These long-legged, dark-colored spiders are set apart from their arachnid cousins by their unique hunting method – they can dive underwater in search of aquatic prey. Though the venom of these spiders is toxic enough to kill a tiny minnow, their bites do not pose a dire threat to humans.
Species: Six-spotted fishing spider
Scientific name: Dolomedes triton
Claim to fame: These long-legged, dark-colored spiders are set apart from their arachnid cousins by their unique hunting method – they can dive underwater in search of aquatic prey. Though the venom of these spiders is toxic enough to kill a tiny minnow, their bites do not pose a dire threat to humans. As is the case with most spiders, they would rather hide from humans than bite them. However, they will bite if cornered and provoked. Though this bite isn’t fatal, it still may hurt so it’s better to observe fishing spiders than try to catch them.
Species status: It’s presumed fishing spider numbers in Missouri are stable.
First discovered: The first scientific description of fishing spiders, in general, was written by the French entomologist Pierre Andre Latreille in 1804. The first description of the six-spotted fishing spider was written by the French naturalist Charles Athanasie Walckenaer in 1837.
Family matters: Six-spotted fishing spiders belong to the arachnid family Pisauridae, a group of species known as the nursery web spiders. Within this group, six-spotted fishing spiders are members of the Dolomedes genus. Many of the 99 species in this genus (nine of which live in North America) reside in semi-aquatic habitats.
Length: Females can exceed 30 millimeters, males usually measure up to 26 millimeters.
Diet: This spider feeds on insect larvae, aquatic insects, tadpoles and small fish. It can eat up to five times its own weight in a single day.
Weight: Less than one ounce
Distinguishing characteristics: An identifying characteristic of this spider is that its oval abdomen is smaller than its broad, rounded cephalothorax. It has a whitish-yellow rim stripe that surrounds its dark carapace and sometimes its abdomen. On top of its abdomen are three distinctive pairs of small white spots. Its dark-brown legs are thick and dotted with white hairs. As stated above, one of its most unique traits is its aquatic hunting method. This spider is diurnal (active during the day) and does not spin a web. Web-spinning spiders rely on vibrations on their web more than vision to lead them to prey. Fishing spiders have better vision than their web-spinning cousins and use it to watch for concentric surface waves and, more importantly, the prey that causes them. The spider encases itself in an air bubble and dives in pursuit of its prey and can stay underwater for several minutes. Since ripples in water can be caused by a number of things (falling twigs, falling seeds, etc.), studies have shown that many of a fishing spider’s dives are in pursuit of false alarms. Some studies estimate a fishing spider finds food on approximately nine percent of its dives. Sometimes it has been observed dabbling its front legs in water in an effort to attract prey. Fishing spiders can also run across water, much as a water strider can.
Life span: In Missouri, most fishing spiders probably live for one year.
Habitat: Six-spotted fishing spiders prefer ponds, swamps and the slow-moving, shallow areas of streams or lakes.
Life cycle: Males have to court and mate females cautiously, lest they get eaten by the opposite sex. After mating and egg fertilization, females spin a silk sack to contain the eggs and carry this sac in their front jaws until just before the eggs hatch. At this time, the female will place her egg sac between leaves in a shelter made especially for this occasion. The female guards her eggs and the resulting offspring until the young are ready to be on their own – which is usually about a week after they hatch.