A new species of arachnid has joined the daddy longlegs ranks, with researchers dubbing the giant Cryptomaster behemoth. The species had gone undiscovered until now because it is a notoriously elusive creature, skittering beneath the leafy debris and logs that litter the forest floor of southwest Oregon. The findings are published in the journal Zookeys.

Although the creature seems undeserving of its dramatic name – it’s a mere 4 millimeters (0.15 inches) wide – it actually looms large over those in its same suborder. Its closest cousin is the Cryptomaster leviathan, also relatively large, except for one jarring difference: Two spines on the penis of the C. leviathan. The C. behemoth lacks this pointed difference.

(C) and (D) show a lateral view of the penis. (E) and (F) show a close-up view of the two spines. Starrett et al, Zookeys 2016

To uncover if there were more differences than just genital anatomy, the researchers extracted DNA from both species. Once again, the creatures thwarted all expectation: Although the C. leviathan has a wide range of habitats, it has little genetic diversity. On the other hand, C. behemoth has a limited habitat range, but greater genetic diversity than its cousin.

These two “monster” arachnids do share a commonality, though: They both come in two different sizes, with some growing quite large while others remaining quite small.

"The basis for these two forms is unknown – the different forms can be found in both sexes, in both species and from the same localities,” wrote the researchers in their paper. “Additionally, the two forms are not genetically divergent.”

Although similar in appearance, daddy longlegs (otherwise known as harvestmen or Opiliones) are not actually spiders, but arachnids. This new species joins 4,100 others in the suborder Laniatores. The latest find, according to the researchers, reinforces the genetic diversity of Oregon’s mountainous southern terrain.