Houseflies only live for 24 hours
The old claim turned out to be wrong and was rejected by evidence.
TaughtA housefly lives for a single day. Try to feel sympathy for it.
NowHouseflies live around 15 to 30 days as adults. The one-day lifespan belongs to mayflies, and even they spend most of a year as aquatic nymphs first.
What actually happened
The confusion is a swap. Adult mayflies, order Ephemeroptera, genuinely do live a day or less, and some species survive only a few minutes. They emerge without functioning mouthparts because eating is not on the schedule.
Houseflies are ordinary insects with an ordinary life cycle: egg, larva, pupa, adult, with the adult stage lasting two to four weeks in typical conditions. In that time a single female can lay 500 eggs. And the mayfly's brief adulthood is itself misleading. It spends most of its life, often close to a year, as a nymph in the streambed. The famous 24 hours is the last chapter, not the book.
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Sources
- Encyclopaedia Britannica: Houseflybritannica.com
- Encyclopaedia Britannica: Mayflybritannica.com
Who was taught this
Still standard through 2010, so anyone who finished school between 1950 and 1995 learned the earlier version.