A fishing spider on a basement floor in Troy. Dana Wilde photo

Jack, my grandson Silas’ dad, does not like spiders. But he plays along with us when we’re out spider (and toad, frog, millipede, sowbug, salamander, turtle, etc.) hunting, and sometimes points out small crawling things to us, which Silas usually pounces on and corrals in plastic containers.

So this weekend, it was Jack who called to us from the basement, in a voice that was not alarmed, but definitely not casual.

“Guys, there’s a spider down here,” we heard him say. Then he added, “A big spider. A really big spider. It’s HUGE.”

Silas scrambled for the cellar stairs. I picked up a large-size vial for captivation purposes and followed.

Jack was right. On the concrete floor was the biggest fishing spider I’ve ever seen. Its body was the diameter of a quarter, about an inch, and the legs splayed out still further.

Fishing spiders (family Pisauridae) are just about the biggest spiders we have in Maine. Some orb weavers (family Araneidae) get pretty big, especially the barn spiders (Araneus cavaticus), which spin sometimes huge webs in places like barns. (I once came upon a barn spider in a web spanning about 7 feet from an overhead cross beam to near the bottom of a post in a barn in Unity.) And the fishing spiders’ family relatives, the nursery web spiders, can get pretty large, too. But the fishing spiders tend to be the largest hereabouts.

Sometimes known as wharf, dock or raft spiders, four species are fairly common in Maine: Dolomedes triton (also known as the six-spotted fishing spider), D. scriptus, D. striatus and D. tenebrosus, which sometimes wanders into houses and was the female individual we found on the cellar floor.

Among fishing spiders, the females are normally larger than the males, and D. tenebrosus females can be up to twice as large. There’s a myth about female spiders eating the males after mating, which in reality happens, for the most part, only about 5% of the time among many species. But among fishing spiders, the female eats the male pretty much every time, according to studies. The evolutionary advantage of sexual cannibalism is not known for sure. One theory is the females are simply hungry. It happens more commonly among species with greater size dimorphism, as with Dolomedes.

Fishing spiders spend most of their lives hunting near, on or in water. They might overhang the shore of a pond or slow-moving stream on a strand of silk, watching for motion and listening for air and water vibrations set up by bugs, and in some cases even tadpoles or minnows. They can also walk on water, similar to some wolf spiders and long-jawed orb weavers. They use a kind of rowing motion with their middle pairs of legs. When a burst of speed is needed to run down an insect or escape a predator, they kick into a sort of galloping stride across the surface, covering up to 20 inches very quickly. Some of them also use their bodies to catch a breeze and sail across the water.

Fishing spiders sometimes fully submerge, and studies have shown that their eyesight remains reasonably good underwater. Their bodies have a “cuticle,” or outer covering of a waxy, water-repelling substance that, combined with dense hair, keeps them dry.

I’ve seen most of my fishing spiders inside the house. They’re usually resting on a door frame or a window screen, watching for prey. One night, I awoke to see a huge D. tenebrosus on the bedroom wall a few inches from my face. She was unmoving, like the one on the cellar floor.

The legs of the one on the floor were so long they could not fit into the vial without a risk of injury. Finally, Silas found a baby food jar. The legs were still wider than the jar mouth, but we gently lowered the jar over her, and she pulled in her legs. We corralled her by slipping a piece of paper under the upside-down jar and then turning the jar right side up. When she fell to the bottom, we put the cap on.

Jack kept shuddering, so Silas set the spider loose outside, where she crawled partway up the door frame.

Dana Wilde lives in Troy. You can contact him at dwilde.naturalist@gmail.com. His book “A Backyard Book of Spiders in Maine” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.