Weird Science | Understanding the science behind “killer” bee attacks

On April 7, a group of 50 residents of Sitapur village in Rae Bareli district in Uttar Pradesh, gathered in the shade of trees for a condolence meeting after the death of a monkey in the village. Within minutes, the sombre setting turned chaotic, when they were attacked by a swarm of bees. A few were grievously injured, and 65-year-old Rati Pal fell unconscious. By the time the villagers rushed him to the nearby hospital, he had died. His body has been sent for post-mortem to learn the exact cause of death. A month ago, in Tisa Khanapur village in the same district, an elderly woman and her husband were attacked by bees after someone broke a hive in their field; the woman, Govinda, who too was in her mid-60s, died after being stung.

For the most part, bees are innocuous winged insects that perform the vital role of pollination and thus ensure food security and ecological balance for the rest of us. Their stings hurt, but they don’t usually cause deaths.

So what happened in Rae Bareli?

Different types of bees

For a bee sting to fatally affect a person, the person must be allergic to the bee’s venom and they should have been attacked by many (a swarm).

Except for stingless bees, all bees can sting, according to entomologist Vasuki Belavadi, but most don’t. It is the social bees, the ones that live in a colony that are more likely to do so. Interestingly, less than 10% of the 20,000 extant species of bees are social, and these include bumble bees, honey bees, and stingless bees.

Experts say that bee attack cases such as the recent ones in Uttar Pradesh are likely carried out by Apis dorsata, more commonly known as the giant honeybee or rock bee. This is one of the 12-odd known species of honeybees and one that we are most familiar with, as they build hives on buildings and trees. They are social bees and live in colonies that they are hard-wired to protect. Belavadi, a retired professor of the University of Agricultural Sciences in Bengaluru, said that rock bees tend to always be on guard because, unlike other honeybee species, their nests are open and vulnerable to attack, not just by humans who see them as a nuisance, but also by birds and other animals who prey on them.

“They are known to be easily agitated and that makes them dangerous,” Belavadi said. “If a swarm of bees has attacked someone, there must be a nearby colony that was intentionally or unintentionally disturbed,” he added.

The term “killer bee” usually refers to the Africanised honey bee, a subspecies of Apis mellifera. In 1956, Brazil imported African honeybees intending to cross-breed them with local bees and boost the country’s honey production. However, in 1957, a year after this experiment, some of the bees escaped from the apiary, and crossed with other subspecies, resulting in a super-aggressive subspecies that spread all the way to the US. These bees caused significant damage to life and agriculture and even inspired a Hollywood film The Swarm (1978). Africanised honey bees are only found in South America and North America.

But terms like killer bees give the wrong idea about bees. It may be useful to remember that just as stinging a human is self-sabotaging for a honey bee, indiscriminately eliminating beehives does the same for human beings.

What does the venom have?

The act of stinging is not something a honeybee enjoys; in fact, it is suicidal for it to do so. Once they sting a hard-skinned mammal, the sting remains embedded in the victim. The honeybee cannot survive this. Only if they detect that their colony is in danger, would they inflict this upon themselves.

When a honeybee stings a human, it leaves behind chemicals called alarm pheromones that act as a cue for its colony mates to join the battle against the perceived threat. According to one study published in the journal Insects in 2019, beekeepers interpret the pheromones’ banana-like smell as a sign that their bees are stressed.

Injuries and deaths due to venomous animals have always been a concern for human beings, but much more so now with urbanisation and loss of natural habitat exacerbating the human-wildlife conflict. For these reasons, the composition and working of venom is a subject of great interest among venomics researchers and immunologists.

Mihir Kumar, a PhD scholar at the Evolutionary Venomics Lab at the Indian Institute of Science (IISc), Bengaluru, pointed out that honeybee venom is relatively “simple” in comparison to the complex proteins that constitute snake and other animal venom. It is primarily composed of a peptide molecule called melittin, phospholipase A2, other enzymes and low-weight proteins.

For most people, the sting is likely to result in some local inflammation, but the venom is capable of wreaking havoc in a person, but only if they are allergic to the venom. “Hypersensitive people can die of heart failure,” said Dipyaman Ganguly, an immunologist at the Institute of Chemical Biology, Kolkata.

That’s because such people are likely to have a higher supply of an antibody called Immunoglobulin E (IgE). The IgE molecules recognise the entry of the toxins in the honeybee venom and this triggers a further increase in production of IgE. This, in turn, prompts immune cells known as mast cells and basophils to produce chemicals called histamines, which are characteristic of allergic reactions. In the worst case, this chain of events can lead to immune cells breaching the walls of blood vessels, leading to more pressure being needed to pump blood to the heart. The result could be fatal.

A general idea of the working of the human immune system shows why one person’s reaction to bee stings is drastically different from another’s. Based on symptoms, appropriate medical interventions can be taken, like administration of antihistamines.

Nandita Jayaraj is the co-author of Lab Hopping: A Journey to Find India’s Women in Science, which explores the gender gap in Indian science.