An entamologist would have to see it to give you an id. Part of it is counting it's eyes.
The spider with a big white butt is likely a species of orb-weaver spider, known for their distinctive white or light-colored abdomens.
a redback spider
The spider you are describing is likely the black widow spider. It is known for its shiny black body with a red hourglass-shaped marking on its abdomen. This spider is venomous and can be found in various parts of the world.
Your mom.
THE ONE WITH MIXED PARENTS
I think its a white tail :D
If its black, has a large butt and there's a red shape on its back the resembles an hourglass, then its a black widow spider and they are very poisonous
Don't mind if I do. (Yum.)
I'm trying to figure this out too, today my daughter came screaming out of her room she told me there was a black spider with white stripes on its butt and she wasn't going to go back into her room until i killed it........ You'll have to do a bit more research. If web is spread out and symmetrical, sounds like an orb weaver of some sort. If it's a funnel, then could be a funnel spider. Mine turns out to be a grass spider (more to the name up front, but don't recall). flat web with funnel at end. Just remember, most spiders are helpful. Granted - all of these are rather big and "substantial" looking - but mine turns out harmless. Good luck!
I believe it is a type of jeweled spider.
Based on your description, the spider you are most likely referring to is the white-marked jumping spider (Dendryphantes varians). This species is commonly found in Pennsylvania and is known for the distinctive white heart-shaped marking on its back. White-marked jumping spiders are harmless and are beneficial for controlling pest insects in gardens.
Identifying spiders is difficult to do without knowing more than just the spider's color.. Body type, the presence or absence of hair, and where the spider is found can all help to make a positive identification. A spider with a black body and brown legs is likely to be a common house spider, which is not dangerous.