Black widows
If the red mark is in the shape of an hourglass, and on the underside of the abdomen (not on the top), it might be a Brown Widow Spider. However, Brown Widows only live in certain areas, so it really depends on where you live.
trarantrala
a red back looks almost the same. But doesnt have an hourglass shape. It has a red stripe on top of its abdomen.
A black widow. This spider is only a black widow if the entire spider is black, with a round-ball looking back-body, female variety if there is a red hourglass shape marking on the underside of the spider. From the top black widows are completely black.
The top is shiny black. Some have a red hourglass on the underside, some are solid black. See the Related Link for pictures of black widow spiders.
The Spider's body has two parts: a fused head and thorax (cephalothorax or prosoma), and the abdomen or opisthosoma (the rear body). The heart is located at the top-front of the abdomen.
Closely related. Black widow has an hour glass red mark underneath its abdomen while the red back has a red mark (not hourglass) on top of its abdomen.
It sounds like the famous black widow spider. they can be poisonous but if you avoid them at all costs they wont bother you, they only bite if you poke at them and go near and annoy them !!
There are a number of black spiders with red on their backs. The most commonly referenced one is probably the black widow. But it is not the only one, and not all of them have red on their backs.It might help to note that the female black widow is mostly black, and may or may not have red (or red-to-orange color) on its "back" or the top sIde of its abdomen. (Viewed from the top or above, the female black widow is all or almost all black.) Some have a splash of red on their "back" or the top of their abdomen. Additionally, the hourglass that appears on the female L. mactans varies a bit from red to orange, and can be very dark in color. This characteristic mark is always on the bottom or ventral side of its abdomen.
The red canary charlie spider
Yes. Ventral can mean closer to the abdomen, below or the bottom surface of an object such as ventral surface of the tongue (bottom side).
the top side is normally brighter with semi-visible veins. the underside is normally darker with very visible veins.