How
bees stay cool on hot summer days
BY LEAH
BURROWS
If you’ve ever walked past a bee’s
nest on a hot summer day, you’ve probably been too focused avoiding getting
stung, rather than stopping to wonder how all those bees stay cool. Don’t worry, Harvard scientists have braved the stingers to ask and answer that question for you.
Honey bees live in large, congested
nest cavities, often in tree hollows with narrow openings.
When it gets hot inside the nest, a group of bees crawl to the entrance and use their wings as fans to draw hot air out and allow cooler air to move in.
The question is, how do bees self-organize into these living ventilating units?
When it gets hot inside the nest, a group of bees crawl to the entrance and use their wings as fans to draw hot air out and allow cooler air to move in.
The question is, how do bees self-organize into these living ventilating units?
Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Department of Organismic and Evolutionary Biology (OEB) have developed a framework that explains how bees use environmental signals to collectively cluster and continuously ventilate the hive.
“Over millennia, social insects such
as bees have evolved to harness and exploit flows and forces and collectively
solve physiological problems such as mechanical stabilization, thermoregulation
and ventilation on scales much larger than the individual,” said L Mahadevan, de Valpine
Professor of Applied Mathematics, Physics, and Organismic and Evolutionary
Biology, and senior author of the study.
“A combination of measurements and computational models quantify and explain how fanning bees create an emergent large-scale flow pattern to ventilate their nests.”
“A combination of measurements and computational models quantify and explain how fanning bees create an emergent large-scale flow pattern to ventilate their nests.”
“We have demonstrated that bees
don’t need a sophisticated recruitment or communications scheme to keep their
nests cool,” said Jacob Peters, a postdoctoral fellow in SEAS and OEB, and
first author of the paper.
“Instead the fanning response of individual bees to temperature variations, and the physics of fluid flow leads to their collective spatial organization, which happens to lead to an efficient cooling solution.”
“Instead the fanning response of individual bees to temperature variations, and the physics of fluid flow leads to their collective spatial organization, which happens to lead to an efficient cooling solution.”
Experiments began in the dog days of
the summer of 2017. Over the course of several weeks, Peters, Mahadevan and
former postdoctoral fellow at SEAS Orit Peleg monitored a group of man-made
beehives in Harvard University’s Concord Field Station.
The research team measured
temperature, air flow into and out of the nest, and the position and density of
bees fanning at the nest entrance.
They observed that rather than spreading out across the entirety of the nest entrance, the bees clustered at the hottest areas and kept those areas, which had the highest air outflow, separate from the cooler areas with the highest air inflow.
Importantly, they found that different bees had different temperature thresholds above which they would begin fanning, so that collectively they were better at responding to temperature variations.
They observed that rather than spreading out across the entirety of the nest entrance, the bees clustered at the hottest areas and kept those areas, which had the highest air outflow, separate from the cooler areas with the highest air inflow.
Importantly, they found that different bees had different temperature thresholds above which they would begin fanning, so that collectively they were better at responding to temperature variations.
In modeling the system, the
researchers found that all these behaviors linked to the environmental physics
of the nest.
Fanning outward allows the bees to sense the upstream nest temperature; different thresholds of temperature allows for more continuous ventilation and more stable hive temperatures; and, because of the physics of friction and flow, clustering to separate inflow from outflow allows more cool air to enter the nest because of the physics of friction and flow.
Fanning outward allows the bees to sense the upstream nest temperature; different thresholds of temperature allows for more continuous ventilation and more stable hive temperatures; and, because of the physics of friction and flow, clustering to separate inflow from outflow allows more cool air to enter the nest because of the physics of friction and flow.
“Our study demonstrates how
harnessing the dynamics of the physical environment allows for large-scale
organization of a physiological process,” said Peleg, who co-authored the paper
and is now an Assistant Professor at the University of Colorado Boulder.
“Although this is a physics-focused
story, biological variation with roots in genetics and evolution likely plays a
big role in order for this system to work,” said Peters.
“Our theory suggests that not only does individual variability in temperature threshold lead to a more stable hive temperature but also this diversity is critical to the stability of the patterning of fanning behavior which is required for efficient ventilation.”
“Our theory suggests that not only does individual variability in temperature threshold lead to a more stable hive temperature but also this diversity is critical to the stability of the patterning of fanning behavior which is required for efficient ventilation.”
“In everything from large HVAC
systems to the fans that cool our computers, bioinspired, self-organizing
systems may be able to adapt and respond to specific demands better than
current systems,” said Peters.
“More broadly, our study highlights,
yet again, the need to consider both biological organisms and their physical
environments to understand the richness of collective eco-physiology, a
hallmark of life itself,” said Mahadevan.
This work was supported by the
National Science Foundation.