Fishing spiders, Dolomedes tenebrosus, are venomous, carnivorous and enormous. However, these spiders are not our enemy, and they do not eat our plants. They eat the bugs that do, as well as insects that sting and spread dreaded diseases, like mosquito larvae.
These huge, but shy, spiders fear anything larger than themselves, so we are safe in their company. Although the sight of such a spider might startle us, we should treat them with respect. Simply give them time to scamper away, or allow them to remain hidden on a tree’s bark, a rock at the water’s edge or within the green foliage.
The fishing spider and the similar wolf spider are the largest non-webbing spiders in Louisiana and are frequently mistaken for one another. They are easily camoflagued by a blackish gray and tan coloration. The wolf spider will not be found on land whereas the fishing spider is both terrestrial and aquatic. Both have long, thin, tapered legs covered with dark hair. Among the hairs on the fishing spider are sharp spines used for catching and clutching and carting away prey. The spindly legs are dark and banded, looking like the hide of a zebra.
On the front of his face are eight eyes in two curved rows of three, with two larger eyes above these. His face appears to end in grey whiskers below a dark mustache. However, you probably will not get near enough to see these facial features.
They may be found deep in the woods, prefering life in forest pools, on streams, around boat docks or in gardens near homes where they will stay under cover during the day.
They are carnivorous nighttime predators looking for aquatic insects, tadpoles, frogs or small fish. Their venom turns the victims’ insides into a soup-like substance the spider can suck out and injest. Annie Dillard, in “Pilgrim at Tinker Creek”, has written of seeing a deflated frog on the edge of a pond with a full-bellied spider walking away. They can be cannibals, eating other spiders ... even their own kind. Yes, they have the reputation of eating their mate just like the black widow does, but in this case, the male fishing spider does not suffer. Instead, he always dies immediately after mating. The female does not kill him. He is already dead before she can get to him, and his body provides her with a meal rich in protein. Dolomedes Tenebrosus Mating on youtube.com shows this behavior in a three-minute video. There are other such videos, but this one is accompanied by pleasant music. Others sound like Vincent Price’s organ music in old horror films.
To protect her eggs, she builds a web mat, lays several hundred eggs on the mat, then wraps them all into a ball. She carries this in her jaws, then secures it to a safe spot. These webbed balls of eggs are often found under rafters in boat houses or in a nest of leaves she has sewn together. These graceful spiders come into the world under the watchful eye of a cautious mother who stands guard as they grow from one molt to the next until the hatchlings are ready to float off on their own silken thread. At this point, the siblings take flight simoultaneously, like an army of tiny survalence balloons.
The adult spider not only swims and fishes under water, it also water-skis, using hair on its feet (the back pedis) to glide across the water. The spider sits back on his hind legs while holding the front legs up to catch a breeze and away it goes.
When on the water’s surface, the sensory hairs on his eight feet can detect the motion of prey. His back legs hold onto vegetation while the front legs grab its victim. While on the surface, the tension of the water is strong enough to support the slight weight of the spider, which can actually walk or even jump on water. Each foot merely creates an indentation without breaking the surface.
To stay under water the hairs on the abdomen hold air bubbles ... enough air for a fishing spider to stay as long as 30 minutes. Here, the spider hides from enemies above or stalks prey below.
Large and frightening to look at, these spiders are ecologically beneficial to Louisiana’s ponds, forests and gardens, if for no other reason than that they consume mosquito larvae. Granted, they may eat a few innocent tadpoles, but their consumption of harmful insects is well worth the price.
Remember: leave these spiders alone; look on them as your friends.
(Betsy Trammell, Louisiana tree farm forest landowner and CenLa Master Naturalist.)