Fleas are parasites that feed on humans and other warm blooded animals. When you have a flea problem you and your pets serve as the host. Most of the time, fleas prefer nonhuman source for feeding, but if infestations are heavy, or when other hosts are not available, fleas will feed on humans. Fleas usually require warm and humid conditions to develop. A flea can jump 7 to 8 inches vertically and 14 to 16 inches horizontally with their long and powerful legs. A skin reaction to a flea bite appears as a slightly raised and red itchy spot. Sometimes these sores bleed.