Chullin 58 - Can Terefah Live?
There was a man in Einbul whose skull was missing a piece as large as a drill hole, but they fashioned for him a piece of dried gourd shell and he lived. Rabbi Shimon ben Elazar said, "That's no proof! It occurred in the summertime, but once the cold season came upon him, he died" - because in Rabbi Shimon's view a terefah cannot survive for more than a year. The final law is that once an animal survived for twelve months, it is not a terefah. Also, if it is a female and gave birth, it is not a terefah.
No worm can survive for more than twelve months. Therefore, dates stored in a container for that long are permitted to be eaten, since earth-produced worms disappeared, and new worms are not forbidden until they emerge from the fruit.
Incidentally, gnats don't live for more than a day. Then what about a popular saying, "For seven years the female gnat kept aloof from the male gnat, because she said to him, 'You saw a fat inhabitant of Mechozah who went swimming in the water and you sucked blood without telling me!'" - They are talking in gnat-years.
Art: Frans Hals - Boy With A Skull