacks out, she sees ants boring into her eyes. In the film, during the hallucinations, Katniss saw Caesar Flickerman step out from behind a tree, telling the audience about the effects of the tracker jacker venom. The hallucinations lasted two days for Katniss, who received three stings. And Rue treats her stings while she's asleep
The barbed stinger should be dug out as soon as possible, which will minimize pain and accelerate healing. The crushed or chewed leaves of a particular plant can be placed on the stings to draw out the poison.
In the 74th Hunger Games, Rue uses them to treat the stings on Katniss. Rue applies them by chewing them, then applying them to the stings. Katniss also applies the leaves to Peeta's leg wound caused by Cato.Smoke can be used to sedate the tracker jackers and minimize the risk of being stung in the first place. This technique was used extensively by rebels when the wasps functioned as weapons.
Tracker jacker venom can also be used to "hijack" memories in a form of torture. A memory is called up by some sort of stimulus and tracker jacker venom is injected, in small enough quantities that it causes little physical reaction and minimal hallucination. The memory then becomes subconsciously associated with fear and pain, as well as being perceptibly warped. Afterwards, the brain rerecords the memory in the altered form, creating an effect which can never fully be healed. Little is known about its cure, although doctors from District 13 attempt to cure Peeta (who was hijacked by The Capitol) by hijacking him back (through calling up the memory and associating it with positive emotions).