Which of Darwin's finches uses cactus spines as tools to extract insects?

The Darwin’s finch that uses cactus spines as tools to extract insects is the woodpecker finch.

The woodpecker finch, Camarhynchus pallidus, lives in the Galápagos Islands and uses twigs, sticks, and cactus spines to reach prey hidden in tree bark. It may push a larva from a crevice, spear slow-moving prey, or prod an insect until it emerges. Birds can shorten or reshape a tool to make it easier to handle.

This behavior helps the finch exploit a niche normally associated with woodpeckers, which are absent from the Galápagos. In dry habitats, tool use can provide as much as half of the bird’s prey, especially when insects and larvae are concealed in wood.

Tool use is not equally common everywhere. Woodpecker finches in wetter areas often find prey without tools, while those in arid zones use them more routinely. Researchers have found both inherited predispositions and evidence of learning, including juveniles copying adults using novel barbed twigs.