Woodpeckers are part of the family Picidae (240 species) that also includes the piculets, wrynecks, and sapsuckers. About 180 species of true woodpeckers constitute the subfamily Picinae, of which almost 20 species are threatened with extinction due to loss of habitat or habitat fragmentation.

They have long, sticky tongues (up to 4 inches depending on the species) with bristles that aid the woodpecker in grabbing and extracting insects from deep within a hole in a tree. It has been reported that the tongue is used to spear grubs, but more detailed studies published in 2004 have shown that the tongue instead wraps around the prey before being pulled out.

Woodpeckers can peck up to 20 times per second. Between feeding, excavating nest cavities, and drumming, this can add up to a total of 8,000-12,000 pecks per day.

The rapid pecking causes a woodpecker's skull to heat up, so they peck in short bursts with brief breaks in between, giving the head some time to cool down.

As their name suggests, acorn woodpeckers drill holes in which they stash acorns. A typical "granary tree" contains hundreds or even thousands of acorns--the largest on record contained around 50,000.

A group of woodpeckers is known as a "descent". This makes sense because most woodpeckers start at the top of trees and then work their way down.

Most species live in forests or woodland habitats, although a few species are known to live in treeless areas, such as rocky hillsides and deserts.

The majority of woodpecker species live up to their name and feed on insects and other invertebrates living under bark in trees, but the family is characterized by its dietary flexibility, with many species being both highly omnivorous and opportunistic. Their diet may include ants, termites, beetles and their larvae, caterpillars, spiders, other arthropods, bird eggs, nestlings, small rodents, lizards, fruit, nuts and sap.

A clutch will usually consist of two to five round white eggs. The eggs are incubated for 11-14 days before they hatch. It then takes about 18-30 days before the chicks are fully fledged and ready to leave the nest. In most species, soon after this the young are left to fend for themselves.

During the millisecond before contact with wood, a thickened nictitating membrane closes, protecting the eye from flying debris.