system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do May Flies exist if they only live for 24 hours and are only around for about a month out of the year? What happens to them for the rest of the year?
gpt
What you see are adult, sexually active mayflies. The nymph stage (juvenile stage) live underwater for upwards of years before rising to the surface and molting into the subimago stage (adult stage), which then molt again into the imago stage (sexually active stage) within a few minutes to a few days depending on the specific species.  


It is only during the last two stages that we generally encounter them, but rest assured they're happily swimming away underwater all year round.