The 4 stages at 25 °C: egg about 1 day, larva about 4 days (three instars), pupa about 4.1 days, then adult. Egg to adult: about 9 days at 25 °C, 11 at 22 °C and 19 at 18 °C (Bloomington Drosophila Stock Center). Adults start laying 1–2 days after emerging, so a new generation begins every 10–11 days.
Life cycle: fruit flies go through 4 stages
Like butterflies, fruit flies go through complete metamorphosis. In the life cycle, fruit flies pass through four stages — egg, larva, pupa and adult — and the larva stage is split into three growth steps called instars. At 25 °C (77 °F) the whole trip from egg to adult takes about nine days (Bloomington Drosophila Stock Center).
These four fruit fly life stages are the same in every kitchen and every laboratory: the drosophila melanogaster life cycle that geneticists have studied for over a century is exactly the one playing out in your fruit bowl. Whether you search for the fruit fly life cycle, "fruit flies stages" or simply the fruit flies cycle, the timeline below is the overview; each stage has its own page with the details.
| Stage | Starts (after laying) | Lasts | What happens |
|---|---|---|---|
| Egg | Day 0 | About 1 day | The embryo develops inside the egg and hatches as a tiny larva |
| Larva — 1st instar | Day 1 | About 1 day | Starts feeding, then moults |
| Larva — 2nd instar | Day 2 | About 0.9 day | Feeds and crawls through the food, then moults again |
| Larva — 3rd instar | Day 2.9 | About 2 days | Eats and grows the most, then leaves the food to pupate |
| Pupa | Day 4.9 | About 4.1 days | Inside a hard brown case, the body is rebuilt into an adult fly |
| Adult | Day 9 | Weeks | Emerges, mates and starts laying eggs 1–2 days later |
The stage timings come from FlyBase, the main Drosophila research database, which gives hatching at about 24 hours after laying, the three instars at about 25, 23 and 48 hours, and adults emerging about 220 hours after laying at 25 °C. The one thing that changes all of these is temperature — the drosophila life cycle runs on the room's warmth.
Stage 1: the egg
Every new fly starts as an egg laid on the moist surface of fermenting fruit or other damp organic matter (University of Kentucky). It hatches after about a day at 25 °C and about 2.1 days at 18 °C (64 °F), because the whole cycle slows down by the same proportion.
Stage 2: the larva
The larva is the feeding stage. It eats its way through the yeasty surface of the food, moults twice and does almost all of the fly's growing in about four days at 25 °C, then crawls out of the food to find a dry spot.
Stage 3: the hard brown case
The larva's skin hardens into a small brown case, and inside it the body is rebuilt into an adult fly over about 4.1 days at 25 °C. Then the adult breaks out, and within a day or two it is ready to mate and lay eggs.
More about the fruit fly pupa →
Fruit fly life cycle days at different temperatures
How fast do fruit flies grow? Temperature decides it. The Bloomington Drosophila Stock Center at Indiana University gives the egg-to-adult time as about 7 days at 29 °C, 9 days at 25 °C, 11 days at 22 °C and 19 days at 18 °C. A 2007 study measured almost the same: 21.8 days at 18 °C, 9.8 at 25 °C and 8.3 at 29 °C (Dillon et al. 2007). So yes — 18 °C roughly doubles the fruit fly life cycle days compared with 25 °C.
| Temperature | Egg hatches after | Larva (3 instars) | Pupa | Egg to adult | Egg to next eggs |
|---|---|---|---|---|---|
| 18 °C (64.4 °F) | 2.1 days | 8.3 days | 8.6 days | 19 days | 21–23 days |
| 20 °C (68 °F) (calculated) | 1.6 days | 6.5 days | 6.8 days | 15 days | 17–18 days |
| 22 °C (71.6 °F) | 1.2 days | 4.8 days | 5 days | 11 days | 12–13 days |
| 25 °C (77 °F) | 1 days | 3.9 days | 4.1 days | 9 days | 10–11 days |
| 27 °C (80.6 °F) (calculated) | 0.9 days | 3.5 days | 3.6 days | 8 days | 8.9–9.8 days |
| 29 °C (84.2 °F) | 0.8 days | 3.1 days | 3.2 days | 7 days | 7.8–8.6 days |
The drosophila life cycle at 25 degrees is the lab standard, which is why so many sources quote "about 10 days". Home kitchens are often cooler, so 11–15 days is more typical indoors. The extension figure of 8–10 days at 77 °F (University of Kentucky) agrees with the lab numbers. Below about 11 °C, development stops altogether (Da Lage et al. 1989, citing Cohet et al. 1980).
How are fruit flies made? Where they really come from
How are fruit flies made? Only one way: a female fruit fly lays eggs. They don't appear spontaneously from rotting fruit, but it can certainly look that way. Here is where fruit flies come from in a home:
- On the produce itself. Fruit and vegetables that were already infested in the garden, market or shop bring eggs and larvae home with them (University of Kentucky).
- Through windows and doors. Adults are strongly attracted to the smell of ripening and fermenting produce and fly in through screens that aren't fine enough; the University of Kentucky recommends tight-fitting 16-mesh screens.
- From hidden breeding spots. Drains, garbage disposals, empty bottles and cans, bins, mops and cleaning rags all hold the damp, fermenting film that the larvae live on (University of Kentucky; Iowa State University).
How do fruit flies appear out of nowhere?
Speed and size. A banana with a few invisible eggs on it can produce adults about nine days later at 25 °C, and those adults start laying their own eggs within a day or two. One rotting potato or onion can breed thousands of fruit flies (University of Kentucky). Because the eggs and larvae are so small, the first thing most people notice is a sudden cloud of adults.
How fast do fruit flies multiply?
How fast do fruit flies breed? At 25 °C, one generation — egg to adult to the next eggs — takes about 10–11 days. Fruit flies reproduction is built for speed: females store sperm after mating, start laying within a day or two of emerging and lay hundreds of eggs, so the numbers get out of hand quickly.
The calculator's second mode shows the theoretical maximum: if every egg survived, one female at 25 °C could lead to about 15,500 flies in 21 days and about 125,500 in 30 days. Real numbers are far lower, because most eggs and larvae don't survive — food runs out, larvae crowd each other and many are eaten or thrown away. But the maths explains how fast fruit flies multiply and why the source has to go, not just the adults.
Warmth speeds everything up. At 29 °C the gap between generations shrinks to about 7.8–8.6 days, while at 18 °C it stretches to about 21–23 days. For how long each adult then lives, see the fruit fly lifespan calculator.
Drosophila vs Queensland fruit fly: two different "fruit flies"
In Australia, "fruit fly" often means something else. The Queensland fruit fly (Bactrocera tryoni) belongs to a different family, the Tephritidae, and it is a serious pest of orchards and gardens rather than a kitchen nuisance. The Queensland fruit fly life cycle is slower and starts inside the fruit:
| Kitchen fruit fly (Drosophila) | Queensland fruit fly | |
|---|---|---|
| Scientific name | Drosophila melanogaster (family Drosophilidae) | Bactrocera tryoni (family Tephritidae) |
| Size | About 1/8 inch (3 mm), red eyes | About 6 mm, brown with yellow markings |
| Where eggs go | On the surface of fermenting or overripe fruit and damp organic matter | Inside ripening fruit, through punctures — up to 7 eggs a puncture |
| Egg to adult | About 9 days at 25 °C | Eggs 2–3 days, larvae 5–7 days, pupae in soil 1 week to a month or more |
| Whole life cycle | About 10–11 days from egg to egg at 25 °C | About 2–3 weeks in summer, up to 2 months in autumn |
| Starts laying | 1–2 days after emerging | About two weeks after emerging |
| Problem for | Kitchens and food businesses — a nuisance | Fruit growers — a serious crop pest |
Queensland fruit fly figures come from the California Department of Food and Agriculture's pest profile, which lists 4–5 overlapping generations a year. If you live in Australia and find maggots inside fruit on the tree, report it according to your state's biosecurity rules; the calculator on this page is for the small kitchen fruit fly.
How this fruit fly life cycle calculator works
Life cycle timeline. The total egg-to-adult time comes from the Bloomington Drosophila Stock Center's four temperatures, with straight lines drawn between them. That total is then shared out between the stages using FlyBase's 25 °C timings. Research shows that fly embryo development speeds up and slows down evenly across stages as temperature changes (Kuntz & Eisen 2014); we assume the same is true for the larva and pupa. First eggs come 1–2 days after emerging (Novoseltsev et al. 2005), scaled the same way. Dates are counted from the day you enter, or today, and rounded to the nearest day.
How fast do they multiply? Each generation's females lay about 60 eggs a day, up to 500 in total, starting about a day after emerging. Only eggs laid early enough to become adults within your time window are counted, every egg is assumed to survive, and half the offspring are female. It is a theoretical ceiling, capped at 100 starting females and 60 days.
The calculator accepts 18–29 °C (64–84 °F), the range covered by the development data.
Frequently asked questions
What is the life cycle of a fruit fly?
Egg, larva (three instars), pupa and adult. At 25 °C eggs hatch in about a day, larvae feed for about 4 days, the pupa lasts about 4.1 days and adults emerge after about 9 days.
How are fruit flies made?
Female fruit flies lay eggs on ripe or fermenting fruit and damp organic matter. The eggs hatch into larvae, which pupate and become adults — they never appear spontaneously.
How fast do fruit flies multiply?
A generation takes about 10–11 days at 25 °C and each female can lay about 500 eggs, so numbers can rise from a few flies to thousands in weeks.
How long does the fruit fly life cycle take from egg to adult?
About 9 days at 25 °C, 11 days at 22 °C and 19 days at 18 °C (Bloomington Drosophila Stock Center).
How do fruit flies reproduce?
Females mate, store the sperm and lay fertilised eggs on fermenting food, starting 1–2 days after they emerge (Novoseltsev et al. 2005) and laying hundreds over their lives (University of Kentucky).
Where do fruit flies come from?
From eggs on produce you bring home, adults flying in through screens, and hidden breeding spots such as drains, bins, bottles and mops.
What is the Drosophila life cycle at 25 degrees?
About 1 day as an egg, 4 days as a larva and 4 days as a pupa — 9 days to adult — plus 1–2 days before the new adults lay eggs.
Is the Queensland fruit fly the same as a kitchen fruit fly?
No. It is a Tephritid crop pest that lays eggs inside ripening fruit and takes about 2–3 weeks per generation in summer (CDFA).
These calculators give estimates for education. Real flies vary with strain, food, humidity and temperature. For a stubborn infestation, your local cooperative extension service can help identify the insect. We give no pesticide advice.