When smoke gets in your eyes!

The perception that honeybees can escape an approaching wild fire by absconding in advance of the fire is so well entrenched that no thought appears to have been given to see that it is an utter fallacy. Entire apiaries in the Western Cape have been utterly consumed by fire on a fairly regular basis over the years with not a single swarm issuing from them as the fire bears down on the apiary.

The reason for such thinking is as a result of the well-known behaviour of bees to imbibe honey when a reproductive swarm departs the hive or the colony absconds. This honey stored in the bodies of workers tides the bees over the period in which they found a new colony by creating combs in which to rear brood.  Thus the reasoning that follows is that in responding to smoke by imbibing honey the honeybees are preparing to abscond.

However, a gravid queen is too heavy to fly and honeybees rarely abscond if brood is present. Thus for a swarm to issue from a hive takes preparation in advance – which is impossible with the sudden arrival of a fire. Pheromones are crucial in co-ordinating such a swarm and smoke disrupts and smothers such chemical communication – which in the case of a beekeeper using a smoker, disrupts the alarm pheromone which targets concentrated attack on the perpetrator who is disrupting the hive.

Reaction of wild colonies of honeybees to fire

Such questions regarding the behaviour of honeybees to fire were raised after the devastating wild fire in the Cape Point section of Table Mountain National Park on 4 March 2015 which incinerated 988 ha of fynbos before it was brought under control. How many of the wild honeybee swarms in this burnt area had survived the fire? We realized then that the swiftness of the fire alone would have ensured that no colony could have escaped in advance of the fire. The question then arose as to why the bees always respond to fire by imbibing honey when there is no intention to abscond? An analysis of the 17 nests within the fire zone supplied an explanation.

The fynbos vegetation is adapted to fire which is essential for its maintenance and which occurs at intervals of 15 to 25 years. Analysis of the wild honeybee nests throughout Cape Point revealed that 78% were located under rock outcrops, within clefts in rocks or in cliff faces; 11% were directly in the ground; 8% in cavities in trees and 3%within the intertwined branches of bushes. Of these nests, 68% had their openings entirely enclosed in propolis with small openings within this propolis wall serving as entrances to the nest.

Honeybee colonies within the burnt area

Within the burnt area were 17 wild nests of which 13 were situated under the bases of boulders and 4 in clefts within boulders. Propolis walls enclosed all these nests, of which two walls and adjacent combs had been totally destroyed by the fire and two walls partially destroyed. However, all these colonies survived the fire. The response of the bees to fire was to imbibe honey and retreat to the deepest recess of the cavity.

Fynbos fires are not exceptionally intense but flames tend to be high (2 to 5m) and of short duration where temperatures may reach 550 °C for only 10 seconds. Experimental fires in the fynbos spread at a rate of 0.04 t0 0.89msˉ¹. Once the fire has passed, the landscape is filled with powdery grey sand and the blackened skeletons of the larger shrubs. It is this devastation of their environment which the bees encounter after the fire has passed where neither nectar nor pollen is available to them. This is when the imbibed honey is essential to tide them over this dearth period which is about 2 to 3 weeks long before the fire-loving ephemerals sprout from underground bulbs or rhizomes and flower in profusion, having been relieved of competition from other plants. However, the surviving swarms were considerably weakened because of the suspension of foraging which was possibly followed by the eating of existing eggs and larvae which could not be reared further due to such a lack of food.

Firmly established, innate behaviour

The response of honeybees to smoke by imbibing honey which tends to make them less inclined to sting, coupled with the masking of their alarm pheromone is a godsend to beekeepers in their manipulation of hives in extensive apiaries. This behaviour is innate and firmly established. That all honeybees of the genus Apis respond in a similar way by imbibing honey in the presence of smoke indicates an evolution in a fire-prone ecology.

Original publication

Tribe, G., Tautz, J., Sternberg, K. and Cullinan, J. 2017. Firewalls in bee nests – survival value of propolis walls of wild Cape honeybee (Apis mellifera capensis). Sci. Nat. 104:29.

DOI 10.1007/s00114-017-1449-5

http://rdcu.be/p2u4

HOBOS

Acknowledgment: The permission granted by SANParks to locate and analyse the nesting sites of honeybees in the Table Mountain National Park is gratefully acknowledged.

The authors at work…

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