The air is a-buzz with insects! Some have many generations every year - many are true flies like mosquitoes and midges, but there's some stream mayflies.
Other insects have just 1 generation in a year - like butterflies, many beetles, and most stream-dwelling caddisflies.
A few live v-e-r-y slowly - sometimes because their food isn't very nutritious. Beetles that live in decomposing wood take many years to grow from larvae to adults.
What insects have you seen lately? Where did you see them? Can you tell us how long they live?
(A handy website for identifying all kinds of invertebrates is http://bugguide.net)