Small spiders have brains in their legs

The brains of tiny spiders are so large they fill their body cavities and overflow into their legs. To investigate how miniaturisation affects brain size and behaviour, researchers studied the central nervous systems of nine spider species.

The researchers found that as the spiders get smaller, their brains get proportionally larger. In the case of the smallest spiders, their brains can fill almost 80% of their total body cavity, including a quarter of their legs.