Venoms and Stings: From Fear to Fascination

A fire ant (Solenopsis sp.) waves a drop of venom from its stinger [1]

There are two species of ants in the lab: turtle ants (Cephalotes varians) and elongate twig ants (Pseudomyrmex gracilis). I want to say that I love them equally, but I don’t. Turtle ants are small, chubby, and essentially harmless. I’ve heard them (accurately) described as the puppies of the ant world. Twig ants, on the other hand, are long, skinny, and have stings that are more painful than a hornet’s. Every time I have to feed the twig ant colonies, my senses are heightened, my heart pounds in my chest, and my hands are poised to shut the colony box at any moment. Everyone in the lab is afraid of the twig ants, albeit some more than others, but thankfully none of us have been stung yet. Although I can’t say that I am particularly fond of twig ants, I have to admit I am impressed that such tiny creatures can have such a powerful effect on us. I decided to tackle my fear head-on by replacing it with scientific fascination, so I set out to understand the science behind ant stings and venoms.

As it turns out, 71% of all known ant species can either sting or spray secretions from their venom glands. The venom is comprised of a different mix of organic compounds for different species, but it commonly includes formic acid or alkaloids. Some species can also pack a painful punch by biting with their mandibles instead of stinging or using venom. Despite the prevalence of ants and the widespread study of ants in general, their venoms have been largely unstudied. This is partly due to their small size and low venom yield, but also due to the misconception that their venoms are relatively “primitive” by being comprised of mostly formic acid. Research on ant venom and stings have been increasing; here, I will focus on a few species that have been more well-studied.

One of the most prevalent species of stinging ants is the fire ant (genus Solenopsis). Fire ants use their venom to stun their prey and swarms of these ants are able to overcome large animals. They first bite their victim with their mandibles to anchor themselves, then they inject their venom through stingers from their gasters (or in less scientific terms, their butts). Their stingers and venom sacs are connected to their Dufour’s gland, which can release pheromones to recruit even more ants to attack. Fire ants can also spray their venom through a behavior called gaster flagging. When they are confronted with threats like colonies of other ant species, they raise their stingers in the air and shake their gasters rapidly, spraying venom everywhere.

Anatomy of the stinger for a fire ant [2]

Unlike honeybees and several other Hymenoptera species, ants can sting their victims multiple times, until they run out of venom in their venom sac. In some cases, humans can develop allergic reactions to the venom if they have been stung frequently. Rarely, this can lead to anaphylactic shock but mostly, you’ll just be left with a very itchy blister that will heal on its own in a few days. Only 0.1% of fire ant venom is made of proteins, which are responsible for the allergic reactions seen in humans. In contrast, proteins make up of 10 to 20% of honey bee venom.

The main component of fire ant venom is an alkaloid called solenopsin. While solenopsin is basic with a pH greater than 7, the venom of many other ant species is acidic with a pH less than 7. This has led to some interesting behavior in tawny crazy ants (Nylanderia fulva), a competitor species. When confronted with fire ants, tawny crazy ants secrete formic acid from their own venom glands and rub themselves with it, allowing them to neutralize the effects of the fire ant venom. Without such protection, solenopsin can promote cell lysis, causing cells to rupture once it is injected . Despite these harmful effects, scientists from Emory University have recently discovered that solenopsin can be used to treat psoriasis, an autoimmune skin disease that is currently incurable. This speaks to an increasing trend of studying venoms and their effects for biomedical applications.

Science Behind a Fire Ant's Sting [3]

The venom of other notable ant species--the bulldog ant (genus Myrmecia) and the bullet ant (Paraponera clavata)--have also been recently studied. Bulldog ants are likely the most dangerous ants that we know. They are extremely aggressive and they can deliver both a bite from their jaws and venom from their stinger. Their venom is so powerful that they have been known to kill an adult within 15 minutes. Through a comprehensive analysis on the venom, scientists from the University of Queensland have been able to pinpoint its effects on the human nervous system. They suggest that further studies can uncover how pain in general is sensed by humans and this has the potential to lead to new pain treatments.

Bullet ants are less dangerous but perhaps more notorious, likely due to their memorable name--a reference to how the pain of being stung is comparable to being shot by a bullet. In fact, they rank #1 on the Schmidt Sting Pain Index. The effects of the venom can be felt for up to 24 hours, and the main culprit responsible is a neurotoxin called poneratoxin. Poneratoxin hinders the signaling ability of nerve cells by interfering with sodium ion channels responsible for action potentials. Most of the time this leads to pain but ironically, it can also lead to the suppression of pain at low concentrations. It has been proposed as a painkiller and further research is being done to understand its potential in even more applications, such as using it develop insecticides. Thus, while the venom and stings from these ants can be frightening, there is a lot more that we can learn from them if we replace our fear with a little scientific curiosity.

The infamous bullet ant (Paraponera clavata) [4]

Further Reading
dos Santos Pinto, J. R., Fox, E. G., Saidemberg, D. M., Santos, L. D., da Silva Menegasso, A. R., Costa-Manso, E., ... & Palma, M. S. (2012). Proteomic view of the venom from the fire ant Solenopsis invicta Buren. Journal of Proteome Research, 11(9), 4643-4653.

Robinson, S. D., Mueller, A., Clayton, D., Starobova, H., Hamilton, B. R., Payne, R. J., ... & Undheim, E. A. (2018). A comprehensive portrait of the venom of the giant red bull ant, Myrmecia gulosa, reveals a hyperdiverse hymenopteran toxin gene family. Science Advances, 4(9), eaau4640.

Szolajska, E., Poznanski, J., Ferber, M. L., Michalik, J., Gout, E., Fender, P., ... & Chroboczek, J. (2004). Poneratoxin, a neurotoxin from ant venom: Structure and expression in insect cells and construction of a bio‐insecticide. European Journal of Biochemistry, 271(11), 2127-2136.

Zamith-Miranda, D., Fox, E. G., Monteiro, A. P., Gama, D., Poublan, L. E., de Araujo, A. F., ... & Diaz, B. L. (2018). The allergic response mediated by fire ant venom proteins. Scientific reports, 8(1), 14427.

Media Credits

[1] Photo by Alex Wild https://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Solenopsis

[2] Photo by Eric Keller https://www.popsci.com/fire-ants-and-how-they-sting-video

[3] Video by Eric Keller https://www.youtube.com/watch?v=u-NrZYekRcs

[4] Photo by Alex Wild https://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Paraponera