The tiniest moths in the world
Discover the microscopic dimensions of the smallest moths on the planet.
With a wingspan of just 2.5 millimetres, the Stigmella maya is one of the most petite moths known to science. But just how miniature do you need to be to qualify as a micro-moth?
The scientific name for butterflies and moths is Lepidoptera. Museum curator David Lees specialises in the smallest species, microlepidoptera, and guides us through the intricate world of mini moths.
What is a micro-moth?
As you might have guessed from the name, most micro-moths are small. Many of them have wingspans measuring less than 20 millimetres.
Because they usually are so small, they are difficult to spot and we often have to dissect micro-moths and examine their genitalia to identify them.
There are about 1,850 species of micro-moth recorded in the UK, and at least 62,000 named worldwide. There are even more in the tropics that have not yet been given names by scientists.
How do we categorise moths and butterflies?
Moths and butterflies evolved from a common ancestor about 250 million years ago.
Traditionally, they have been split into three broad groups: micro-moths, macro-moths and butterflies.
Different families developed different characteristics, habits, colours and wing structures. Many species evolved in close company with the plants they relied on for food.
The micro-moths category includes all the species that evolved early - from about 250 to 200 million years ago.
Macro-moths are the moths that evolved more recently - from about 125 million years ago - as flowering plants also evolved.
Most macro-moths are large, and this group is technically called Macroheterocera. It contains the biggest species in the world.
Because the above categories are linked to evolutionary time rather than insect size, it creates some confusion: some micros are actually quite big, while some macros can be petite.
For example, the bentwing ghost moth from Australia measures a huge 25 centimetres in wingspan, but is still technically a micro.
How big is the world's smallest moth?
The current record holder is the Stigmella maya, and the forewing measures just 1.2 millimetres. It is found in Yucatan in Mexico.
This species is part of a group called microlepidoptera - the smallest moths and butterflies in the world.
Another very tiny moth, Enteucha acetosae, is found in Britain. The smallest individuals have a wingspan of about 3 millimetres and the minute larvae live inside sorrel leaves, often turning them from green to red.
It is possible there may be even smaller moths out there, but we haven't found them yet. When an insect is this small, it has a very specific lifestyle, which makes it hard to study.
What are leaf miners?
One of the weirder parts of that lifestyle is leaf mining. Leaf miners are larvae that are so small, they live inside the plant tissue.
Normally, you can spot caterpillars sitting on leaves and stems, munching their way through them.
But as leaf miners eat the plant from the inside, they can't be easily seen. However the damage they cause can often be spotted as lines and blotches all over the leaf.
Other small moth species eat almost anything you could imagine including fungi, wood and underwater plants. The diversity is really amazing.
What do we know about the evolution of Lepidoptera?
Several micro-moths are long extinct - including Archaeolepis, a 180 million-year-old fossil. It was found in Dorset and is preserved in the Museum.
We also have some species that are very ancient, but are still alive today, which is fantastic. One of these families is called Micropterigidae. You can find Micropterix calthella in Ranunculus flowers in early June. Micropterigids are preserved in amber going back 125 million years or more.
These tiny moths are unique because the adults have chewing mouthparts. They chomp pollen grains or fern spores and grind them in a sort of gizzard.
It is fascinating because nearly all other moths and butterflies have sucking mouthparts - the proboscis - for drinking nectar.
Where do butterflies fit in?
Butterflies are (in the evolutionary scheme of things) just big, flamboyant, day-flying micro-moths.
Their fossils go back 55 million years, but recent research suggests they could have originated in the time of dinosaurs - between 110 and 65 million years ago.
They certainly evolved later than the tiny moths. They developed techniques for flying in the daytime, instead of at night like many moth species do.
What's next for micro-moth research?
We still hope that new, what we term, living fossils might be discovered. These are butterflies and moths that evolved a very long time ago, but are still going strong today.
In 2015, an extraordinary example of this was discovered: a micro-moth family called Aenigmatineidae, from Kangaroo Island near Australia.
The Museum has just acquired two precious specimens of the Kangaroo Island moth, Aenigmatinea glatzella.
Its mouthparts are atrophied and it does not eat, so the adults live only a few days. The species is clinging on in Kangaroo Island, living on bushes in a part of the island out of the reach of bush fires.
Research has shown that the family evolved very early, probably before the flowering plants were around - so they did not need to drink nectar.
Instead, the caterpillars live in the stems of a cypress plant.
It just goes to show that we live in really exciting times for Lepidoptera research - and there is still so much more to discover.