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Adult. Photo: William Sherman/iStock

Worm-eating Warbler

Helmitheros vermivorum

A dry trilled song in the undergrowth of deciduous woods in summer announces that the Worm-eating Warbler is at home. Less colorful than most of its relatives, it is also more sluggish, foraging deliberately in the woodland understory or on the ground, probing among dead leaves with its rather long bill. Despite the name, it does not feed on earthworms; it does eat caterpillars, but no more than many other warblers.

Conservation status	Has disappeared from some areas with clearing of forest. Current numbers probably stable. Will become more vulnerable to parasitism by cowbirds where forest is broken up into smaller patches.
Family	Wood Warblers
Habitat	Leafy wooded slopes. During breeding season, frequents dense deciduous woodlands. Prefers cool, shaded banks, sheer gullies and steep, forested slopes covered with medium-sized trees and an undergrowth of saplings and shrubs. In winter in the tropics, forages alone in dense thickets or in the forest undergrowth, usually near the ground.

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Feeding Behavior

Forages mostly in trees and shrubs. Probes in curled, dead leaves for insects, and searches on bark of trunks and limbs. Forages also on the ground, walking while seeking insects on the leaf-litter.

Eggs

4-5, sometimes 3-6. White, with brown spots and blotches. Incubated by female alone, 13 days. In most areas, rarely parasitized by cowbirds, possibly because it breeds mainly in dense woods far from edges. In some areas, parasitism by cowbirds appears to be more common. Young: Fed by both parents. Leave the nest at 10 days of age. Probably 1 brood per year.

Young

Fed by both parents. Leave the nest at 10 days of age. Probably 1 brood per year.

Diet

Mostly insects. Eats smooth caterpillars, but rarely or never takes the earthworms that the name would seem to imply. Also feeds on small grasshoppers, bugs, ants, bees, walkingsticks, beetles, sawfly larvae, and spiders. Feeds nestlings on moths and grubs.

Nesting

Males defend territories by singing from perches at mid-levels or on the ground. Besides the usual insect-like trill, male also sings a musical, varied song during flight as part of courtship. Nest: Placed on ground, normally on hillside against a deciduous shrub or sapling, well concealed by dead leaves. Nest (constructed by female) is an open cup of dead leaf skeletons; lined with fungus filaments, hair moss, maple seed stems, animal hair.

Illustration © David Allen Sibley.
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Text © Kenn Kaufman, adapted from
Lives of North American Birds

Migration

Migrates mostly at night. Fall migration begins early, many moving south in August. Very rare stray in west, mostly in fall.

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Migration

Migrates mostly at night. Fall migration begins early, many moving south in August. Very rare stray in west, mostly in fall.

All Seasons - Common
All Seasons - Uncommon
Breeding - Common
Breeding - Uncommon
Winter - Common
Winter - Uncommon
Migration - Common
Migration - Uncommon

Songs and Calls

Song like that of Chipping Sparrow, but faster, buzzy, and more insect-like.

Audio © Lang Elliott, Bob McGuire, Kevin Colver, Martyn Stewart and others.
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How Climate Change Will Reshape the Range of the Worm-eating Warbler

Audubon’s scientists have used 140 million bird observations and sophisticated climate models to project how climate change will affect this bird’s range in the future.

Zoom in to see how this species’s current range will shift, expand, and contract under increased global temperatures.

Climate Threats Near You

Climate threats facing the Worm-eating Warbler

Choose a temperature scenario below to see which threats will affect this species as warming increases. The same climate change-driven threats that put birds at risk will affect other wildlife and people, too.