|Fishing Spider - Dolomedes tenebrosus|
Family Pisauridae. Live adult spider photographed at Waterfall Glen Forest Preserve, DuPage County Illinois, at Sawmill Creek. Size: 60mm (almost 2½ inches) from tips of back legs to tips of front legs.
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The semi-aquatic fishing or "raft" spiders of Europe and North America are quite large. The females can reach a body length of 30mm (over 1 inch). They hunt on the surface of still or slow-moving fresh water. They row themselves across the surface much like pond skaters, supported by the surface tension, and can also sail across on the wind.
Their legs are higly sensitive to vibrations sent out by floating insects, especially those in distress. The spider will rapidly approach the prey, inject it with venom, then drag the unfortunate to shore, where it can be consumed without danger from other (underwater) predators. They have also been known to dangle a leg under the water surface in order to attract small fish, which they then capture by making a sudden plunge, holding the fish in the powerful legs while subduing it with venom. Fish are also dragged bodily to bankside to be consumed.
Class Arachnida / Order Araneae: Spiders are the largest group of arachnids. They are easily recognized by their eight legs, and there are few creatures great or small that elicit such irrational fear in mankind. The vast majority of spiders are completely harmless and offer beneficial services, chief of which is keeping the burgeoning insect population in check. I am continually amazed at the resourcefulness of these supremely successful predators.
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