Naturalist on the Bibbulmun - the Banksia Bee mating season

12 April 2023

Djeran is marked by the arrival of a cooling breeze from the southwest, night temperatures begin to fall and the morning air, heavy with petrichor foreshadows the coming rains of Makuru that will restore life to our parched bushlands, and walkers to the Bibbulmun Track.

The flowering of the firewood banksia (Bulgalla) heralds the onset of Djeran. Heavily laden with nectar (mangite), these flowers were soaked in water to provide a sweet drink. Banksia nectar is valued by many of our native birds and mammals, including bandiny (New Holland honeyeaters), ngoolyak (Carnaby’s black cockatoo) and noolbenger (Honey possums). Perhaps fewer will know of the importance of Banksia for our native bees.

 

Banksia bees (Hylaeus alcyoneus) rely exclusively on the pollen and nectar of banksia for their reproduction, and a banksia spike with newly opening flowers will become the source of considerable acrimony for male banksia bees. Unlike introduced honeybees, our native banksia bees are solitary. The females nest within holes or crevices in dead branches, either on the banksia itself or on a nearby fallen tree, and they will visit banksia flowers to collect pollen and nectar with which to provision their young.

The males will defend a nectar rich flower spike in order to control access to the visiting females in the hope of mating with them.  A male will not tolerate the presence of other males, and will grapple with and bite any rival that tries to visit or usurp his flower spike.  Males will defend the same flower, sometimes for days, until such time as its nectar rewards decline and the females move on to a new flower spike. The largest males are better able to defend flowers and obtain the most matings, a process, recognized by Charles Darwin as sexual selection, that has led to reversed sexual size dimorphism. For typically female bees are larger than male bees, but the reverse is true for banksia bees. 

Rather than forgo the opportunity to mate, the smaller males will adopt an alternative mate-searching tactic. Although unable to defend their own flower spike, they patrol many flower spikes in the hope of meeting and mating with a female outside of the territories of the larger males.  Banksia are magnets also for introduced honeybees, indeed honeybees outcompete our native banksia bees and reduce their ability to produce offspring.  But look closely next time you pass a banksia, particularly on the southern coastal heaths, and you might be lucky to find them.

Leigh W. Simmons

Leigh is the author of the fascinating book Naturalist on the Bibbulmun.  His book is available from our shop and all royalties are generously donated to the Bibbulmun Track.