You could make the body out of chocolate and use those noodles you use at christmas time to make the haystacks with. I'm not sure what there called but they come in a can. I think they might be chinese noodles.
Or you could use a nutterbutter cookie dip in chocolate and make fondant legs. HTH
You could also use thin licorice rope for the legs, embedded in the body which could be fondant or chocolate colored black.
here is a spider recipe:
For spider, place one gumdrop in center of web design on top of cupcake. Roll out another gumdrop with rolling pin on generously sugared surface. Slice thinly and roll into "legs." Arrange legs around gumdrop to complete spider. Repeat with remaining gumdrops and cupcakes.
found here: http://recipes.howstuffworks.com/spider-cupcakes-recipe.htm
I would do chocolate candy clay with the chocolate covered Chinese noodles MeeMaw was talking about. They'd have the right shape then, and not everyone likes black licorice.
Or royal icing!!! I have this page...Let me find it and I'll post the link...
There you go.
OK I know it's icing, but seriously, that picture gave me the heebie jeebies.
i second what "ceshell" said..... scary... super scared of spiders. when i was a lil girl and was drying my hair, and bent over to wrap my hair in the towel and then stood up straight, a spider had been in the towel and it was crawling down my face. ever since then, MAJOR FEAR OF SPIDERS