monitor, any of various dragonlike, mostly tropical lizards. A monitor lizard has a heavy body, long head and neck, long tail that comes to a whiplike end, and strong legs with sharp claws. Its slender, forked tongue is protrusible. Monitors range in size from the 8-in. (20-cm) short-tailed species of W Australia to the 10-ft, 300-lb (3-m, 136-kg) Komodo dragon, the giant among living lizards, that lives only on the small Indonesian island of Komodo. Some monitor species spend their lives in trees, and others inhabit lakes and rivers; they can be found on the oceanic islands and continents of the Eastern Hemisphere in all types of warm habitats, from tropical forest to desert. They feed on various kinds of animal matter, including eggs, rats, frogs, and decaying meat. The larger species will attack small deer and pigs. They often tear the prey with claws and teeth, but generally swallow it whole or in large chunks. Monitors lay from 7 to 35 leathery eggs, usually in holes in the ground or in trees. They are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, family Varanidae, genus Varanus.

monitor, type of turreted warship (no longer used) carrying heavy guns, having little draft, and lying low in the water. Monitors were so called from the first of the class, the Monitor, built for the Union navy in the U.S. Civil War by John Ericsson. Launched in Jan., 1862, the Monitor was 179 ft (55 m) long, of 41.5-ft (13-m) beam, and weighed 1,200 tons. A revolving turret, protected by 8 in. (20.3 cm) of iron armor and containing two 11-in. (27.9-cm) smooth-bore guns, was its main feature. The sides were covered by iron plates from 3 to 5 in. (7.6-12.7 cm) thick, with about 27 in. (69 cm) of wood backing, and the deck, only 18 in. (46 cm) above water, was shielded with 1-in. (2.54-cm) armor. The ship was moved by steam power, with a screw propeller. (See Monitor and Merrimack for more information.) Monitors were used extensively in the Civil War, but the type had limitations—it was too heavy to navigate the oceans—and was eventually abandoned. However, they were used by the British navy in World War I.

Monitor and Merrimack, two American warships that fought the first engagement between ironclad ships. When, at the beginning of the Civil War, the Union forces abandoned the Norfolk Navy Yard at Portsmouth, Va., they scuttled the powerful steam frigate Merrimack. She was subsequently raised by the Confederates, converted into an ironclad, and renamed the Virginia. On Mar. 8, 1862, the Virginia, commanded by Capt. Franklin Buchanan, sallied forth into Hampton Roads against the wooden ships of the Union blockading squadron. She rammed and sank the Cumberland, destroyed the Congress after running her aground, and scattered the remaining ships, all the while sustaining practically no damage to herself.

The next day, however, the Virginia, now under command of Lt. Catesby Jones, was challenged by the strange-looking Union ironclad Monitor (see monitor), built by John Ericsson and commanded by Lt. John L. Worden. The Monitor had just reached Hampton Roads after a precarious voyage from New York City. The ships engaged in a four-hour close-range duel, which resulted in a draw. This combat between two ironclad warships marked a revolution in naval warfare.

In April the Virginia, under Capt. Josiah Tattnall, again challenged the Monitor, but the Union ship declined combat. When General McClellan's advance in the Peninsular campaign forced the Confederates to abandon Norfolk, Tattnall, unable to lighten the Virginia sufficiently for passage up the James River, destroyed her (May, 1862). The Monitor foundered and sank in heavy seas off Cape Hatteras in Dec., 1862.

In 1973 scientists discovered the intact wreck of the Monitor, and the site was subsequently protected by the Monitor National Marine Sanctuary. The steam engine and turret of the Monitor were recovered in 2002 for display with other artifacts at the Mariner's Museum, Newport News, Va.

Any of about 50 species of lizards (genus Varanus, family Varanidae) found in the Old World tropics and subtropics. Most have an elongated head and neck, a heavy body, a long tail, and well-developed legs. The smallest monitor grows to 8 in. (20 cm), but several species (e.g., the Komodo dragon) are very large. The two-banded, or water, monitor (V. salvator) of Southeast Asia grows to 9 ft (2.7 m). The perentie (V. giganteus) of Australia grows to 8 ft (2.4 m). The earless monitor (Lanthanotus borneensis), a rare lizard of Borneo and the only species of the family Lanthanotidae, grows to 16 in. (40 cm) in length.

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