Monday, December 18, 2006

Wolf and Nursery Spiders

Wolf Spiders are known for their size and named because they hunt for food rather than sit in a web waiting for it to come to them. The female is the only spider that gives parental care after the babies are hatched, by carrying them around. As you can see from this one on the steps out front, it makes her look like she's having a "bad hair day." Think of her as a "mom" and not a spider.

Spiders are invertebrates, which means they don't have backbones. They are beneficial critters since they pollinate plants, eat harmful insects, and help to recycle dead trees and animals back into the earth. They also provide a vital source of food to many birds, fish and other small mammals. Spiders are not insects which have 3 body parts and 6 legs. Spiders have 8 legs and 2 body parts. Male spiders are usually smaller than females. Most spiders are very nearsighted although they have more than one set of eyes. They use the hair on their body to sense when other animals are near. To escape predators, they may jump a distance of 5-6 inches.

Fear of spiders is called arachnophobia and it is one of the most common fears among humans. Cobwebs are made by spiders that spin silk from glands called spinnerets, located at the tip of their abdomen. Not all spiders spin webs and the Wolf Spider is an example of one that does not. Webs get dirty and torn, so many spiders spin a new one daily. They roll the old one up in a ball and eat it. All spiders require a constant source of moisture.

Most spiders sit in their webs and wait for prey to come to them, but Wolf Spiders are hunters with keen eyesight. They seek their prey and pounce on them, like wolves, often prowling in the dark. They are easily spotted because of their size which can be more than 3 inches wide with legs. They eat prey of their own size or smaller like mosquitos, roaches, ants, flies and crickets. They also get food from dead carcasses. They are able to eat a large amount of food with their flexible abdomen and can then do fairly well without food for a week or longer by decreasing their metabolism.

Courtship behavior among spiders is highly ritualized and often species specific. For those with well-developed eyes like the Wolf Spider, courtship includes movement and bright contrasting colors.
After mating, the female Wolf Spider seeks out a secluded spot where she lays 100 or more eggs, guarding them ferociously until she can encase them safely in a sac of silk she spins and then attaches to her spinnerets at the rear.

Because they are constantly on the move for food, they can't keep an eye on their egg sacs, as most spiders do with webs. She carries the sac about a month when the babies emerge having already gone through one molt in the egg sac. They climb out and on to the female's abdomen area and cling to hairs where they will ride for a week or two. The female carries about 100+ babies which provides some protection for them and also provides a way of dispersing them. This is the only spider that shows this type of parental care.

Female Nursery Spiders also carry their egg sac with them. The difference is that with Nursery Spiders, the sac is not attached to the spinnerets. It is carried around in her jaws or pedipalps (legs) like this one on the side of our porch. When the eggs are about to hatch, the female builds a nursery "tent" to put her egg sac in, and then guards it from outside.

The female Nursery Spider will sometimes eat the male after mating. The male, to reduce the risk of this, often presents the female with a gift such as a fly, when approaching, in the hope that this will satisfy her hunger.

No comments:

Share This Post