A Black Widow.
it could be the red back spider but that depends on where you are hope that helps
A short, squat black spider that jumps and has a red spot on its back is probably a red-backed jumping spider. These are common in the Pacific Northwest, including Vancouver Island.
It's probably a black widow and yes very poisonous.
A black widow is a spider with a red mark on its 'back'
Black and red spider
This has to be the yellow and black red spotted spider.
A green spider with a red spot is dangerous if it is a red back. Normally, green spiders are not dangerous.
It may be a Black Widow spider. They are very poisonous and it is probably best not to approach it if you are unsure of the species. Black spiders have a distinctive red "hourglass" shape on its back.
i saw the same spider. it is freaking me out. it is bright green with a red spot on its black. i cannot find a picture of it. what is it?
It could be a black widow spider if it is small and thin-legged with a shiny round black abdomen and red markings under it. If it's fuzzy with a red spot on it's back, and the front part of the body is more-or-less the same size as back part, then it's a black jumping spider.
The spider that is black with a white crescent on its back is the Brown House Spider. This spider is often confused with the red-back spider.