In Darwin’s Footsteps
We were lucky enough to see Darwin’s moth (Xanthopan morganii ssp. Predicate), which played a major part in the breakthrough of the theory of evolution. The existence of this large hawkmoth ( from the family Sphingidae) was predicted by Charles Darwin in 1862 upon seeing the enormous spur of the beautiful white orchid Angraecum sesquipedale. Knowing that hawkmoths were important pollinators of many plant species, Darwin assumed that the nectar in the 35 cm long spur of this orchid could only be reached by a species of hawkmoth with an equally long proboscis that had co-evolved with this orchid. If this would not be the case then the ridiculously long spur of the orchid would not make sense in the light of Darwin’s theory of evolution. He was only proven right in 1903.
A lot of research has been done since, trying to relate orchid species to their respective pollinator hawkmoths. However interesting this research may be, the focus of our expedition is to do a general survey of biodiversity in different taxa, among which are three families of moths. The goal is to identify as many moth species as possible using a light trap. The setup we use for attracting moths consists of a bright 125 watt HPL bulb, strung up in front of a white linen sheet (that has unfortunately turned into a not so white and soaked linen sheet after the first few nights) and a plastic ground sheet to intercept moths and beetles bumping off the linen.
Sphingidae or Hawkmoths are usually large, jet-shaped moths. These good flyers can cover quite some distance in their search for nectar. Some species are diurnal and could be mistaken by the unwary observer for a tiny hummingbird when hovering in front of a flower. We chose to look at Hawkmoths because they are a well-known family, making identification easier and because they play a well-defined pollination role in the ecosystem, making them ideal indicator species.
The family of Saturnidae or Emperor moths holds some of the world’s largest moth species such as the Atlas moth and the Madagascar lunar moth. These hairy moths have unusually large and heavy abdomens (full of eggs or sperm) which, together with their lack of mouthparts and short adult lifespan makes them rather poor, short-distance flyers. Again this family is relatively well known, making identification easier.
Geometridae or Geometer moths are a much lesser known group of moths, making identification up to species level a challenge but meanwhile this gives us a good chance of finding a new species. Morphologically they somewhat resemble butterflies, resting with their wings spread.
Shining our torches up in the canopy shows that many moths are active in the canopy layer and fewer seem to roam the undergrowth. Therefore we try to maximize the amount of light form our trap that reaches the canopy by looking for clearings in the forest or ridges overlooking the canopy to place our trap. Sometimes hiking an hour or more through the darkness to the ideal spot, generator and light gear in tow. The spots where we could overlook the canopy are by far the best, with over 100 hawkmoths and other species on the tiny sheet in four hours of running the trap! Although the rains did not allow us to run the light trap for a full night we did find species of all three moth genera on every try. It is exciting exploring these lesser known elements of biodiversity and one wonders at what is still waiting to be revealed...