Microscopic Crab-Like Creatures Discovered in Murder Cave

A rare species of tiny crab has potentially been found living in two caves, one of which was once linked to murders by an infamous 16th-century highwayman.

These tiny stygobitic crustaceans are only around 1mm (0.04 inches) in size, and were found residing in pools of water within two Scottish caves: Smoo Cave in Sutherland and Allt nan Uamh Stream Cave in Assynt.

According to a study published in the journal Cave and Karst Science, the crabs were discovered as a result of a preliminary expedition sampling 32 caves across various regions in Scotland over the course of six years. Researchers still need to confirm if these crabs belong to a species that has been found elsewhere in Europe.

smoo cave
Stock image of Smoo Cave in Scotland. A rare species of microscopic crab was potentially found in this cave and another nearby, marking the first time this species has been found in the British Isles. iStock / Getty Images Plus

Stygobites are usually obligate, meaning that they exclusively live in subterranean habitats. They are usually found in the underground water table, in aquifers, springs and the hyporheic zone of rivers (the porous sediment beneath a stream bed where the shallow groundwater and surface water mix), which is a strange and unique habitat. This is a field of science that has a lot of unknowns: we don't know a huge amount about the basic biology and ecology of groundwater-dwelling animals, the potential range of ecosystem services that they provide, nor how pollution and other human-caused disturbances will affect them.

The two caves where this species were possibly found are well known in the area, with Allt nan Uamh Stream Cave containing a popular caving network, and Smoo Cave being associated with up to 6,000 years of Scottish history, having been thought to be used by some of the earliest settlers in the region.

Smoo Cave is best known for being the site where famed highwayman Donald McMurdo is said to have disposed of his victims' bodies, throwing them into a blowhole in the cave.

The species of crab found in these caves potentially represent the first sightings ever in the British Isles.

The study authors say the species of crab they found may be the same as has previously been discovered in wells, streams and springs, as well as a forest pool, in Europe.

Lee Knight, lead author of the study, told the BBC: "[Stygobitic] creatures live entirely below the earth's surface and preliminary findings show that one particular ostracod could be the first recorded in Scotland. The specimens have been tentatively identified as Fabaeformiscandona latens from Allt nan Uamh Stream Cave and Smoo Cave, these are of importance because records of this genus are very rare in Britain."

The team said the expedition in the cave was "purely descriptive in nature, with no attempt to assess population levels aside from the relative abundances of various species within the communities."

"Most caves, with the exception of a few larger systems, were sampled at single locations only and on a single visit," they wrote. "The collection of further material is required for confirmation."