The sting of Paraponera ants, better known as Bullet ants, is exceptionally painful – and researchers have finally discovered why.
When we think of the animals with the most painful sting, we instinctively think of wasps and hornets, and rightly so. We can for example mention the Pepsis wasp, better known under the name of tarantula hawk (or “tarantula hawk”, in reference to the arthropods it hunts to lay its eggs there); this species is known to cause fairly brief, but almost excruciating pain in its victims.
But the Schmidt scale, which classifies insects and Hymenoptera according to the pain they cause, does not only list flying beasts. At level 4, the highest of this classification, we also find ants of the genus Paraponera.
It is no coincidence that the latter is nicknamed ” bullet ant “. Its sting is so painful that it is often compared to the impact of a rifle bullet, hence its name. It’s hard to objectively determine if it’s worse than Pepsis Wasps, but it’s regularly cited as the most painful sting in the animal kingdom.
In his early work, Schmidt describes a ” pure, intense, bright pain, like walking on hot coals with a 10 cm nail driven into the heel “. And this torture can last up to twelve hours in some cases. It is easy to understand why the inhabitants of the regions concerned, such as Guyana, have learned to avoid them…
Until very recently, no one had been able to determine why this venom causes such reactions for such a long time. This is largely due to the size of the ants, which makes collection very difficult. But that has finally changed. For the first time, Samuel Robinson, an Australian molecular biologist from the University of Queensland, has been able to identify the physiological mechanisms that make this venom so fearsome.
open the door to pain
His team observed that the venom doesn’t just cause a burn using acidic compounds, like that of fire ants; instead, it contains poneratoxin, a neurotoxic peptide that literally opens the floodgates of pain at the molecular level.
To understand how this venom works, you have to take a little detour to explore the mechanisms of pain. At the base, there is a set of specialized cells – the nociceptors – connected to nerve endings. Once stimulated beyond a certain threshold, they emit a signal to the central nervous system. This message travels through the spine to the brain, where it will be directly translated into a more or less unpleasant sensation.
At the end of these sensory neurons are what are called sodium channels. Without going into detail, they are actors in an exceptionally important signaling mechanism that plays a central role at all levels of our physiology. Very vulgarly, these canals work a bit like toll tunnels; they open and close in response to certain stimuli to let through or block sodium ions (Na+).
This generally results in the stimulation of certain nerve cells… such as the nociceptors mentioned above. Under normal conditions, the sodium channels found in sensory cells open very briefly. But the situation changes radically when we integrate this famous poneratoxin into the equation.
A one-of-a-kind venom
By testing this substance on mouse cells grown in the laboratory, the researchers observed that it is capable of binding to sodium channels. This has the effect of facilitating their opening. This leads to the stimulation of associated sensory cells, which results in intense pain. But the poneratoxin does not stop there; it also forces the channels to stay open for an excessively long time. At the end of the chain, this results in a deluge of neurotransmitters that generates intense and nagging pain.
A fairly rare mechanism in the animal world according to the authors of the study. Certainly, there are very many compounds that can alter the functioning of sodium channels. But so far, researchers haven’t found any others that work on the same model.” These neurotoxins that target sodium channels are exclusive to ants, no one has ever found anything that looks or works the same says Robinson.
A research avenue for pain management
This work may be able to help design remedies to relieve these very painful bites. But this is not the team’s priority objective; the authors of the study are working on a larger scale. Robinson and his colleagues are primarily concerned with understanding the mechanisms of pain, and work like this is perfect for identifying all the nuances. “We want to understand pain at the molecular level and these toxins are fantastic tools to do that,” he says.
This study will not revolutionize medicine on its own; but it is in this field that it presents a real interest. By learning to control the mechanisms of pain, we are also getting closer to new methods that will relieve it.
Eventually, work of this kind could serve as a basis for developing new treatments for acute or chronic pain, whether medicinal or based on alternative approaches such as brain-machine interfaces such as Neuralink. They could also advance the management of certain neurological diseases such as epilepsy, which is closely linked to the activity of sodium channels. And all thanks to a big ant that often does more harm than good to humans who cross its path.
