Dept. of Horticulture

Education and research for a green world

Life of the Cabbage Maggot

Cabbage maggots, Delia radicum L., are members of the fly family, Anthomyiidae, in the order Diptera. They are exotic pests originally from Europe and have been recorded in the US since the 1800's. Delia can cycle through 3–5 generations a year in the northern Willamette Valley, depending on the weather and soil conditions (Fig. 1).

Jump to: Eggs | Larvae (Maggots) | Pupae | Flies

Life Cycle

Cabbage maggots overwinter as small, brown pupae in the soil and will not emerge until temperature warms up in the spring. The onset of spring emergence occurs around early March, depending primarily on temperature and precipitation. The average spring flight peak-emergence (50% population) over 4 years of data was documented on April 4th (accumulation of 600°F DD; see degree-day modeling). Male flies emerge 4–6 days before the females. Flies have an extended period of mating (2–5 weeks). Females are required to feed on nectar from flowering plants for a nutritional protein and carbohydrate source before egg-laying. Egg-laying begins approx. 7–14 days after adult emergence. Small (1 mm) eggs are laid in and around the soil surface near the base of the host plant. Females can lay an average of 100–200 eggs. Eggs hatch within 3–7 days and develop into larvae that feed and tunnel into roots of host plants for 2 to 3 weeks. When maggots are fully grown, they usually leave the root and form a brown protective case (pupae) in the soil at depths of 5-15 cm (2-6 inches). A complete cycle from egg to adult fly takes approximately 40–65 days.

Photo of Life Cycle

Fig. 1. The life cycle of the cabbage maggot.

Indentification Return to top of page
Eggs Photo of Eggs

Eggs characteristics:

White and oblong-shaped
1–mm long
May find eggs in clumps
Longitudinal striations on surface of egg

Eggs are deposited in soil cracks within a 2 cm radius around plant base.

Larvae (Maggots) Return to top of page Photo of Larvae

Maggot characteristics:

White color
No legs
Blunt at one end, pointed on the other end
Circular arrangement of double spines around blunt end

Three developmental stages:

Small (1–3 mm)
Medium (3.1–5 mm)
Large (5.1–8.5 mm)

Burrow into roots of Brassica plants and feed on the root tissues.
Feed for 2–4 weeks before developing into pupae.

Pupae Return to top of page Photo of Pupae

Pupae characteristics:

Brownish-red color, 5-6 mm
Found in the soil around root

Cabbage maggots remain in the pupae stage for about two weeks. However, if they do not pupate until late fall, they will “overwinter” and not emerge from the soil as flies until spring.

Flies Return to top of page Photo of Adult Fly

Fly characteristics:

½ the size of a housefly
Ash to dark gray color
Darker stripes on thorax (back)
Covered in black bristles
Prealar bristle is shorter than other bristles on thorax
Females slightly larger than male flies
Antennae almost bare, not plumose
See (1) wing venation and bristle (2a and 2b) arrangement on thorax, and on (3a and 3b) legs below:

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