Dark Fishing Spider

Dolomedes tenebrosus — the dark fishing spider — is one of about 100 species in genus Dolomedes (the fishing spiders — large semi-aquatic spiders that hunt on water surface) and one of the largest spiders commonly encountered in eastern NA homes. The species is widespread across all of eastern North America from southern Canada south through the eastern US to northern Florida. Adults are 15-25 mm body length (females larger than males) with leg span reaching 7-9 cm — large enough to fully cover the human palm. The species' diagnostic features: brown-and-black body with intricate camouflage markings (W-or-V-shaped pattern on the dorsal abdomen, banded legs), large prominent eyes (eight eyes typical of spiders, with the front pair often appearing especially prominent), and the relatively flat-and-spread leg posture characteristic of the Pisauridae and Lycosidae (compared to the more compact body posture of orb-weaving spiders). Despite the family name 'fishing spider' (genus Dolomedes is famous for the spider species that hunt on water surface — running across pond surfaces, diving underwater, capturing small fish and tadpoles — see Dolomedes triton, the six-spotted fishing spider, and other aquatic Dolomedes), the DARK FISHING SPIDER IS MORE TERRESTRIAL than its aquatic relatives. Dark fishing spiders typically hunt on tree trunks, in woodland leaf litter, around rocks, and in shaded outdoor structures — though they will swim and dive if pushed into water. The species is famous in eastern NA for HOUSE INVASION behavior, especially in LATE SUMMER (August-October) when adult males disperse from natal territories to find females. House invasion sees dark fishing spiders entering through gaps under doors, around windows, and in basements — appearing dramatically large and intimidating to homeowners despite the lack of medical risk. The dramatic size makes the species one of the most-Googled and most-screamed-about house spiders in eastern NA. The species is essentially HARMLESS TO HUMANS — bites are extremely rare (the species is not aggressive and prefers escape over confrontation), and the venom is not medically significant (causes only minor local irritation similar to a mild bee sting). Like the related nursery web spider (already in the Wild Files), female dark fishing spiders carry their EGG SACS attached to the chelicerae (rather than to the spinnerets like wolf spiders) and construct large nursery webs of silk in vegetation that contain hatching spiderlings until they molt and disperse. The species is one of the most-photographed large spiders in eastern NA macro nature photography because of the dramatic size and intricate camouflage patterns.