What you see ain’t always what you get
Most flowering plants offer a reward for insects and other animals in the form of nectar when they visit a flower. With orchids deception is fairly common. But how do they do it… and why?
The first is the simplest method of deception that orchids sometimes employ- they simply pretend to be a plant that offers sweet nectar to drink. This is well employed in several species of sun orchid (Thelymitra) found in Australia. They only flower for one or two days a year, usually the first hot day of November in the south of Australia. Before then the flowers stay closed, and after that day or two in the sun they close and shrivel. The other interesting thing about sun orchids is that some are capable of producing blue flowers- a very rare ability for an orchid. The flowers they may mimic are usually lilies such as the blue flax lilies and the chocolate and fringe lilies that are all in flower at the same time. Some species of sun orchid are even self pollinating and if there are no hot days when they are ready to open, they simply self pollinate and shed seeds anyway. They rely on insects like bees picking up on the ultraviolet signature of the flower, visiting and flying away, ripped off by the lack of something to drink. If the bee lands on another flower, the pollen it picked up will be transferred and cross pollination can occur. What would the flower do this for? They live on poor soils and making nectar is expensive, so they make themselves look pretty but have nothing to offer, and the insect doesn’t know until it visits.
The second method of deception is far more primal. In this case the flower offers much more and definitely doesn’t deliver. Meet the green combed spider orchid (Caladenia dialatata). It employs a method that is surprisingly common among orchids… real seduction with no reward.
In the southern hemisphere springtime, many insects emerge, and among them are a number of wasp species. They are not communal like wasps most people are familiar with, but eggs laid the year before under the ground have hatched and the larvae have pupated. The adults dig their way to the surface, first the males, then the females. The orchids take full advantage of this delayed timing. As the males are already out, they are patrolling for the wingless females which climb up grass stems and await a winged male to literally carry them off. But the orchid flowers just before the female wasps are due to emerge. The orchid bears a resemblance to the female wasp and even mimics the smell. The desperate males only have a short time to find a mate so they will go for anything that looks remotely like one. They tackle to flowers, landing on the labellum (the ‘lip’ of an orchid flower) and trying to carry it away. It is hinged so the confused male wasp swings upward and collects a head of pollen. He eventually realizes it is a case of mistaken identity and flies off. If he is fooled again by another flower the process is repeated and the flower is pollinated.
This is by no means restricted to spider orchids – many orchids rely on a specific wasp or bee species to be fooled into trying to mate with them.