The term 'small fly' can refer to two different species of insects, the MIDGE and the GNAT. The MIDGE is a small, two-winged fly that is usually found near water sources and is typically less than 5 millimeters in length. The GNAT is also a small, two-winged fly, but it is usually found in more arid environments and is typically less than 3 millimeters in length. Both species are considered pests due to their ability to spread disease and contaminate food sources.