Halloween is the season for candy, wearing costumes — and for spiders.
More than 200 species of spiders live in the Hawaiian islands. Half of them are found nowhere else in the world. Spiders in Hawaiʻi share a unique evolution due to their geographic isolation.
This story focuses on three types of spiders that are endemic to Hawaiʻi, and perfectly Halloween-themed.
Tetragnatha (long-jawed spiders)
The spider genus Tetragnatha (also known as long-jawed spiders) can be found all over the world — but some of the species endemic to Hawaiʻi learned how to live outside of the web and live the life of a hunter.
There are 50 to 60 species of Tetragnatha spiders living in Hawaiʻi. Over time, a few Tetragnatha spiders in Hawaiʻi abandoned the art of web-building, and their bodies lost the spigots that make sticky silk.
Rosemary Gillespie is a professor at the Department of Environmental Science, Policy, and Management at the University of California, Berkeley.
"In California, or in Scotland, or wherever, you’ve got all sorts of groups of spiders that do not build webs. But the really super cool thing is that in Hawaiʻi, you don’t have those groups of spiders at all," Gillespie said.
"Instead, you got this genus that ancestrally built these orb webs. So we can just exploit that niche," Gillespie told HPR.
With landmasses to explore without getting attacked by other spiders, some of the Tetragnatha spiders left the web, and adapted to become incredibly fast and stealthy killers.
Theridion grallator (Hawaiian happy-face spiders)
If you have arachnophobia and a fear of clowns — beware of the Hawaiian happy-face spiders.
They have a colorful pattern of red, yellow, black, and sometimes white on their bodies.
Despite the name, only a third of the species have an eerie grin on their back. Most of them have a random assortment of spots.
Brad Reil, a graduate student researcher in the entomology program at the University of Hawaiʻi at Mānoa, says the reason behind the different patterns could be a tactic to confuse predators.
"If all of the spiders had that pattern, it would be very easy for the predators to develop that search image, and they would get very good at hunting for the spiders. So over time, certain individuals have evolved this happy-face pattern that breaks up the search image," Reil explained.
Happy-face spiders can be found sticking to the underside of large leaves during the day, and forage at night. They reside on Oʻahu, Molokaʻi, Maui, and Hawaiʻi.
Ariamnes (Stick Spiders)
Ariamnes is a genus of spiders with long, flexible abdomens. Their bodies help to camouflage, but other reasons for their long abdomens are unknown.
These nocturnal creatures can be found roaming through the night in high elevations on every Hawaiian island.
Ariamnes are free living. They do not spin webs or practice kleptoparasitism — leeching onto other spiders' webs for food. Instead, they stroll around the forest floor in search of food.
Small but mighty, these creatures have an appetite for other spiders.
Unlike the hunter-type Tetragnatha spiders who learned to run quickly to catch their prey, Ariamnes live by the phrase, "Slow and steady wins the race."
UC Berkeley's Rosemary Gillespie says their hunting strategy is designed specifically for larger spiders, not insects. They move slowly and stalk their prey. Once they are close enough, they bite the prey and sink powerful venom into the soon-to-be corpse.
