How a Daddy Longlegs Grows Such Strange Legs

Scientists have identified genes that make a harvestman arachnid’s appendages able to twirl like a monkey’s tail.

The harvestman makes its way through the mossy woodland on eight spindly legs, delicate tentpoles supporting a plump body with two tiny eyes. These arachnids, sometimes called daddy longlegs, are cousins of spiders whose outdoorsy lifestyle sets them apart from the other creatures called daddy longlegs, which are more properly known as cellar spiders. They have other curious differences, too: The tips of a harvestman’s elegant limbs are flexible, allowing them to wrap around a twig like a monkey’s tail. Harvestmen’s distance from spiders has made them appealing to geneticists curious about how arachnids evolved. In a paper published Wednesday in the journal Proceedings of the Royal Society B, researchers who sequenced the harvestman genome reported that the arachnids differ in key ways from spiders, and they described how certain genes tell those trademark legs how to grow. The size of the harvestman genome was the team’s first focus. Ancestors of contemporary spiders experienced a duplication of their entire genomes at some point long ago, giving them more genes for evolution to work with. This might have contributed to greater diversity among spiders.