A bog is a wetland type that accumulates peat, a deposit of dead plant material. The term peat bog in common usage is therefore somewhat redundant, although it would be proper to call these sphagnum bogs if the peat is comprised mostly of acidophilic moss (peat moss or Sphagnum spp.). Lichens are a principal component of peat in the far north. It is typical of bogs that they have no significant inflows or outflows. Moisture is provided by condensation. Bog waters are acidic due to the accumulated decaying vegetation.

Bogs are distributed in cold, temperate climates, mostly in the northern hemisphere (Boreal). Sphagnum bogs are widespread in northern Europe. Ireland is more than 15 per cent bog; Achill Island off Ireland is 87 per cent bog. There are extensive bogs in Canada (called muskegs), Scotland, Finland, and Russia. There are also bogs in the Falkland Islands.

There exist other terms for what are bogs or peat wetlands similar to bogs. The term moor refers to a flat, boggy area with patches of heath and peat moss (i.e., a bog). An example of this wetland type is the vast expanse of moorland in south-west England, Dartmoor.

Bog habitats

Bogs are habitats for carnivorous plants, because bogs provide few nutrients. They also offer a unique environment for animals. For instance, English bogs give a home to the boghopper beetle and a yellow fly called the hairy canary.

Some bogs have preserved ancient oak logs useful in dendrochronology and they have yielded extremely well-preserved bog bodies, with organs, skin and hair intact, such as Tollund Man and Lindow man, buried there thousands of years ago after apparent Celtic human sacrifice.

Uses of bogs

A bog is a very early stage in the formation of coal deposits. In fact, bogs can catch fire and often sustain long-lasting smoldering blazes, producing smoke and CO2 causing health and environmental problems. After drying peat is used as a fuel. More than 20 per cent of home heat in Ireland comes from peat and it is also used for fuel in Finland, Scotland, Germany, and Russia. Russia is the leading producer of peat for fuel at more than 90 million metric tons per year.

The other major use of dried peat is as a soil amendment (sold as peat moss or sphagnum) to increase the capacity to retain moisture and enrich the soil. It is also used as a mulch

These industrial uses of peat threaten the continued existence of bogs. More than 90 per cent of the bogs in England have been destroyed.

Sphagnum bogs are also used for sport. Bog snorkeling is popular in England and Wales and has even produced the associated sport of mountain bike bog snorkeling. Llanwrtyd Wells, the smallest town in Wales, hosts the World Bog Snorkelling Championships. In this event, competitors with mask, snorkel, and scuba fins swim along a 60-meter trench cut through a peat bog.

July 30 is International Bog Day.