The experts at London's Natural History Museum pride themselves on being able to classify and display thousands of species - from birds and mammals to insects, dinosaurs and snakes - and are confident can identify most living things on the planet.
Except for a tiny red-and-black bug that has appeared in the museum's own gardens.
The almond-shaped insect, about the size of a grain of rice, and was first seen in March 2007 on some of the plane trees that grow on the grounds of the 19th-century museum, collections manager at the museum, Max Barclay, said Tuesday.
Within three months, it had become the most common insect in the garden, and had also been spotted in other central London parks, he said.
The museum has more than 28 million insect species in its collection, but none is an exact match for this insect. Still, Barclay was cautious about calling it a new discovery.
"I don't expect to find a new species in the gardens of a museum," he said. "Deep inside a tropical rainforest yes, but not in central London."
The bug resembles the Arocatus roeselii, which is usually found in central Europe but is a brighter red and lives on alder trees.
Entomologists suspect the new bug could be a version of the roeselii that has adapted to live on plane trees, but acknowledged it could be an entirely new species.
Either way, it appears the museum's tiny visitor, which appears harmless, is here to stay.
"We waited to see if the insect would survive the British winter," Barclay said. "It did and it's thriving, so now we had better figure out what it is."