1 MayfliesMayflies secures top position on this list. Mayflies survive for only 24 hours and earns them the name of ‘one-day insects’ because of their shortest life span. There are 2500 different species of mayflies in the world. In fact, some members of mayfly family die within few hours. Mayflies spend most of their lifetime as nymphs. Mayflies are important source of food for the trout, bass, catfish, frogs, nests and birds.
2 GastrotrichsGastrotrichs ranks second in this list with a life circle of only 3 days. Gastrotrichs are one of marine microorganisms with a transparent body and they usually swim along the direction of the water currents. Gastrotrichs can reach 3 mm in length. They have both male and female organs for reproduction.