Spider orchids have a hinged labellum that can either swing towards or away from the column.

It is counter-balanced and closes with the weight of the insect as it moves closer to the base.

The column flaps hang like curtains in front of the pollinia (see photo right) and as the insect pushes forward, it holds them shut.

When backing out, the insect parts the flaps and this permits the pollinia to drop on the insect's back which has been made sticky when making contact with the stigma.

The calli work as a 'ladder' giving a foot-hold for the insect and assists with its balance to ensure that the insect's body enters without contacting the stigma or anther.  (see photo left)

The same balance assistance also ensures that the insect cannot leave without touching both in the right order.


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