Adult worm-eating warbler upperparts are brownish olive, with a buff-orange head with a black eyeline and a black line on either side of the buffy crown. The bill is pale and long. Underparts grade from buff orange on throat and breast to less bright on belly and undertail feathers. Call is a seedy trill, a rapid series of nonmusical chips resembling the song of a chipping sparrow but which is much more rapid. The song may be mistaken for an insect. Call is a hard seep or tchip.
Similar species: The distinct black eyestripe and pair of crown stripes separates the worm-eating warbler from Swainson’s warbler (which is also much browner and has a brown cap) and red-eyed vireo (which is darker, has a gray crown, and, like other vireos, has a thicker bill, with a small hook at the tip).
Length: 5¼ inches.
Statewide, except for northwestern Missouri and the Bootheel lowlands. Most likely to be seen in southeastern half (Ozark uplands), increasingly less common in northwest, where large unbroken forests and woodlands become rarer.
Habitat and Conservation
Found on steep, wooded slopes and ravines, usually in drier areas and places with a dense understory, foraging near the ground. Its need for wooded habitat makes it rare in northern Missouri, where such habitat is limited. It is one of four Missouri warblers most closely associated with large tracts of upland deciduous forest in the Ozarks, and called forest interior birds. The other three warblers in this category are the black-and-white warbler, ovenbird, and Kentucky warbler.
Forages among shrubs near the ground for insects, mostly caterpillars of moths and butterflies, which many people would simply call “worms.” This explains the common name and both parts of the scientific name (Greek hélmins, worm, + thēros, hunter; and Latin vermi, worm, + vorum, eating). This species also eats several other types of arthropods, including spiders, as well as slugs. True earthworms, however, are not on the menu — no matter which language you use.
As summer resident, uncommon in southern Missouri and rare in northern Missouri.
Nests are built on the ground and are made from skeletonized leaves and lined with moss. Clutches comprise 3–6 eggs; the young can leave the nest 8–10 days after hatching, sometimes earlier. Incubating females often cling tight to the nest and will not leave it unless forced. Their drab coloration tends to protect them from being discovered, so it usually pays off to sit tight. If they are flushed from the nest, they flit around on the ground nearby, trying to distract the potential predator from the nest. They are present in Missouri May–September; they winter in Cuba, Puerto Rico, parts of Mexico, and south to Costa Rica.
Many forest interior birds — birds that need large, unbroken tracts of forests in order to survive — decline as a direct result of human construction projects. When we put in roads, homes, housing developments, businesses, and so forth, creating open areas in the woods, cutting up large forests, many species decline, directly or indirectly, as a result. Some may even go extinct.
Because many species require large, unbroken tracts of forests, conservationists try to preserve these large tracts, and also to find ways to keep the various tracts connected to each other with a network of similar, adjoining habitats. This is true of all kinds of habitats (such as prairies), and not just of forests.