Worms or Maggots Inside Blueberry Fruit — What Are They?

Biting into a blueberry and finding a small white worm or maggot inside is alarming. The berries may look perfectly normal from the outside — no holes, no skin damage — and yet inside the flesh there are tiny larvae tunnelling through. Two pests are responsible for the vast majority of cases: spotted wing drosophila and the blueberry maggot fly. Both are fly larvae, both are small and white, and both can devastate a crop if not managed. Telling them apart matters because their management differs.

Spotted wing drosophila (SWD)

Spotted wing drosophila (Drosophila suzukii) is an invasive fly that has become the dominant blueberry pest across Europe and North America over the past fifteen years. Unlike other fruit flies that only attack overripe or damaged fruit, SWD females cut into firm, ripening berries using a serrated ovipositor and lay eggs inside. The larvae hatch and feed within the berry, causing it to soften and collapse. Affected berries often look fine until they suddenly become mushy. SWD populations peak in late summer, so late-ripening varieties are more exposed. Physical exclusion using fine mesh fruit cage netting with an aperture of one millimetre or less is the most reliable control. Harvest frequently and promptly — SWD prefers fruit left on the bush beyond peak ripeness.

Blueberry maggot fly

Blueberry maggot fly (Rhagoletis mendax) is a North American pest. The adult fly resembles a small housefly with distinctive wing banding and lays eggs under the skin of ripening berries. The larvae tunnel through the flesh, making the berry soft and dropping it prematurely. Unlike SWD, blueberry maggot larvae are somewhat larger and the entry wound from the egg-laying is sometimes visible as a small dimple or discolouration. Monitoring with yellow sticky traps and perimeter sprays of approved spinosad-based products applied to foliage before berries ripen provides control.

How to tell them apart

SWD larvae are very small — about three millimetres — and the infested berries tend to collapse rather than drop. Blueberry maggot larvae are slightly larger and the berries more often fall intact. Both pests require early action and monitoring rather than reactive treatment once the infestation is inside the fruit. Submerging harvested berries in salt water will cause any larvae present to exit the berry, which is useful for confirming infestation.

Cultural practices that help

Pick berries frequently — every two to three days at the height of the season — rather than waiting for large harvests. Collect and destroy all fallen or overripe berries immediately, as these are both an attractant and a breeding site. Remove and freeze or hot-compost infested fruit; do not leave it near the garden. A properly fitted fine-mesh fruit cage remains the single most effective physical barrier for both pests.