- Bees of the genus Lisotrigona were recorded feeding on human sweat and tears in two instances in Mizoram and Chhattisgarh. The feeding of insects on tears and sweat is called lachryphagy and sudophagy, respectively.
- This activity by bees is common in Thailand and there is also a report from Sri Lanka. Bees collect sweat and tears like nectar.
- While all the bees studied, in this case, are females, further studies are being made to collect male bees for identification of the species, to understand their feeding behaviour, foraging activity in different seasons, the chemical composition of sweat and tear, nest structure, and their distribution.
A team of researchers studying stingless bees have observed that the bees feed on the sweat and tears of humans – reportedly, a first-of-its-kind finding from India. The reports of the sweat and tear-feeding bees were from Mizoram and Chattisgarh.
“All these stingless bees belong to a genus known as Lisotrigona. They are quite small – three mm or less in length. These bees are rare and occur in Kerala, Maharashtra, Madhya Pradesh, Chhattisgarh and Mizoram. They collect a small quantity of honey which is of golden yellow colour and very sweet,” Shashidhar Viraktamath, co-author of the study and Emeritus Scientist, Biosystematics Laboratory, Department of Entomology at the University of Agricultural Sciences, Bengaluru, told Mongabay-India.
“We found these bees drinking human sweat and tears for the first time in India. But they are common in Thailand and there is also a report from Sri Lanka. Just like nectar, these bees collect sweat and tears and may store them in their nest and utilise them whenever required. The sweat and tears are a source of protein and salt for these bees. Ancestors of bees were carnivores. But during the course of evolution the honey bees developed feeding on nectar and pollen,” he said. This specific study was done only on female bees this time.
The feeding of insects on tears and sweat are called lachryphagy and sudophagy, respectively.
Hans Bänziger of Department of Entomology and Plant Pathology at Chiang Mai University, Thailand, who has published an account with photographic documentation of lachryphagy by bees, reported that one — and probably the main — compound these tears-consuming bees seek are proteins. In a 2018 study, he showed (by markings) that the same specimen of Lisotrigona furva and Lisotrogona cacciae repeatedly flew between his eyes and their nest to collect and deliver tears, dozens of times for many hours, even days. They would do so even after rain or during a light drizzle, so they were not seeking water, at least in such cases, and salt is not required in such amounts. On the other hand, proteins are scarce, not easy to obtain and hence the most valuable resource, essential for the bees’ rearing of their young. Honey bees and most other bees obtain proteins from the pollen they collect, which Lisotrigona also does to some extent.
Viraktamath says the study hypothesises that this behaviour may represent a transition status from carnivory to highly specialised feeding behaviour of nectarivore (nectar-feeding) and palynivore (pollen-feeding). “It will be interesting to study the detailed chemical composition of the tears and sweat and to find out whether any other chemical acts as an attractant to these bees besides meeting the needs of sodium and proteins.”
Twenty-eight lachryphagous and sudophagous bees collected from three locations – one in Mizoram and two in Chhattisgarh – as part of the present study, are females. “Further studies are being made to collect male bees for identification of the species, to understand their feeding behaviour, foraging activity in different seasons, the chemical composition of sweat and tear, nest structure, and their distribution,” he said.
Small and rare stingless bees
Stingless bees of the genus Lisotrigona are rare and only four species namely, L. cacciae (Nurse), L. mohandasi Jobiraj and Narendran, L. revanai Viraktamath and Sajan Jose and L. chandrai Viraktamath and Sajan Jose, are known from India.
Viraktamath conducted a study on the diversity of stingless bees in 2017. “When I started I learnt that there are so many misidentifications of the species as most of the researchers used only females to identify. However, females of different species are remarkably similar and it is very difficult to identify. No one tried to collect male bees and study them. Hence, before the COVID-19 pandemic started, I travelled throughout India and collected both female and associated male bees. Male bees have strong diagnostic features because of which we can identify the species without ambiguity. Luckily my students joined me and we started collaborative studies to understand the diversity of Indian stingless bees. During this endeavour, we came across these bees feeding on sweat and tears,” he said.
Two researchers in the team, Rojeet Thangjam and Shubham Rao, volunteered to allow the bees to feed their sweat and tears to study their foraging behaviour for about a week.
Lisotrigona bees, which are black or dark reddish-brown in colour, were observed collecting nectar and pollen from rapeseed flowers in Mizoram. First author Thangjam, Assistant Professor (Entomology) at the Central Agricultural University Thenzawl, Mizoram, started collecting specimens and sending them to Viraktamath for confirmation, who found them to be Lisotrigona sp.
Narrating his experience as a volunteer to observe the feeding of the bees, Thangjam said, “One day I was sitting on the verandah after my breakfast, and a few bees (around 2-3) started hovering around my head (near ears and eyes). I was disturbed and annoyed by these bees so I caught one of them with my hand and noticed that it was the stingless bees that I had collected earlier. So I decided to see why they are hovering around my ears and eyes. At first, these tiny bees used to hover around the head, ears and eyes during daytime when our body started sweating around 9:00 am till the evening hours of 3-3:30 pm.”
“One worker bee flew or hovered first around the head, ears and face and after a few minutes, 3-4 bees started hovering and were trying to taste the sweat near the forehead and ears. After hovering for around 7-8 minutes, they tried to enter the eyes. However, due to continuous blinking of the eyes, they hesitated to sit on my eyelids and drank the tears. After attempting for a few minutes, they approached the eyelashes and drank the tears by sitting on the eyelashes. They sucked the tears for about 45-50 seconds even after the eyelashes blinked and then they flew away. Around 2-3 bees drank tears simultaneously from both eyes. They used to come back to collecting tears just like collecting nectar from flowers. I observed that the bees that had already drunk tears used to come directly to my eyes, but those who are new used to hover around my head for some time,” explained Thangjam.
In Chhattisgarh, similar behaviour was observed in two locations, narrates Shubham Rao of Department of Entomology, Indira Gandhi Krishi Vishwavidyalaya, Raipur and co-author of the study. Rao also volunteered to have the bees feed on his sweat and tears. While travelling from Pakhunjur to Raipur on a two-wheeler, Rao stopped at Bhanupratappur to take a rest. He took out the helmet as his head and face were covered by sweat. Within 4-5 minutes, five bees started hovering around the nose, eyes, forehead, ears, and sweaty hands. After a couple of minutes, two bees alighted on the fingers and one on the nose and started drinking sweat. Two bees alighted near the eye, slowly crawled to the lower eyelid, and drank the tears. The feeding lasted for 120-180 seconds and then the bees flew away. The second incident occurred at the forest guest house of Barnawapara wildlife sanctuary in Chhattisgarh, where feeding by the bees lasted for 60-120 seconds and went on for a couple of hours with intermittent breaks.
Samples of the bees were identified as three species of Lisotrigona and then photographed at the Department of Entomology, University of Agricultural Sciences, GKVK, Bengaluru.
Sajan Jose, who has worked on stingless bees in Kerala and who is not associated with the study told Mongabay-India, “Stingless bees take sweat from the human body. I [have also] observed it. It is a common phenomenon in Kerala. Dr. Viraktamath published it first. They take sweat for their mineral requirements. Tears also contain salt. So, there is every possibility that stingless bees take tears also,” he said.
Banner image: Lisotrigona bee hovering around eyes. Photo by Rojeet Thangjam.