Nearly 20 years before he published On the Origin of Species, Charles Darwin
started to study orchids, intrigued by the extraordinary features of their flow-
ers. He examined British species, and he grew tropical species, solicited from
horticulturists, in his greenhouse. In 1862, in his first book after On the Ori-
gin of Species, he summarized his studies in On the Various Contrivances by
which British and Foreign Orchids are Fertilised by Insects, and on the Good
Effects of Intercrossing. It is a landmark work, in which Darwin put into practice
his principles of natural selection and descent with modification. Parting with
the prevailing theological interpretation, that flowers were shaped by God
to inspire us with beauty, Darwin showed that the astonishingly diverse and
peculiar features of orchid flowers increase the chance that they will attract
insects and deposit pollen on them in so precise a way as to ensure cross-
pollination. Among these remarkable plants was a species from Madagascar,
Angraecum sesquipedale, with a nectar-bearing tube up to 30 cm long (FIG-
URE 13.1). Other plants with much shorter nectar spurs are visited by insects
with tongues long enough to reach the nectar, so Darwin predicted that there
must exist in Madagascar a moth with a similarly long proboscis. One reviewer
ridiculed this idea, and indeed the very idea that the features of flowers are
useful, but in 1903 a sphinx moth with a proboscis up to 30 cm long was
described from Madagascar, and was fittingly named Xanthopan morganii
praedicta. Angraecum and its moth perfectly illustrated Darwin’s speculation
(in On the Origin of Species) that both a flower and a pollinating insect “might
slowly become, either simultaneously or one after the other, modified and
adapted in the most perfect manner.”Red-billed oxpeckers (Buphagus erythrorhynchus) like the one shown here on a
Cape buffalo (Syncerus caffer) spend most of their time on large African ungu-
lates, where they eat mostly ticks, but also feed at open wounds. Their interac-
tion with the mammals is on the border between mutualism and parasitism.Interactions
Interactions among Species
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