Look: a barrel-shaped case about 3 mm long; white at first, then tan and brown and brittle, with red eyes and black wings showing through near the end (Tyler; Bainbridge & Bownes 1981). How long: about 4.1 days at 25 °C (77 °F), 5 at 22 °C and 8.6 at 18 °C (FlyBase; Bloomington). Where: dry surfaces near the food — fruit bowl rims, container walls, bin lids and bags, kitchen walls.
Fruit fly pupa: what it looks like
A fruit fly pupa is a small, barrel-shaped case, roughly 3 mm long (Magee & Spokony 2023), stuck to a dry surface near the food the larva grew up in. The case — called a puparium — isn't a new skin. It is the hardened skin of the fully grown third-instar larva, which shortens, toughens and darkens around the developing fly (Vanderbilt; Tyler). At the front end you can often see two tiny horn-like stalks: the larva's breathing spiracles, pushed out just before it pupated.
So, what do fruit fly pupae look like from day to day? They change colour. The puparium "is initially soft and white but soon hardens, turning tan and eventually brown and brittle" (Tyler). In the lab, the white stage lasts only about an hour at 25 °C and the case is brown within about three hours (Bainbridge & Bownes 1981, via Tyler). After that the outside stays brown, but the developing fly starts to show through it.
Fruit fly pupa colour and what it tells you
The fruit fly pupa colour is the best clue to how close the adult is. Developmental biologists stage pupae by what they can see through the case, and the timings at 25 °C are well documented:
| Stage | Hours | What you can see |
|---|---|---|
| P1 | 0–1 | White puparium; the larva stops wriggling |
| P2 | 1–3 | Brown puparium |
| P5 | 12.5–25 | Legs and wings extend inside the case |
| P8–P9 | 47–69 | Eyes turn yellow, then deep amber |
| P10 | 69–73 | Eyes bright red |
| P12 | 73–78 | Wings turn grey |
| P13 | 78–87 | Wings turn black |
| P15 | 90–103 | Legs twitch; the adult fly emerges |
Times are from Bainbridge and Bownes's 1981 staging series, as reproduced in Tyler's lab chapter; individual pupae vary. The practical version is the four looks in the calculator: pale (just formed), tan to brown with nothing visible (the first two to three days), red eyes showing and black wings showing — at which point the fly is less than a day from emerging at room temperature.
| Pupa look | Age of the pupa | Time left (calculator) |
|---|---|---|
| Pale or white | 0–1 h | 4.1–4.1 days |
| Tan to light brown | 1–69 h | 30 hours–97 hours |
| Brown, red eyes showing | 69–78 h | 22 hours–30 hours |
| Dark, black wings showing | 78–90 h | 9.8 hours–22 hours |
Brown pupae on the fruit bowl
Little brown pupae on fruit bowl rims, a fruit crate, the bin lid or a bin bag are a sure sign that fruit flies have completed their whole development there. The University of Kentucky's small-flies fact sheet illustrates exactly this: fruit fly pupae clustered on a trash bag. Empty cases with a split, open front end mean the adults have already left.
How long is the fruit fly pupa stage?
About four days in a warm room. FlyBase puts the pupal period (including the brief prepupa) between about 120 and 220 hours after the egg was laid at 25 °C — about 4.1 days — and Tyler's lab chapter gives 3–4 days. Like every stage, it slows down as the room cools:
| Temperature | Pupa stage lasts | Case forms (after laying) | Adults emerge (after laying) |
|---|---|---|---|
| 18 °C (64.4 °F) | 8.6 days | Day 10.4 | Day 19 |
| 20 °C (68 °F) (calculated) | 6.8 days | Day 8.2 | Day 15 |
| 22 °C (71.6 °F) | 5 days | Day 6 | Day 11 |
| 24 °C (75.2 °F) (calculated) | 4.4 days | Day 5.3 | Day 9.7 |
| 25 °C (77 °F) | 4.1 days | Day 4.9 | Day 9 |
| 27 °C (80.6 °F) (calculated) | 3.6 days | Day 4.4 | Day 8 |
| 29 °C (84.2 °F) | 3.2 days | Day 3.8 | Day 7 |
These durations use the Bloomington Drosophila Stock Center's egg-to-adult times at 18, 22, 25 and 29 °C, shared out with FlyBase's 25 °C stage timings, so they match our egg, larvae and life cycle tools exactly. So how long do fruit flies stay in pupa? About 4.1 days at 25 °C (77 °F), 5 at 22 °C (72 °F) and 8.6 at 18 °C (64 °F).
When do fruit flies emerge from pupae?
At the end of that period the adult splits the front of the case along its seams and pushes out (Tyler). Emergence is timed by the fly's internal clock: in the lab it happens mostly around dawn, and a pupa that misses dawn by a few hours usually waits until the next morning (Tyler). So if you see dark-winged pupae in the evening, expect new flies the next morning. New females don't have ripe eggs until about two days after they emerge (Tyler), which is the last window to catch them before the next round of eggs.
Where fruit flies pupate in your home
Where do fruit flies pupate? Not in the food. A fully grown larva crawls up and out of its food to find a relatively clean, dry place before it stops and forms its case (Vanderbilt; Tyler). That's why pupae turn up a short distance from the source:
- Fruit fly pupae on wall surfaces beside or behind a fruit bowl, compost caddy or bin, and on the underside of shelves above them.
- On containers: the sides and rims of fruit bowls, crates, jars and the inside of bin lids. In a culture bottle, larvae pupate all over the dry walls (Tyler); keepers of feeder flies see the same thing in culture cups (Reptile Deli).
- On bags and packaging, such as a bin bag or a produce bag left on the counter (University of Kentucky).
- Fruit fly pupae in drain pipes and plugholes: larvae breeding in drain slime also have to leave the wet film to pupate, so look on the drier parts of the drain, the overflow or the plug, rather than in the water itself.
Against a light-coloured wall or bowl the brown cases are easy to spot once you know what to look for; on dark surfaces, a torch held low to the side helps.
Fruit fly metamorphosis: from pupa to adult
Fruit flies go through complete metamorphosis, and the pupa is where it happens. How do fruit fly larvae turn into flies? Not by growing wings on the larva. Inside the case, most of the larva's body is broken down, and the adult is built from groups of cells it has carried, unused, since it was an embryo (Tyler):
- Imaginal discs — small, folded packets of cells for the wings, legs, eyes, mouthparts and genitals — grow throughout larval life without changing shape. In the pupa they turn inside out and develop into adult parts (Tyler; Vanderbilt).
- Histoblasts, small nests of cells, build the adult abdomen and internal organs (Tyler).
- Some larval organs are kept and remodelled, including the nervous system, the excretory Malpighian tubules and the fat body (Tyler). Breaking down larval tissue supplies the raw material and energy for all this (Vanderbilt).
The sequence through the case is the one in the colour table above: the head, legs and wings turn out within the first day; the eyes colour from yellow to amber to red over days two and three; then bristles and wings darken, and a green patch of waste (the meconium) appears at the tip of the abdomen just before the adult emerges (Bainbridge & Bownes 1981, via Tyler). For where the pupa fits among the other stages, see the fruit fly life cycle calculator.
Fruit fly pupae vs other fruit fly pupae
"Fruit fly" covers several very different insects, and where they pupate is one of the easiest ways to tell them apart:
- Household fruit flies (Drosophila melanogaster) pupate on dry surfaces next to the food, indoors, and emerge in about four days.
- Spotted wing drosophila, the berry pest, has cylinder-shaped, reddish-brown pupae 2–3 mm long, formed either inside or outside the fruit (Oregon State University).
- Tephritid fruit flies — a different family — mostly pupate in soil. Blueberry maggot larvae burrow about an inch down (UF/IFAS); the Queensland fruit fly spends a week (warm weather) to a month or more (cool weather) as a pupa in the soil (CDFA); olive fruit fly larvae pupate inside the fruit in summer but drop to the soil in autumn (UC IPM).
Hydei pupae in feeder-fly cultures
If you keep feeder flies, you'll see two kinds of pupae in culture cups. A Drosophila hydei pupa belongs to the larger species — adults about 4–5 mm against 2–3 mm for melanogaster (Reptile Deli) — and its cultures take noticeably longer to produce: about 16–25 days to the first new flies, against 9–14 for melanogaster. Our flightless fruit fly culture calculator covers both.
How to get rid of fruit fly pupae
Pupae don't eat, so traps and baits don't touch them. The only way to stop them becoming flies is to remove them — and the source they came from. These non-toxic steps follow extension advice to find and eliminate breeding sites (University of Kentucky; Iowa State University):
- Wipe or scrape the cases off walls, containers and bin lids with a damp cloth or paper towel, and put them in the bin outside.
- Clean the surface with hot, soapy water once the cases are off.
- Find the food the larvae came from — usually within arm's reach — and bin it, sealed.
- Do it before the date in the calculator: once the wings are dark, adults emerge within about a day at room temperature.
- Replace bin bags with pupae on them, and rinse the bin.
Cold pauses pupae rather than reliably killing them — development stops below about 11 °C — so wipe them off rather than relying on the fridge (see what cold and the fridge do to fruit flies).
How this fruit fly pupa timer works
The timer uses the same development model as our egg, larvae and life cycle calculators. The pupal stage takes 100 of FlyBase's 220 hours from egg to adult, and the Bloomington Drosophila Stock Center's egg-to-adult times (7, 9, 11 and 19 days at 29, 25, 22 and 18 °C) set how long that is at your temperature. Each pupa look is matched to its age in Bainbridge and Bownes's 25 °C staging: pale 0–1 hours, tan or brown 1–69 hours, red eyes 69–78 hours and black wings 78–90 hours after the case forms. The time left is the rest of the 100-hour pupal stage, scaled to your temperature, so you get a range from the youngest to the oldest pupa with that look. Dates count from the day you found them and are rounded to the nearest day; found-dates can't be in the future or more than 30 days back.
The "tan to brown" look covers almost three days, so its range is wide. Check again in a day or two: once red eyes or dark wings show, the estimate narrows to hours.
Frequently asked questions
What does a fruit fly pupa look like?
A small brown, barrel-shaped case about 3 mm long, stuck to a dry surface near the food. It starts white, turns tan and then brown, and red eyes and black wings show through it near the end.
How long is the fruit fly pupa stage?
About 4.1 days at 25 °C (77 °F), 5 at 22 °C and 8.6 at 18 °C, based on FlyBase and Bloomington development data.
When do fruit flies emerge from pupae?
When the pupal stage ends — about four days after the case forms at 25 °C. Emergence is mostly around dawn (Tyler).
Where do fruit flies pupate?
On a relatively clean, dry surface near their food: fruit bowl rims, container walls, bin lids and bags, kitchen walls and the dry parts of drains.
Why are there brown pupae on my fruit bowl?
Fruit fly larvae grew in fruit or juice in the bowl, crawled out and pupated on its rim. Bin the fruit and wipe the cases off.
What does it mean if I can see red eyes in the pupa?
The fly is late in development: red eyes appear about 69–73 hours after the case forms at 25 °C, so adults will emerge within about a day or so.
How do you get rid of fruit fly pupae?
Wipe or scrape them off, put them in the outside bin, clean the surface and remove the food the larvae came from. Traps don't affect pupae.
Are empty fruit fly pupal cases a problem?
They show flies have already emerged there. The cases themselves are harmless, but find and remove the breeding source nearby.
Do Tephritid fruit flies pupate the same way?
No. Most, such as the blueberry maggot and Queensland fruit fly, pupate in the soil under the plant rather than on surfaces indoors.
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.