In the world of Australian orchids it is less a survival of the fittest and more a survival of the sexiest!
With a cheeky smile, orchid hunter Terry Dunham, points to the unusual looking flower on a sandy patch of ground at Tozers Bushcamp in WA’s southern coast. The warty hammer or Drakaea livida, is not a classically beautiful orchid like the colourful queen of Sheba, also growing at Tozers. Instead, its liver coloured body, sways tentatively on a thin green stem like a dark and furry insect, which is exactly what this seductive orchid is counting on.
‘It’s all game of sexual deception,’ says the wildflower expert.
Like many West Australian orchids the warty hammer makes use of its unusual morphology to attract a pollinator that will ensure its survival; in this case the male thynnine wasp. This libidinous male wasp flies around looking for a flightless females to lift, carry off and mate with in mid-air. The warty hammer, mimicking not only the shape of the wasp but also its powerful pheromones, lures the unwitting male wasp to land on its hinged lower lip or labellum.
’(The male) sees one of these…he grabs hold of that and the column flips over and whacks him on the head...’ The unwitting male then goes off looking for another ‘female’ and transfers the pollen, repeating the process.
Over 250 orchids in Australia rely on their ability to imitate the scent of a fertile female to trick a male pollinator. In 2017 scientists from the University of Western Australia identified some of the sulphur-based chemical compounds used by spider orchids, Caladenia sp., to lure the males in.
Some orchids, like the bird orchid (Pterostylis barbata) have an even more sophisticated system that entraps the male insect, this time a male gnat. The gnat is lured by the scent, gets trapped inside the flower and has to crawl through a narrow opening ensuring it is well-covered in its pollen.
These fascinating examples pollinator-flower interactions exemplify the Darwinian theory of co-evolution but prompt the question: in the world of orchids is it the fittest or the sexiest who survive?