The languidly drooping outer petals of WA’s endangered giant spider orchids (Caladenia excelsa) make this the largest Western Australian orchid, reaching 25cm in length and 15cm across. The smallest of WA’s orchids are Microtis atrata, reaching a mere 2mm in width.

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    The genus name of the forest mantis orchid (Caladenia attingens) is derived from the Greek words calos (meaning beautiful) and aden (meaning glands), referring to the colourful labellum and the glistening glands that adorn the middle of flower. Their shape and colour mimicking female insects, attracting male insect pollinators.

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    Dragon orchid’s (Caladenia barbarossa) insectiform lip closely matches the size, shape and
    texture of a female flower wasp.

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    A Zaspilothynnus trilobatus wasp trying to mate with a Drakaea glyptodon orchid. The orchids have evolved to release chemical copies of the females’ pheromones – and it can be irresistible. Back in 1928, an Australian amateur naturalist Edith Coleman became the first to realise that scent was key when it came to attracting the males.

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    In Australia, at least 250 species in some 10 genera have adopted a sexually deceptive strategy, deceiving male insects – mostly wasps – into believing that they’ve found an elusive female. Hammer orchids like the warty hammer orchid (Drakaea livida) with Zaspilothynnus nigripes wasp (left) are among the 10.

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    A warty hammer orchid (Drakaea livida) deceives a Zaspilothynnus nigripes wasp into thinking it’s a female wasp. Hammer, spider orchids, flying duck orchids and elbow orchids all use the same devious sexually deceptive approach. Europe has one or two groups of orchids that imitate female insects to lure pollinators, South Africa is home to a single group that does the same, and the USA has none. Australia has 10.

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    Australian Geographic photographer Esther Beaton captured eye gnats (Conioscinella duda) carrying pollen from the fringed midge orchid (Corunastylis fimbriata) – confirming a new scientific discovery.

    At an Aboriginal site called Bulgandry in the Brisbane Water National Park near Gosford, north of Sydney, NSW she photographed tiny flies with what looked like twin yellow plumes on their heads. Dan Bickel, an entomologist at the Australian Museum in Sydney, confirmed that the plumes were pollen, being carefully carried on the heads of eye gnats to the fringed midge orchid, a previously unknown mode of pollination for this orchid.

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    The main lip of the flower of a hammer orchid is an insect-shaped blob that is hinged part way along. When the wasp grabs the flower, the momentum flips the animal upside down and whacks it into the pollen. L – R: King-in-his-carriage (Drakaea glyptodon), dwarf hammer orchid (D. micrantha), glossy-leaved hammer orchid (D. elastica) and D. livida.

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    Cryptostylis (also called tongue orchids) are sexually deceptive – the orchids fool male Lissopimpla excelsa wasps into mating with the flowers and inadvertently transferring pollen. Attractive tongue orchids have the highest known pollination rate of sexually deceptive orchids, and the wasps are so enthusiastic in their pollination duties that they even ejaculate and waste their sperm on the flowers. The orchids have tactile elements (‘love handles’), colours and UV resembling female Lissopimpla excelsa wasps, but it is the scent of the orchids that the pollinators find irresistible. This scent is not detectable to humans.

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    Scented sun orchid (Thelymitra macrophylla) only opens up in warm weather and mimics the lily family hoping to attract the same pollinators.

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    Endemic to Australia rattle beak orchids (Lyperanthus serratus) make a distinct rattle sound when shaken, hence the name.

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    Scents are the orchids’ main tool for attracting male wasps, but once an orchid has lured a pollinator close, the colour of the petals and ultraviolet spots, like those seen on this purple enamel orchid (Elythranthera brunonis, left) can make the flower harder to resist. The ultraviolet spots create an illusion, resembling the UV reflected from the wings of female wasps.

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    Forest mantis orchid (Caladenia attingens) is part of a family with a huge variation of form and colour, leading to an array of hybrids. Recent taxonomy revisions have increased the number of species to over 300.

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    The alluring curves of this endangered giant spider orchid (Caladenia excelsa) serve an important purpose. When a male lands on the flower, its shape ensures he grips it in just the right position to make contact with the pollen.

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    The Caldenia genus of the endangered giant spider orchid (Caladenia excelsa) are mostly distributed across southern Australia, although there are four species in New Zealand and another extends to New Caledonia, Indonesia and Malaysia.

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Gallery: Orchids of deception

By AG STAFF | November 29, 2013

More so than anywhere else in the world, our orchids are deceitful temptresses with a powerful perfume.