Fishing spiders, belonging to the genus Dolomedes, are large, semi-aquatic spiders known for their hunting prowess. While all spiders in this genus are called "fishing spiders," the dark fishing spider (Dolomedes tenebrosus) is a particularly fascinating species, often evoking alarm due to its large size. This article delves into the diet of the dark fishing spider, exploring its hunting techniques, prey preferences, and ecological role.
Identification and Habitat
The dark fishing spider is one of the largest spiders in Maryland, vying with wolf spiders for the title. Females can have bodies up to an inch long, with a leg span exceeding three inches, approximately the size of an index finger. Males are typically half the size of females. These spiders are mottled black and brown, providing excellent camouflage in their environment, with few white markings. The abdomen features dark W-shaped patterns on the upper surface, and the legs are often banded with brown and a darker color.
Unlike web-building spiders, the dark fishing spider is often found resting upside down or vertically on wood or stone surfaces. While other fishing spiders are typically found near water, the dark fishing spider can be found in drier wooded areas, around rocks, shrubs, and other vegetation near permanent water sources. They inhabit half of the continent, from the Dakotas to Texas to the Atlantic, and up into southeastern Canada. Within that range they are often found near water, but they also stray far from it, commonly living on trees in woodlands and sometimes gaining access to basements.
Hunting Techniques
Dark fishing spiders are skilled predators that employ a variety of hunting techniques to capture their prey. They are masters at standing patiently still, a crucial skill for a spider that fishes. Their good eyesight and fine hairs on their legs, which feel ripples as insects land on or fall into the water, are adaptations that allow them to eat up to five times their weight a day. They seem able to locate downed insects based on the water’s movement.
A fishing spider perches at the dock or waterside with her front two legs dangling in the water, and her body and other six legs firmly planted on land or dock, waiting to feel ripples that signal that a mayfly, waterstrider, or other unlucky insect is briefly trapped or simply walking by. Fishing spiders walk on water, using three gaits to do so. When the tip of each leg touches the water, it creates a small indentation or dimple. Having spread her weight over these tips, she doesn’t break the surface tension of the water and thus doesn’t sink. Using her third gait, she can run surprisingly fast. Fishing spiders can dive deep enough to catch tadpoles or very small fish who’ve seen the “bait” of dangling legs.
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Like other running spiders, the dark fishing spider simply pounces on its prey and bites it. The scientific name for this species, tenebrosus, is from the Latin word for “dark” or “gloomy,” because there are so few light markings on this overall dark brown animal.
Prey Preferences
The diet of the dark fishing spider is diverse, reflecting its adaptability to different habitats. Primarily, they feed on insects and other small arthropods. Near water, their prey includes aquatic insects, tadpoles, and even small fish. They use vibrations produced when the prey traverses the surface film to locate them. Woodland-dwelling fishing spiders feed on invertebrates, even slugs, and can tackle cricket-sized prey. There have been reports of dark fishing spiders preying on crayfish and small spring peepers.
Ecological Role
Fishing spiders play a significant role in their ecosystems as predators of insects and other small creatures. They help control populations of various invertebrates, contributing to the overall balance of their habitats. To their prey, spiders are fierce predators, but being small themselves, they are also preyed upon by many other animals, such as reptiles and amphibians, birds, and mammals. Like all spiders, they are part of the delicate balancing act in nature.
Life Cycle and Maternal Care
The life cycle of fishing spiders begins with the female laying eggs and wrapping them in a silk sac. She carries the sac with her until the spiderlings hatch. The female prepares a shelter for her egg sac, which can hold 1,000-plus eggs, concealing it when it’s about time for the eggs to hatch so that the spiderlings will have shelter after they emerge. Egg sacs hatch in mid-summer; partially-grown spiderlings overwinter under loose bark, in rock piles, tree holes, etc. Nursery web spiders carry their egg case up front, in their jaws, and so cannot feed for the duration.
Researchers discovered that female Dark fishing spiders are so inclined, but his becoming a snack isn’t because he doesn’t absent himself quickly enough, after the fact. For him, mating is physiologically lethal - he dies spontaneously. He doesn’t go to waste, though, and his contribution ensures the continuation of his genes. A female may re-mate, but a male will pay more attention to virgin females (he can tell by the scent of the silk she lays down).
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Interaction with Humans
Despite their large size, fishing spiders are not considered dangerous to humans. Their venom is not toxic to humans, and they are quite shy. They eat a great variety of insects, and most knowledgeable gardeners welcome them into their gardens. While fishing spiders may not live in a garden, they do their share of insect eating.
To prevent fishing spiders from entering homes, it is important to maintain a dry environment in and around the house. Fix leaks promptly, ensure effective drainage around your home, and use dehumidifiers in damp areas like basements. Regularly inspect and seal entry points.
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