How bees survive a heat wave

Thoroughly delightful little creatures having an awfully hard time…

In some parts, October is known as ‘suicide month’. It’s about the constantly rising temperatures, the lack of rains, the winds, the white heat, and the dust. So much dust. Slowly, day after day, the clouds start appearing, – then disappearing again… Like an ephemeral promise that nature is unable to fulfil. Just when you think you cannot bear it anymore, the heat goes up another notch. Until one morning feels different. The air is cooler when you wake, the dawn is pink with the sun reflecting off scattered clouds and the real promise of rain hangs in the air like a promise of sweet relief. Today feels like that – like the summer rains are imminent. The birds chirp enthusiastically, and in the distance I hear the call of the “Piet-my-Vrou” – the red-chested cuckoo. A little closer I hear the liquid rising and falling call of the Burchell’s coucal – let’s hope the Rainbird lives up to the legend and is indeed heralding the rain.

During these trying times, my heart always goes out to the birds, insects and animals. Whilst we are actively able to assist our domestic pets, what happens to the wildlife? More specifically, what happens to bees began to intrigue me. The World Meteorological Organization defines a heat wave as “five or more consecutive days during which the daily maximum temperature surpasses the average maximum temperature by 5 °C or more”. Jozi’s heat began in early October, and only now, more than two weeks later, do the rains and lower temperatures appear to be on the horizon. If you consider that the average life span of worker honeybee ranges from five to seven weeks, two weeks of heatwave is a hugely significant portion of their lives.

Regardless of the ambient temperature, the in-hive microclimate of a beehive at the central brood area must be kept at the average optimum temperature of 32 °C–36 °C for the colony to survive. For millions of years, honeybees evolved to live in tree hollows, which are perfectly insulated with the surrounding wood. That said, with the decimation of forests, that is no longer an option – and modern hives don’t have the same insulating properties. So, what happens when ambient temperatures are very high? During the days, overheating due to overcrowding is unlikely as most worker bees are out foraging and drones are also outside the colony. At night, if the hive is overcrowded, the bees instinctively hang outside in front of their hive’s entrance, spending the night outside and staying cool. Those are the basics of thermoregulation.

A close-up image of a magical insect.

There are, however, several other cooling strategies which can be employed by the worker bees in the beehive. Bees are able to ventilate the hive by actively fanning their wings. In one study (Southwick and Moritz, 1987), when the air temperature inside the brood nest was approaching 35 °C, several hundred bees positioned themselves throughout the beehive (i.e. left, right, top and bottom) to take up the fanning position in the ventilation process. These bees, called ‘fanners’, force air circulation throughout the beehive. As temperatures increased to around 40 °C, 20–30 bees relocated to the entrance (onto the screened landing platform) and began fanning. They also used a ventilation strategy by organising themselves into groups and separating regions of continuous inflow and outflow at the hive’s entrance. During this air exchange, the gaseous exchange of oxygen and CO2 and control of humidity will also be taking place. 

Bees returning to a man-made hive.

A second strategy used by honey bees to protect their broods is a technique known as “heat shielding”. The worker bees absorb heat by pressing the ventral side of their bodies against the heated surface, later flying to area in the hive that is cooler than the brood area, thereby dissipating the absorbed or stored heat.  (Ref: Bonoan et al., 2014).

Evaporative cooling is also utilised. Worker bees spew water that they’ve carried to the beehives in their bodies, whilst other worker bees will then begin fanning. This actively creates cool, humid air which circulates throughout the hive. Bees instinctively know that cool air drops, and therefore the water is normally dispersed from the top of the hive, under the lid.

Another issue is the negative effect of heat on sperm. Young honeybee queens have only one brief mating period early in life, and then they store the sperm they acquire for the rest of their lives (up to 5 years). As the ONLY egg-layer, the colony’s productivity directly depends on the queen’s reproductive output, which in turn depends on the viability and abundance of her stored sperm. High temperatures significantly reduce the sperm’s viability.  

Gossamer wings reflect the sunlight.

Much like the airplanes trying to take off from the Maun airport in summer, a bee’s ability to fly begins to be compromised at around 37°C. A bee dies when its body temperature reaches 41°C. High temperatures and a lack of water also cause flowers to die – reducing the bees’ food supply even further. But what can we do to help bees during these trying times?

You can assist them by providing water – ideally in shallow trays with pebbles/marbles/corks (which keep worker bees from drowning in the water when they come for a sip) in the bowl can be placed outdoors / in the garden to support honey bees in a heat wave. 

A Facebook post claiming to be from Sir David Attenborough urging people to leave sugar water out for struggling and tired bees has been outed as a fake. In fact, it is positively harmful to bees. Whilst a teaspoon of sugar can assist in reviving a single collapsed bee, readily available sugar water is, in effect, the equivalent of mass feeding them junk food. It’s full of carbohydrates which will obviously give them an energy burst but has no other nutritional value! It will not feed the growing larvae when it is taken back to the hive. As the sugar water is easier to access, they will flock to the solution rather than forage for nectar – which will be disastrous for the hive and the environment. Rather plant nectar-rich, ideally indigenous plants in your garden – they will be able to withstand the drought and the heat, look beautiful and feed the bees when everything else is fading fast. 

Jacqui Ikin & The Cross Country Team