Apple maggot
A fruit fly about the size of a housefly or a little smaller, native to eastern North America, where it originally lived on hawthorn. Females lay eggs under the skin of apples from early summer, and the small white maggots tunnel through the flesh, leaving brown winding trails. That is why it is also called the railroad worm. Infested apples can be dimpled, lumpy and rotten inside. Red sticky sphere traps show when the flies are active, and bagging the fruit, kaolin clay and prompt removal of dropped apples protect a home tree.
Adult Rhagoletis pomonella on apple skin, showing the dark banded wings and white thorax spot. Photo: pending.
Identification
The adult is 3/16–1/4 inch long, about the size of a housefly or slightly smaller (sources differ), with a black body. The tells are a conspicuous white spot where the thorax meets the abdomen, white bands across the abdomen (three on males, four on females), and clear wings crossed by black bands that form a rough letter F. The eyes are dull red.
The larva is a small, whitish, cylindrical maggot, about 1/4 inch long when grown, with dark mouth hooks. It is rarely seen and much smaller than a codling moth larva. The pupa in the soil looks like a large, dark brown grain of wheat.
Easily confused with
- Codling moth larvaAlso a pestA codling moth caterpillar is much larger, bores to the core and leaves a hole plugged with brown frass; apple maggot leaves only pinpricks outside and brown threadlike trails through the flesh.
- Plum curculioAlso a pestPlum curculio cuts small crescent-shaped scars on newly set fruit in spring; apple maggot damage begins later, in summer, as tiny egg punctures and dimples.
- Other small flies on the treeHarmlessApple maggot flies stand out from other flies by their black bodies and the black F-shaped bands on otherwise clear wings, plus a white spot on the thorax.
Damage symptoms
The female lays single eggs just under the skin, and each puncture can leave a pit or dimple. In some varieties there is no outward sign at all. The maggots break down the flesh as they tunnel, and decay organisms follow them, leaving brown, winding trails that widen as the larvae grow. Heavily infested apples become lumpy, distorted and inedible, and some drop early. Early-maturing varieties are the most vulnerable.
- Tiny pinprick egg punctures on the skin, often with a small dimple
- Lumpy, dimpled or distorted fruit when many eggs are laid
- Brown, threadlike trails winding through the flesh when the apple is cut
- Soft, rotting flesh inside fruit that looks sound outside
- Early fruit drop in heavy infestations
Lifecycle & degree days
The insect spends the winter as a pupa in the soil under host trees. Adults emerge from late June to early July in Minnesota, stay active into September or later, and peak from late July to early August. Cornell's NEWA model, as cited by University of Minnesota, puts emergence at about 796–1,072 degree days (base 50 °F). Females begin laying 7–14 days after emerging (sources differ) and can lay up to about 200 eggs. The larvae feed for about 2–4 weeks (sources differ), usually finishing in fallen fruit, then drop to the soil to pupate. There is usually one generation a year; NC State reports two below about 1,200 feet in western North Carolina, where emergence can run from late May to August.
- Adult emergence
- ~796–1,072 degree days °F (base 50 °F); late June–early July in Minnesota
- Peak flight
- Late July to early August
- Pre-egg-laying period
- 7–14 days after emergence
- Generations / yr
- 1; 2 at low elevation in western North Carolina
- Overwinters
- Pupae, in the soil under host trees
Host crops
Apple, crabapple, quince and the native host, hawthorn. The PNW handbook calls pear, plum and tart cherry incidental hosts; Utah State also lists apricot and cherry, and reports it only sporadically in Utah backyard plums and apples. Because those are minor hosts, this page is not listed under stone fruit. NC State warns that abandoned orchards, a few unsprayed trees or wild hawthorns within about 400 yards can supply the flies that reach a sprayed tree.
Monitoring & action thresholds
This is University of Minnesota's home-orchard figure: act as soon as a red sphere without a lure catches one fly, or when a lure-baited sphere has caught five in total. Its fruit-production blog puts the first spray 7–10 days after the threshold is reached. NC State uses a cumulative catch of 5 flies on baited spheres, and repeats the spray every 14 days whenever the catch reaches 5 again.
Hang bright red spheres at least 3 inches across, coated with sticky tanglefoot, from late June or early July. University of Minnesota suggests one trap per 100 fruit after thinning: one or two on a small tree, five or more on a large one. A fruity-scented lure makes them catch more. Check the traps weekly, and clean off the insects and recoat them as needed. Yellow sticky cards also catch the flies, but they catch many other insects too. Mainly, the traps tell you when to act. The PNW handbook says enough traps (one on a small tree, two to four on a medium tree, six to eight on a 20–25 ft tree) can manage a low fly population on a home tree, but not a high one; University of Minnesota notes that mass trapping an orchard would need about 400 traps per acre.
Biological control
No beneficial sold or profiled on this site has shown control of apple maggot in apples. The PNW handbook notes that little effective biological control has been seen, because the maggots feed inside the fruit, out of reach. In pot tests, Steinernema riobrave and Steinernema carpocapsae were the nematodes most virulent to apple maggot pupae in soil. The researchers suggest spring applications under the canopy before the adults emerge, but no field trial was found. Parasitic wasps attack the maggots in wild hawthorn fruit (overall parasitism was 27% in a survey of hawthorns in two midwestern US states), but that is in hawthorn, not in apple trees.
Cultural controls
On a backyard tree, the non-spray options keep the flies off the fruit or stop the larvae reaching the soil. University of Minnesota reports that kaolin clay and exclusion netting protect most of the fruit without insecticide, and the PNW handbook calls sanitation one of the most effective strategies in home orchards.
- Bag each apple in a plastic sandwich bag after thinning, and snip the bottom corners so water can drain out
- Keep a visible coating of kaolin clay on the leaves and fruit; University of Minnesota reports that a well-kept coating protects about 90% of the fruit
- Net the whole tree: University of Minnesota research found hail netting excluded an average of 96% of the flies in a commercial orchard
- Pick up every dropped apple during the season and after harvest, and bin it in a sealed bag rather than composting it at home
- Spread tarps under the tree to stop larvae in fallen fruit from reaching the soil
- Abandoned apple trees and wild hawthorns nearby supply flies (NC State); remove them where you can, or hang traps in them as University of Minnesota suggests
Chemical, last resort
- SpinosadREI 4 h
- EsfenvalerateREI 12 h
Sources
University of Minnesota Extension, Apple maggots (Schuh, Wimmer, Hahn et al., reviewed 2026)
University of Minnesota Extension, Preparing for apple maggot management in 2026 (Wimmer, 2026)
NC State Extension, Apple Maggot (Walgenbach, 2015)
Pacific Northwest Insect Management Handbook, Apple — Apple maggot
Utah State University Extension, Apple Maggot (fruit IPM advisory)
Usman et al., Entomopathogenic nematodes against apple maggot pupae, J. Nematology 2020
Rull et al., Parasitoids of hawthorn-infesting Rhagoletis, Environ. Entomol. 2009
UC IPM, Relative Toxicities of Insecticides Used in Apples to Natural Enemies (2015)
UC IPM Pest Management Guidelines: Apple — Codling Moth (treatment table)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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