Disa ferruginea is one of the more conspicuous orchids found on the Klein River Mountains. The bright reddish-orange flowering spikes are easy to spot from a distance and, unlike many orchids, reliably flower even when there has not been a recent burn. The individual flowers are clustered at the top of the spike, each with a hooded upper sepal and a long upward-pointing spur, so that they resemble brightly coloured pixie hats. At first glance, such flowers would suggest a rich nectar source and would therefore be attractive to insects. In reality, they offer only the appearance of a reward.
Like many orchids, Disa ferruginea produces no nectar. Visiting insects receive nothing for their efforts. Instead, the plant presents a convincing imitation, closely matching the colours of nearby nectar-producing species and drawing in pollinators that have learned to associate those colours with food.
In the Cape mountains, many red and orange flowers are pollinated by the Mountain Pride Butterfly (Aeropetes tulbaghia). This butterfly regularly visits nectar-producing plants such as Tritoniopsis, Watsonia and Kniphofia, which include species in these colours that offer a reward. Disa ferruginea takes advantage of this by closely matching those colours to deceive the butterflies.
Studies by Newman, Anderson & Johnson (2012) have shown that in areas where red flowers dominate, such as Tritoniopsis triticea, the orchid is typically bright red; where orange flowers are more common, such as Kniphofia uvaria, the orchid develops an orange form. This colour matching is part of a highly effective imitation. The butterfly prefers the colour of local nectar plants and is more likely to visit orchids that resemble them.
In experiments where red and orange flowers were moved between sites, butterflies consistently chose the colour that matched the local nectar plants rather than the unfamiliar one. This suggests that the orchid is closely tracking the preferences of its pollinator, refining its imitation to match local species. For butterflies moving rapidly from one plant to the next in search of nectar, there is little to distinguish between those supplying nectar and those that do not. While most visits are to genuine nectar sources, occasionally the imitation is convincing enough to draw the butterfly to the orchid. In doing so, it unintentionally transfers the pollinia, allowing the plant to reproduce without expending resources on nectar.
On the Klein River Mountains, Disa ferruginea is often found growing alongside Tritoniopsis triticea and Watsonia schlechteri, and here the red-flowered form dominates. Occasionally, however, an orange-flowered form also appears, which may be more effective in attracting butterflies seeking nectar from Kniphofia uvaria. In this setting, the orchid appears to employ more than one form of imitation, matching whichever colours are most effective at attracting its pollinators.
