Spider orchids

There are over 100 species of orchids in New Zealand. Some of them are epiphytic (live on trees), while others are terrestrial and are usually found on the forest floor or among scrub. Spider orchids are one of the most common and widespread terrestrial orchids in New Zealand. They are found from coastal to alpine areas and generally in shady and damp areas.

Spider orchids are classified in the genus Corybas. About 16 species occur in New Zealand; some of these are also found in Australia. These orchids are very small. They have only one leaf, usually not bigger than 3 cm across, and one flower. The flowers are not very colourful and lack nectar. Their sepals and petals are very long and thin, and they are usually pointing forward or upwards, almost like the legs of a spider ready to attack!

Orchid flowers are generally pollinated by insects. However, the insects that pollinate spider orchids had remained a mystery for years. Since the early 1900’s findings of dead fungus gnats inside spider orchids’ flowers have puzzled orchid enthusiasts and scientists alike. These tiny flies are less than 5 mm in length. Similar to spider orchids, fungus gnats are found in dark and moist habitats. As the name suggests, they are common on fungi, which is their favourite place to mate and lay their eggs.

My three-year study, funded by The Royal Society of New Zealand’s Marsden Fund, has revealed these orchids employ a specialised pollination system unprecedented for New Zealand. Spider orchids are fooling fungus gnats into visiting and pollinating their flowers, possibly by looking and smelling like mushrooms. This deceptive pollination system is known as brood site deception and exploits the reproductive preferences of fungus gnats. Our video footage revealed that male and female fungus gnats mate on the leaf or flower of these orchids. After copulation the female searches for a suitable spot to lay her eggs. We believe that it is during this search for a suitable spot that the pollen is removed and fertilisation of the flower occurs.

Genetic analyses of fungus gnats’ eggs and larvae found on the flowers suggest different species of spider orchids growing together side by side attract different species of fungus gnats, possibly by emitting a slightly different aroma. Testing this hypothesis is one of the goals of future studies.

Meanwhile, one of my recent studies on the diversity of these orchids, funded by the Australian Orchid Foundation, has provided support to recognise five new species of spider orchids for New Zealand. Three of these species are common and can be found in several places across the country. The other two species are uncommon, and one of them is only known from a single locality.

The Royal Society of New Zealand’s Marsden Fund.

Australian Orchid Foundation.