This past summer, you and I probably shared a similar bee experience: outside on a hot day, little metallic bees stuck to your bare arm, lapping up sweat from your skin.
These bees, called sweat bees, are from the Halictidae family and are very common. Between the US and Canada, there are approximately 520 known species of these shiny, and often colorful (like this Agapostemon texanus), insects. But why do they drink sweat?
Salt is necessary for egg production in insects (a female butterfly can lose more than 50% of the salt she’s born with in just one egg complement) and human sweat is absolutely loaded with it. Many insects have a hard time meeting their salt requirements, since nectar and pollen are not high in salts. This leads insects to drink our sweat, or even tears (a behavior exhibited by some bees from the Apidae family, though they may be after proteins too). Bees, moths, and butterflies will alight on the eyes of crocodiles and drink from mud puddles, feces, and urine to meet their salt needs.
In butterflies, this ‘puddling’ behavior (named for the plethora of butterflies found at mud puddles) is mostly seen in males, who transfer huge amounts of salt to females in their sperm. However female bees are commonly found drinking human sweat (which is why you may have experienced an unpleasant pinch when you try to brush one off your skin). This behavior is not believed to be harmful, so next time you see a sweat bee tell her: ‘Drink up!’
Sources and Further Reading:
Adler P, Pearson D (1982). Why do male butterflies visit mud puddles? Canadian Journal of Zoology, 60: 322-5.
Banziger H, Boongird S, Sukumalanand P, Banziger S (2009). Bees (Hymenoptera: Apidae) That Drink Human Tears. Journal of the Kansas Entomological Society, 82: 135-50.
Barrows, E (1974). Aggregation Behavior and Response to Sodium Chloride in Females of a Solitary Bee, Augochlora pura (Hymenoptera: Halictidae). The Florida Entomologist, 57: 189-93.
Dangles O, Casas J (2012). The bee and the turtle: a fable from Yasuni National Park. Frontiers in Ecology and the Environment, 10: 466-7.
Pivnick K, McNeil J (1987). Puddling in butterflies: sodium affects reproductive success in Thymelicus lineola. Physiological Entomology, 12: 461-72.