Earlier in the summer, you may have glimpsed a spider carrying its white egg sac around with it, clasping it with the spinnerets at the end of its abdomen. When the spiderlings hatch they crawl up their mother’s legs onto her abdomen, latch onto special knob-shaped hairs, and ride around with her for several weeks (see inset). Only wolf spiders carry their egg sacs and offspring in this manner.
After molting, which occurs mid-summer, the young spiders disperse. Eventually the mother is free to hunt for prey without the encumbrance of hitch-hiking offspring. If you look closely at the pictured wolf spider, you may be able to make out the last lingering spiderling located at the junction of the wolf spider’s cephalothorax and abdomen.
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Just a few days ago, this adult female wolf spider’s abdomen was covered three-spiders-deep with newborn wolf spiderlings. Wolf spiders, unlike most spiders, do not abandon their eggs. They carry their egg sac around with them until the eggs hatch, grasping it with spinnerets located at the tip of their abdomen. Not only does the female not desert her eggs, but she also provides protection for her newborn spiders. After hatching, the several dozen or more young crawl up onto her abdomen, where they ride around for several days. Eventually they drop off and begin a life of their own. In this photo, only three spiderlings remain (look closely) and they abandoned ship within the hour.
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Wolf spiders and nursery web spiders look a lot alike. One way to tell one from the other is to look at the arrangement of the spider’s eyes. Nursery web spiders (family Pisauridae) have two rows of four eyes each, all roughly the same size. Wolf spiders (family Lycosidae) have a row of four small eyes, above which there are two large eyes, with two very small eyes a short distance behind them. From looking at the eyes of the pictured spider, one would assume it was a wolf spider (smallest, topmost eyes are not visible).
However, a second way to distinguish these two families of spiders is to notice how the females carry their egg sacs (the females of both species carry their egg sacs with them wherever they go). Wolf spiders attach their egg sacs to the spinnerets located at the tip of their abdomen, whereas nursery web spiders carry them in their pedipalps (two appendages that look like, but aren’t, legs ) and mouthparts, as seen in this photo.
Thus, this particular spider has wolf spider eye arrangement, and practices a nursery web spider egg sac-carrying technique. My assumption is that this is a mixed up wolf spider or one with tired spinnerets.
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Spinnerets, located at the far end of a spider’s abdomen, serve as spigots through which silk is exuded, but they also have another function for some species of arachnids. Female wolf spiders use their spinnerets to grasp their eggs sacs, enabling them to carry and guard their eggs until they hatch. In order not to damage the eggs when she moves, the spider tilts her abdomen up slightly. Catching prey with this added encumbrance and in this position must take great skill. Once the wolf spider’s eggs hatch, the young climb up on top of the abdomen where they spend their first days before dispersing. (Nursery web spiders also carry their egg sacs with them, but clasp them with their jaws, or chelicerae, and small, leg-like appendages called pedipalps.)
Wolf spiders can already be seen scurrying around fields, active after a long winter’s nap deep inside tussocks of grass where they stay until the temperature begins to rise. Some are tiny and black, while others, such as the pictured wolf spider, are larger (1 ½”) and a shade of brown. These spiders hibernate in the winter, but other species have different survival strategies. Some, like the black-and-yellow argiope, or garden spider, only live one season and die during late fall or winter, leaving behind their egg sac for next season. Many of the more active species that hunt prey rather than trap it in a web, spend the winter as nymphs, or juveniles, becoming full grown in the spring or early summer. In several species of spiders, young spiderlings hatch out in the fall and then remain in a communal egg sac through the winter.
Female wolf spiders provide both their eggs and young with a considerable amount of maternal care. They actually carry their egg sac around with them, attached to the spinnerets at the end of their abdomen, as they hunt for food and go about their lives. Careful to keep her egg sac from touching the ground, the mother makes sure it receives a sufficient amount of sunlight each day, presumably to enhance incubation. She also mends any tears that appear in the sac. The eggs hatch in one to two weeks, and 4 to 22 days later, the mother perforates the egg sac either part way or all the way around the seam by rotating the sac with her legs as she makes tiny holes in it with her chelicerae (mouthparts). Within three hours of this, spiderlings crawl out of the sac through the holes made by the mother, climb up onto her abdomen (see photo), and remain there for days or weeks, depending on the species.