Wolf Spiders

Araneae

by Jay W. Sharp

Hairy as Bigfoot, swift as a barracuda and nearly the size of a tarantula, the wolf spider, like other hunting spiders, may ambush or run down its prey, which includes insects such as earwigs, ants, beetles, grasshoppers, crickets, roaches and other spiders. It took its name from folklore, which suggested that it hunted in packs, like wolves. They are, in fact, solitary hunters, in spite of their name.

Like the brethren within its order (called Araneae), the wolf spider has two body segments: a fused head and thorax and an unsegmented abdomen. Its fused head and thorax include its central nervous system, eyes, fang-like mouthparts and venom glands. Its abdomen holds its heart, breathing organs, digestive system and, at the tip, several silk-producing spinnerets. Its eight long jointed legs – equipped with sensitive hairs that help detect air disturbances by potential prey or predators – connect to its head and thorax. The male has, attached just behind the mouthparts, two additional appendages, called palps, which it uses in holding and positioning prey and in the mating ritual. While some species weave their silk into distinctively designed webs for ensnaring and holding prey, the wolf spider uses its silk to line its shelter and fabricate its egg sac.

 

 

The generally hairy and robust wolf spider species of the Southwestern deserts range from perhaps half an inch to a couple of inches in body length. Typically, they vary from black to brown to gray in color, sometimes with a pattern along the back of the abdomen and head and thorax and sometimes with an orangish coloration on the face. It has excellent camouflage for a life on the pebbled and sandy surface of the desert floor. According to the Spider Bites website, the wolf spider, like most Araneae, has eight “simple” eyes—organs that can detect light and darkness. Characteristically, the wolf spider’s eyes occur in three horizontal rows, with four small eyes in the bottom row, two large eyes in the middle row, and two medium-sized eyes in the top row.

 

Eerily, “their green eye shine can be easily seen as they cross roads at night,” according to Arizona-Sonora Desert Museum website. “The eye shine is caused by a tapetum [a membranous layer] in the eye which reflects light rays back through the eye retina and probably enhances the spider’s night vision.”

If touched or threatened, the wolf spider will bite, causing “pain, redness and swelling,” says the California Poison Action Line website. “The large jaws/fangs can cause a tear in the skin as they bite. Swollen lymph glands may develop. The skin area at the bite may turn black. Swelling and pain can last up to ten days.” Nevertheless, its bite is not considered lethal for humans.

Range, Habitat and Home

The wolf spider, comprising more than 2000 species worldwide and well over 100 species in the United States, occupies a diversity of environments, ranging from desert scrublands and riverbanks to swamplands to rocky coastal areas to grasslands to mountain forests. A single species’ range may span a large region. For instance, the species Schizocosa mccooki has a range that extends from southern Canada and Michigan across central Texas and the Southwest into central Mexico and to the Pacific coast, according to an article written by Gail E. Stratton and Donald C. Lowrie for a 1984 edition of The Journal of Arachnology.

In the desert, the ground-dwelling wolf spider, faced with daytime soil temperatures as high as 150 degrees Fahrenheit or more, stakes out a home territory that offers protection from the heat, the highest availability of humidity, a sufficient abundance of prey, and a presence of potential mates. At least some species appear to favor riverine environments, with the less extreme temperatures and the more diverse and abundant prey. Territories may vary from a few square feet to several hundred square feet.

Primarily a nighttime hunter in the desert, the wolf spider may take shelter from the daytime heat and from predators by appropriating abandoned rodent or reptile burrows, occupying rock alcoves, or excavating its own burrow.

A wolf spider [probably a female] that constructs its own burrow spins “a circular-shaped flooring on the ground,” said Roland S. Shook in an article in a 1978 edition of The Journal of Arachnology. The spider then “digs up this mat and moves it to one side with the sand sticking to it. This procedure is repeated until the burrow is dug to the proper depth. The burrow is as big as the spider but enlargements in the diameter of the burrow are made at various levels to allow the spider to turn around.” Next, the wolf spider – an eight-legged architect – may construct a turret surrounding its burrow entrance, using grass, mud and small twigs. Finally, it spins a seamless silk lining for the burrow and turret. The spider may build the turret to deflect water runoff or blowing dirt or to signal potential intrusions.

Courtship and Mating

A male wolf spider, usually amorous during the summer months, approaches a female with caution. Intuitively, he knows that, with her eight simple eyes, she can see no more of him than light and shadow. Moreover, he is the smaller of the two. He waves his front legs and his palps to identify himself and signal his intentions. Otherwise, he may wind up, not as her mate, but as her prey.

Stratton and Lowrie said that in their studies of the species Schizocosa mccooki, the male started the courtship with a “quick jump.” He then began a papal drumming, which biologists sometimes call “bursts of percussion” or “stridulatory sounds,” communicating his lustful desires to the female. “In some instances,” said Patton, “the palps were raised and lowered together, but usually the palps were drummed in an alternating sequence.” Just like a human drummer, it seems.

The male – if his rhythmic serenade wins her affection – mounts the female. He may expect better luck if he is previously known to the female. “With his head facing her hind part,” says the Lady Wildlife website, “he inserts each palp alternately into her genital opening. During mating the female often continues to move around and catch prey with the male on her back.” He does not seem to think that her casualness compromises the passion of their relationship.

Care of the Young

After mating, possibly for the second time over the course of a summer, the female wolf spider seeks out a secluded spot, where she lays perhaps 100 or more eggs, guarding them ferociously until she can encase them safely in a sac of silk. For the next several days to several weeks, depending on the species, she will carry the egg sac attached to her abdomen. If she has constructed a burrow, she may sit at the turret, with her head in the opening and her abdomen and the eggs in the sunlight during the warmer part of a summer day. She may be “sunning” the eggs to accelerate their development, according to Shook, or she could be shielding them from a fungus that may infect them in the higher humidity deeper in the burrow.

When the time comes for hatching, she rips open the egg sac, releasing her offspring. They immediately swarm over her, covering her body and legs. They cling to her for several days before they drop to the ground, ready to begin their independent lives.

Wolf Spider with babies on abdomen

Some of her spiderlings – lighter than a wisp of smoke – may climb to the top of a plant, discharge strands from its spinnerets, creating a silken “balloon.” They ascend to the sky when the breath of the wind lifts their balloon, sometimes traveling for miles to a new home.

As a young wolf spider grows, it produces a new exoskeleton, underneath its old one. It then molts, shedding the old exoskeleton, crawling out of it like an acrobat shedding tights. When it reaches sexual maturity – a process that may take some months – it will no longer molt.

Eat and Be Eaten

Whether the wolf spider ambushes or runs down its prey, it uses its legs to seize and its jaws to hold and crush its victim. It uses it fang-like mouthparts to inject venom, starting the process of digestion. It feeds on its victim’s juices. It is “very reluctant to relinquish” its prey, said Shook. It may leave a small pellet of its prey’s remains after it is done eating. Other times, said Jennifer L. Maupin and Susan E. Riechert in an article in the 2001 edition of Behavioral Ecology, the wolf spider may eat only part of its kill or it may abandon the kill altogether, a practice called “superfluous killing.” In its immediate range, where numerous neighbors may occupy evenly distributed burrows, none with overlapping territories, the wolf spider may help control the populations of various prey species.

While the wolf spider preys on numerous species, it may also become the prey of various other species, for instance, coyotes, screech owls, elf owls and various predatory insects, including a predatory wasp, according to Shook. The wolf spider, if caught by the wasp, will be stung into paralysis. It will be deposited in a safe retreat by the wasp, which will lay an egg (or several eggs) on the moribund body. It will be eaten alive by the wasp’s larvae.

In a struggle with a predator, a wolf spider may sacrifice a leg to escape. “This behavior is immediately beneficial, since it allows escape from otherwise certain death, but may have long-term consequences,” says biologist Dr. Chris Brown, Research in the Brown Lab Internet site. A wolf spider with a missing leg moves more slowly, compromising its ability to capture prey or escape predation.

Seasonality and Life Span

The wolf spider mates, reproduces and hunts primarily from late spring to early fall, not hibernating but becoming torpid (as least in the case of the Schizocosa mccooki) during the colder winter days in the desert.

The male wolf spider probably dies in the summer of its maturity, following its first mating. The female may live for another year after her first brood.

Desert Animals & Wildlife
Black Widow Spiders
Brown Recluse Spider
Tarantulas

 

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