Midges are small flies that belong to several families of non-mosquito Nematoceran Diptera. They are found on practically every land area outside permanently arid deserts and the frigid zones. Some midges, such as many Phlebotominae and Simuliidae, are vectors of various diseases, while many others play useful roles as prey for insectivores, such as various frogs and swallows, and as detritivores, forming part of various nutrient cycles. Midges are actually many different species of tiny flies, and not all species bite, but like mosquitoes, the females of some species need blood to reproduce. Their bites can cause irritation and swelling, and some species are known as "no-see-ums" because they are so small and hard to see. Midges are often called "bloodworms" as larvae, for they are red from the hemoglobin molecules within their narrow bodies. They live at the bottom of lakes, ponds, and other aquatic habitats and often construct tubes from fine sediment and mucus. Adult midges, unlike mosquitoes, typically have a short proboscis and do not bite people. Midges are found in practically every environment on earth, except the permanent cold deserts of the poles and the permanent hot deserts of arid zones. They are a major food source for fish, birds, and insects.