Wolf Spiders - Family Lycosidae
 There are over 200 species of Lycosidae in North America, ranging in size from 3 - 35mm.
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Live adult spiders photographed at various North American locations.
Wolf spiders are members of the family Lycosidae, from the Greek word "lycosa" meaning "wolf". Their namesake, their method of hunting is to run down their prey. They are robust and agile hunters that rely on good eyesight.

There are over 200 species of Lycosidae in North America, ranging in size from 3 - 35mm. They have eight eyes arranged in three rows. The bottom row consists of four small eyes, the middle row has two very large eyes (which distinguishes them from the Pisauridae), and the top row has two medium-sized eyes that face the side.

Female Wolf Spider Carries her egg sac by her spinneretes
Female Wolf Spider Carries her egg sac by her spinnerets
Wolf spiders carry their eggs along with them in a round silken globe, or egg sac, which they attach to the spinnerets at the end of their abdomen. The abdomen is held in a raised position to keep the egg case from dragging on the ground, but they are still capable of hunting while so encumbered. Also unique among spiders is their method of hatchling care: after the eggs hatch and emerge from the protective silken case, the new spiders climb up their mother's legs and crowd onto her abdomen. She may carry them around for several hours or days until they are ready to fend for themselves. It must be noted, however, that the hatchlings will scatter immediately if the mother spider is threatened or attacked.
External Spider Anatomy
External Spider Anatomy
A. Dorsal (top) view       B. Front view of face and chelicerae      C. Ventral (bottom) view (some legs omitted) [1]
Spiders, like most other arachnids, have their body divided into two portions, the cephalothorax and the abdomen. The cephalothorax consists of the head and thorax fused together. Most spiders have four pairs of legs attached here, activated by muscles inside the chitinous exoskeleton. The top of the cephalothorax is covered by a convex hardened shield (carapace), with the eyes mounted at the front.

The eyes are simple, and resemble the ocelli of insects. Most spiders have 8 eyes; Some lineages have lost some or all their eyes, ergo there are spiders with 8,6,4,2, or one or none. The size and positions of the eyes is widely variable. Many of the hunting spiders, e.g. Salticidae (jumping spiders) and Lycosidae (wolf spiders) have large, forward-facing eyes and keen vision required for their craft; many of these spiders have at the back of the eye a reflective membrane called a tapetum [1]. It is this surface that aids in night vision and causes their eyes to reflect light and shine in the dark, like a cat's eyes. Most sedentary spiders have relied on their sense of touch for so long their vision is thought to be poor [3].

Spider eye arrangements are a simple diagnostic tool that can often get you to the family level. There is a great reference at Bugguide.net showing templates for many different families [2].

Early Spring Wolf Female
Early Spring Wolf Female

Wolf Spider with hatchlings aboard
Female Wolf Spider with hatchlings aboard.

References
  1. William J. Gertsch, PhD. "American Spiders"
  2. Lynette Schimming, Bugguide.net, "Spider Eye Arrangements"
  3. Misdiagnosis of Spider Bites: Bacterial Associates, Mechanical Pathogen Transfer, and Hemolytic Potential of Venom from the Hobo Spider, Tegenaria agrestis (Araneae: Agelenidae)
    Melissa M. Gaver-Wainwright, Richard S. Zack, Matthew J. Foradori, and Laura Corley Lavine
    Journal of Medical Entomology 2011 48 (2), 382-388
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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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