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 land mines 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 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 were used by the Capitol to keep people out of restricted areas in the districts.
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 stung many times in a short period of time, victims can die from excess poison.
Tracker jacker venom was 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. It is noted that the hallucinations have also caused victims to be unable to distinguish between actual or imaginative events.
In the 74th Hunger Games, Rue uses a special type of leaves 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 SedationSmoke can be used to sedate 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. Real vespids are also affected by smoke, and it shows that muttations still retain some original factors of the animals they were based on.
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).
In the books, Glimmer was killed by tracker jackers after she began running, but tripped over the tree branch. The girl from District 4 was badly stung too, so she ran to the lake, but died along the way.
In the film, Glimmer died at the bottom of the tree. The girl from District 4 did not die as she died at the bloodbath. When Katniss was cutting the nest to land on the Careers she was stung several times. Peeta Mellark was also a victim of the tracker jackers along with some of the Careers.