Tarantulas discovered on Tucker nuck

COURTESY PHOTOS A purse web spider Tarantulas are on Tuckernuck Island.

Andrew McKenna-Foster and Cheryl Comeau Beaton, Maria Mitchell Association spider experts, have discovered an inch-long cousin of the giant tarantula on Tuckernuck, an island off the western tip of Nantucket.

McKenna-Foster reported his and Beaton's findings on the purse web spider at the daylong 3rd Annual Nantucket Biodiversity Conference that was held recently.

Aware of the purse web spider's range from Florida to Block Island, Beaton and McKenna-Foster confirmed the purse web spider presence on Tuckernuck Island.

"We know from arachnologists that they're also found on Martha's Vineyard and we heard that they [might be] on Tuckernuck," he said. "Cheryl and I were on Tuckernuck in 2006 collecting spiders for a species survey and Cheryl found one of these tubes and we were very excited and we started finding them everywhere. We were walking on them and seeing them everywhere on the island."

The tube, woven of the spider's silk, is the origin of its name. This spider spins a cylindrical purse-like tube of silk about six inches long that descends through grass or leaf litter into the ground that the purse web spider uses as a trap to kill its prey with its giant fangs.

Andrew McKenna-Foster takes a class from the Maria Mitchell Association on a spider hunt. To see this spider on the slides that McKenna-Foster showed, one would think they were looking at the larger, more famous tarantula that can grow to six inches or more.

Differentiating tarantulas, large or purse web, from other spiders is easy, explained McKenna-Foster because of the spider's fangs. All other spiders have fangs/mouthparts that reach around from either side like a person holding their arms level and bringing their hands together.

But tarantulas and their relatives have fangs that jut upward and are drawn back to be brought down on their live food victims. In the case of the purse web spider, it hides in its silk "purse" and when an insect or worm passes over it, the spider sinks its fangs into its victim from within the purse and pulls it in close to kill and eat it.

Elated to discover this species new to Nantucket's archipelago, McKenna-Foster set up transects within two study areas — one each on the eastern and western sides of Tuckernuck — to walk along to count spider purse tubes. He and Beaton also did three random walks for two meters each in three directions in each study area. What they discovered is that these spiders tend to cluster their purse webs together in areas where Pennsylvania sedge, huckleberry and bayberry are growing. McKenna-Foster found around 100 webs in the western side of the island about 343 on the eastern side where webs were so dense that they continued out of the study area. I