Northern populations breed in mature, moist coniferous forests. This species constructs its pendulum nests in hanging vegetation and so it is often attracted to suspended clumps of moss or coniferous twigs that are more abundant in moist spruce bogs or hemlock swamps. Southern populations breed in mature, moist, bottomland forest where Spanish moss is prevalent. Outside of the breeding season, the northern parula becomes more of a habitat generalist and may be found in a wide variety of habitats during migration and winter. These habitats may include: pastures; moist, dry or wet forests; and agricultural fields or plantations. This is a monogamous species, however, a few cases of polygamy have been reported. Southern populations can start breeding as soon as March but to the north of the range, the species does not nest until May. The breeding habitat is humid woodland with growths of Old Man's Beard lichen or Spanish moss. Northern parulas nest in trees in clumps of these fungi (Old Man's Beard; "Usnea") or plants (Spanish moss; "Tillandsia usneoides"), laying 3–7 eggs in a scantily lined cup nest. Sites located near water sources are preferred and many nests are found at the end of branches suspended over water. Due to their longer breeding season, southern parulas frequently raise two broods, as opposed to northern ones who raise only one. The female hollows out a clump of vegetation in the moss and proceeds to fill the cavity with vegetation fibers, animal hair, grass, or pine needles. These nests average in outside diameter. The incubation period typically lasts 12 to 14 days and the young fledge at 10 to 11 days. Breeding maturity is attained the following year. The northern parula forages mostly or entirely on terrestrial invertebrates. Prey items include spiders, damselflies, locusts, bugs, grasshoppers, aphids, beetles, caterpillars, flies, wasps, bees, and ants. Regardless of season, caterpillars and spiders are consumed most often. During the winter, the northern parula consumes more beetles and occasionally forages on berries, seeds, and nectar. This species primarily captures prey from vegetation by a hover-glean method, however this species is versatile in using a variety of foraging methods. It may make short flights from a perch to snatch prey in mid-flight or even hang upside-down to forage. It is most often seen foraging in the mid- to upper canopy levels of vegetation.