Worm-eating Warbler, Helmitheros vermivorum

The Worm-eating Warbler's name comes not for this warbler's habit of eating earthworms, but for eating large quantities of caterpillars. This is an inconspicuously marked warbler, found in the dense understory of steep slopes in the eastern deciduous forests. Its song, while distinctive, might be mistaken for an insect's buzz. 

The Worm-eating Warbler is found mainly from southern Connecticut to northern Alabama and Georgia during the breeding season, it forages low to the ground, often probing hanging clusters of dead leaves.  During the non-breeding season, it largely specializes on these dead leaf clusters when in southern Mexico, northern Central America, and the Caribbean.  In Tennessee, the Worm-eating Warbler is present from mid-April through early September primarily in East and Middle Tennessee.

Description: This stocky, flat-headed, overall buffy-olive warbler has distinct black crown stripes and a black stripe through the eye. The male and female look the same.

Length: 5.25"
Wingspan: 8.5"
Weight: 0.46 oz

Voice: The song is an insect-like flat, dry, rapid trill.

Similar Species:

Habitat: Breeds in large tracts of mature deciduous or mixed deciduous-coniferous forest with patches of dense understory, usually on steep slopes.

Diet: Insects, spiders, slugs, and especially caterpillars.

Nesting and reproduction: The female occasionally returns to the same territory in successive years. Egg laying in Tennessee begins as early as the end of April and likely peaks in early May.

Clutch Size: Typically 4 or 5 eggs are laid.

Incubation: The female alone incubates the eggs for about 13 days.

Fledging: The young are fed by both parents, and leave the nest about 10 days after hatching.

Nest: The female builds the well-concealed cup-nest on the ground from skeletonized dead leaves, and lines it with moss.

Status in Tennessee: The Worm-eating Warbler is an uncommon to fairly common migrant across the state and a fairly common summer resident in East and the Western Highland Rim of Middle Tennessee.  It arrives in mid-April and departs by early September.

Populations appear to be declining in the state. The Worm-eating Warbler appears on the Audubon Watchlist due to threats of forest fragmentation on the breeding grounds, and deforestation on the wintering grounds.

Fun Facts:

  • The female relies so much on her cryptic coloration that she will not flush while incubating unless actually touched. When she does flush, she performs a distraction display fluttering and twittering along the forest floor, with wings and tail spread in an effort to lure the would-be predator away from the nest.
  • The oldest known Worm-eating Warbler in the wild was 10 years, one month old.

Obsolete English Names:

Best places to see in Tennessee: Edgar Evins SPFrozen Head State Natural AreaNorth Cumberland WMAGreat Smoky Mountains NP.