Photo: Six-spotted Fishing Spider (Dolomedes triton), Judy Gallagher
Judy Gallagher is an ASNV board member and a regular surveyor of local wildlife who also captures photos of what she sees, in particular the less common species.
Six-spotted Fishing Spider (Dolomedes triton) on water, Judy Gallagher
I will never forget the first time I saw a large spider sprint across the surface of a pond. At the time I thought that I was seeing amazing yet aberrant behavior, but I later learned that this is normal for fishing spiders.
Banded Fishing Spider (Dolomedes vittatus) mother with nursery web and egg sac (white blob behind the spider), Judy Gallagher
Fishing spiders are members of the Pisauridae family, the Nursery Web Spiders. As the name suggests, when spider eggs are close to hatching, the female builds a tent-like "nursery" web, puts her egg sac inside, and stands guard to protect her young.
Banded Fishing Spider spiderlings, Judy Gallagher
Here's a picture of the "children" in their nursery (above). Aren't they cute?
Fishing spiders use spider silk to build their egg sacs and nursery webs and for lines to keep from being carried downstream. They do not use webs for prey capture however. They are roaming predators, hunting down their prey. Local fishing spiders are members of genus Dolomedes. There are about a hundred species worldwide, and we have five species here in Virginia.
Dark Fishing Spider (Dolomedes tenebrosus), well camouflaged against a streamside log, Judy Gallagher
White-banded Fishing Spider (Dolomedes albineus), Judy Gallagher
As their common name suggests, most fishing spiders are found in and around ponds, streams, lakes and wetlands. There is a local exception. White-banded Fishing Spiders are found on tree trunks, not by the water.
Fishing Spiders usually have long legs and a fairly flattened body which helps them to move across the water's surface. They are typically well camouflaged for their natural habitat. They occupy an ecological niche that is unusual for spiders.
Six-spotted Fishing Spider (Dolomedes triton), Judy Gallagher
They often hunt at the edge of a pond with some of their legs in the water as shown above. They detect ripples when insects land on or fall into the water, and run across the water to inject venom into their prey. Sensing the ripples in the water is similar to a web-building spider detecting vibrations when an insect lands on its web. Fishing spiders also can catch aquatic insects, small fish or tadpoles. They eat up to 5 times their weight in a day, so they have to be good predators.
Fishing spiders also can be prey and are eaten by fish, frogs, snakes, birds and even some large aquatic dragonfly larvae. There is a spider wasp that specializes in fishing spiders, capturing them, paralyzing them with a sting, and caching them alive to serve as food for the wasp's young. The wasp also can walk on water, something that I hope I am fortunate enough to see one day.
Fishing spiders' hairy bodies are hydrophobic, meaning that they repel water. This helps keep the spider from sinking, and it can also go beneath the water. Air trapped within its hairs allows it to stay under water for up to half an hour.
Fishing spiders have three speeds of locomotion. They can "skate," with each leg moving in its own small indentation, never breaking the water tension. They can move faster by using their second pair of legs like paddles, or even faster by lifting each leg and pushing it into the water. The opposing force of the water propels it forward quickly.
Dark Fishing Spider, Judy Gallagher
Most fishing spiders live for two years. They hibernate during their first winter, and I sometimes find them when turning over logs in the winter. Seeing a spider that is 3-4 inches long including the legs can be rather startling, but they are not aggressive to humans.
When the female is mature, she lays a pheromone-infused silk line to attract males. The male spider must carefully make vibrations different from those insects make, lest he be eaten before mating, but the female frequently eats the male after mating anyway. As I mentioned previously, females lay their eggs inside a silk sac, and they carry the sac with them. Unlike wolf spiders, which carry their sac with their hind legs, fishing spiders carry their egg sac with their jaws. This allows the mother to keep her head above water, but she can't eat during this time, as her jaws are otherwise occupied. The egg sac is waterproof.
Fishing spiders rarely bite, and their venom isn't strong enough to pose a threat to humans. But it would be wise to avoid harassing a female spider with an egg sac. They usually avoid humans, and they play an important role in controlling aquatic insects.
View more of Judy’s Observations from Meadowood articles here.