By LESLIE BISHOP, guest columnist
What animal can walk on water, sail on a windy day, go fishing and scuba dive?
Give up? Why, dolomedes triton, the six-spotted fishing spider, of course!
I am talking about one of my favorite animals to watch on a summer day. It’s a great excuse to sit by the pond and to watch and wait for action.
Six-spotted fishing spiders are easy to identify. They are large (about 2½ inches long) with a distinctive pattern. They have two white stripes on their front section (cephalothorax) and 12 white spots on their plump, greenish abdomen. They are named for the six black spots on their underside. They are common near shore in ponds and lakes and are often seen floating on the water surface.
Story continues below gallery
These spiders can walk on water using the properties of surface tension and by spreading their body weight equally where each of the eight legs contacts the water. When they move forward, they row their second and third pair of legs back, while keeping the first and fourth pairs steady to retain the surface tension. On a breezy day, fishing spiders can take advantage of wind propulsion. By lifting their two front legs, or by slightly lifting their bodies into the wind, they can sail across the pond without any effort.
I often get calls from hysterical people saying they have a monster spider in their canoe or on their dock.
Relax, I say. These spiders are not dangerous to humans. They can bite if poked and prodded, but the bite is no worse than a bee sting.
But watch out, aquatic insects, minnows and tadpoles! Fishing spiders detect their prey using vibrations on the water’s surface. Whenever a fish or tadpole comes to the surface to feed, the motion creates concentric water surface waves.
Spider legs have delicate hairs called trichobothria that respond to vibrations carried through either the air or the water. These sensory structures provide information to the spider’s nervous system about the presence and location of prey as detected from the disturbance on the water surface. The spider can accurately locate the center of these concentric circles and attack.
Similarly, fishing spiders can also use water-borne vibrations as a warning that a predator is near. Birds, bats and fish commonly attempt to eat fishing spiders that are on the water surface. When the spider detects predator vibrations from above, she or he will dive underneath the water and hide in submerged plants or sticks.
What amazes me is that the spider can stay submerged for 30 minutes or more. The hairs on their bodies trap air and provide a protective diving suit.
If the vibrations come from a fish predator, the spider can push off from the water and jump straight up to avoid the attack.
Fishing spiders are also called nursery web spiders because of their excellent maternal care. Female fishing spiders will lay eggs and wrap them in a silken sac. She will carry this sac around in her jaws for protection until the eggs are ready to hatch. Then she will construct a nursery by tying plant material into a tent with silk. She diligently guards the nursery full of her spiderlings and will attack anything that threatens the silk structure.
There is more to tell, but I have to get back outside to the pond. Discover for yourself the fascinating feats of the six-spotted fishing spider!
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She is a volunteer interpretive naturalist at Brown County State Park. She can be reached through the newspaper at email@example.com.