Flies are saving your chocolate cravings
Around 80% of Earth's flowering plants need animals to pollinate them - but it's not just bees getting the job done.
The movement of pollen from one plant to another is how flowering plants are fertilised. The majority, including many of those we farm for food, rely on animals for this process.
Bees may come to mind first when you think of pollination, but a large number of different animals also help, including butterflies, wasps, midges, birds, bats, and lemurs.
Watch as Dr Erica McAlister, a Diptera expert at the Museum, explains just how important flies can be as pollinators - especially for those partial to a bar of chocolate.
The midges maintaining cocoa crops
A bite from a female fly in the family Ceratopogonidae (biting midges) can be painful and irritating, but chocolate-lovers should consider being more forgiving.
These flies are primary pollinators of the cacao (or cocoa) tree, Theobroma cacao, the beans of which are used to make chocolate. One genus of midges, Forcipomyia (in which there are at least 1,000 described species), plays a key role in pollinating the tree's flowers.
Midges are almost alone in their responsibility, primarily because of their size. Forcipomyia are only around one to three millimetres in length. This makes them the perfect size to access the hooded, pollen-producing anthers of the cocoa tree's small flowers.
But there is a short window of opportunity for the flies to fulfil their role, with most of the flowers only lasting one or two days.
Cocoa trees are not the most efficient reproducers. Some have estimated that around one in 400-500 cocoa flowers will produce fruit, and only 10% to 30% of pods will reach maturity.
Is the future of chocolate at risk?
Chocolate has a rich history. Currently, the oldest evidence of its use by humans is around 7,000 years old. Residue of cacao beverages were found on a shard of a ceramic vessel.
It is thought that Europeans were first introduced to chocolate through a potentially similar beverage in 1519, when Spanish Conquistador Hernán Cortés travelled to the Aztec capital of Tenochtitlan, located in what is now Mexico City. Cacao was subsequently introduced in Europe and its popularity spread.
Today, cacao is big business, and the Central and South American native plant is farmed around the world. Côte d'Ivoire in West Africa produces around 40% of the world's cocoa beans. In 2016, the country produced more than 1,470,000 tonnes - although Ghana and Indonesia also ranked highly by production weight.
But the midges that keep the plants alive may be facing difficult times ahead. They are challenged by changing weather patterns, expansion of farming and the increasing number and prevalence of pests and diseases.
Cacao is a successful understory plant, growing to between six and 12 metres below the canopies of other trees in its native tropical rainforests. But to increase commercial production, farms often remove shading trees to make room for more evergreen cacao.
Midges prefer the shade, and their larvae thrive in damp conditions such as in rotten wood or composting leaf litter. It means they can be negatively impacted by this change, pushing the cacao pollination rate even lower than its already low starting point.
Unbeknown to the midges, a huge responsibility has been put on them. But an increase in demand for cocoa products appears to only be making life tougher for the small pollinators able to keep chocoholics happy.