No, male mosquitoes live on plant juices, sugary saps, and liquids from decomposition. They do not have a biting mouth that can penetrate human skin, but female mosquitoes do. In some species, the females, who lay as many as 200 eggs, need blood to lay their eggs—which leads to those painful bites that make humans and other animals itch.
Black Widow spiders are easily distinguished by the bright-red hourglass marking on their abdomens. Their bite is venomous and very painful, although not usually lethal for healthy adults. Nevertheless, if you are bitten, obtain treatment as soon as possible.