That’s a picture of Paraponera clavata, or a bullet ant. It can grow to be about an inch long.
They’re among the world’s most venomous insects, and are supposed to deliver the most painful sting of any insect, according to J.O. Schmidt. He’s an entomologist who’s been stung by pretty much every hymenopteran possible and who developed a pain scale rating that lists the relative pain caused by insects. His ratings go from 0, where the sting is as mild as the little zap you might feel while walking across a carpet in your socks, up to 4, where you might as well just lie down and scream. Bullet ants get a 4+. When he later revised his index, he described bullet ant stings as “pure, intense, brilliant pain, like walking over flaming charcoal with a three-inch nail in your heel.”
But wait, it gets worse.
The ants have abdominal stridulatory organs—that means they can shriek at you when threatened, which alerts the rest of the group to come boiling up out of the nest to help impale you.
There’s a tribe of people in Brazil, deep in the Amazon forest, the Satere-Mawe, who use bullet ants as an initiation rite to manhood. Boys have to slip on gloves that resemble oven mitts, and which are teeming with bullet ants. They have to keep the gloves on for ten minutes. Evidently paralysis of the arms sets in rather quickly, so it’s after the gloves come off that the real pain and convulsions begin—and they last at least 24 hours.
Did I mention these ants also shriek?
Here’s another picture for you:
Schmidt, Justin O. (1990). "Hymenoptera Venoms: Striving Toward the Ultimate Defense Against Vertebrates". In D. L. Evans and J. O. Schmidt. Insect Defenses: Adaptive Mechanisms and Strategies of Prey and Predators (Albany, New York: State University of New York Press). pp. 387–419
http://blog.nus.edu.sg/lsm1303student2013/2013/04/11/biting-the-bullet-defense-mechanisms-of-bullet-ants-paraponera-clavata/