We’ve passed the darkest part of winter and the first orchids of spring are blooming in Australia. This week we have Caladenia crebra, the Arrowsmith Spider Orchid. You’ll find it flowering in August and September, in Western Australia, north of Perth.
It’s the long thin petals and sepals that give a spider orchid its name, in English, because they are said to look like spider legs. The Latin Caladenia comes from the ancient Greek, kalos, beautiful and aden, gland for the labellum, the colourful lower petal. The labellum in spider orchids has calli. These are small projections on the labellum, and some of the photos on iNaturalist really show these off. The calli in the photos here are the maroon growths on the green labellum. The crebra part means crowded, and refers to how many calli there are on the labellum of this plant, which makes it so distinctive.
These calli are part of a lure for the orchid’s pollinator. Caladenia crebra attracts the wasp Campylothynnus flavopictus specifically male wasps. The female wasps are flightless so not really of use to the orchids as a pollinator. But they are useful to mimic because the flower isn’t offering food, it’s offering sex. A female wasp crawls to a prominent place, and waits while she releases pheromones. The labellum is enough to look like a female wasp. It helps that the orchid also copies key elements of the smell.
Caladenia crebra produces an irresistible scent from its sepal tips. A study found that the attraction was down to four chemicals, (methylthio)phenols, that the authors described as “extraordinary strong pollinator attractants”. Around a third of the wasps that approach the flowerattempt to mate with it. As the wasp wrestles with the labellum, it can get slapped with pollen to take to another plant.
It was discovered in sandy soil and scrub south of Dongara but it’s not clear for how much longer it will be there. Typically, distributions of Caladenia are expected to be broadly stable over the next 50 years, but Caladenia crebra, along with C. harringtoniae and C. infundibularis may face a contraction. However, with Caladenia crebra relying on a specific pollinator, it’s not just the orchid’s ability to cope with increasing heat that’s in question.
If you want to see it in the wild, now is the time, but you’ll have to be in Western Australia, as it’s found nowhere else.
Cover image: Caladenia crebra by Jason CC BY-NC
