Mudlarks would search the muddy shores of the River Thames at low tide for anything that could be sold; and sometimes, when occasion arose, pilfering from river traffic. By at least the late 18th century people dwelling near the river could scrape a subsistence living this way. Mudlarks were usually either youngsters aged between eight and fifteen, or the robust elderly; and though most mudlarks were male, girls and women were also scavengers.
Becoming a mudlark was usually a choice dictated by poverty and lack of skills. Work conditions were filthy and uncomfortable, as excrement and waste would wash onto the shores from the raw sewage and sometimes also the corpses of humans, cats and dogs. Mudlarks would often get cuts from broken glass left on the shore. The income generated was seldom more than meagre; but mudlarks had a degree of independence, since (subject to tides) the hours they worked were entirely at their own discretion and they also kept everything they made as a result of their own labour.
Mayhew in his book, London Labour and the London Poor; Extra Volume, 1851, provides a detailed description of this category, and in a later edition of the same work includes the "Narrative of a Mudlark", an interview with a thirteen-year-old boy.
Although in 1904 a person could still claim "mudlark" as his occupation, it seems to have been no longer viewed as an acceptable or lawful pursuit. By 1936 the word is used merely to describe swimsuited London schoolchildren earning pocket money during the summer holidays by begging passers-by to throw coins into the Thames mud, which they then chased, to the amusement of the onlookers.
More recently, metal-detectorists searching the foreshore for historic artefacts have described themselves as "mudlarks".
- The word was used in the late 18th century as a slang expression for a pig.
- Poor Jack, novel by Frederick Marryat, 1842. In his novel Marryat, who was himself a seaman before he turned to writing, vividly describes the unlikely rise of a fictional mudlark, Thomas Saunders, to the position of river pilot. The book contains many scenes descriptive of the typical mudlark's life, and also suggests that some adult mudlarks were involved in fencing items of cargo stolen and passed to them by crew.
- A mudlark is also a term, used in Sussex dialect for a fisherman from Rye.
- The Copper Treasure - a 1998 book for teenagers by Melvin Burgess describing three 19th century mudlarks and their struggle to successfully transport a roll of stolen copper.
- The Mudlark – a 1950 British film about a young street boy whose contact with Queen Victoria plays a part in bringing her back to public life after her lengthy mourning for Prince Albert.
- In Neal Stephenson's The Baroque Cycle, one of the lead characters, Jack Shaftoe, begins life as a mudlark.
- Mudlark by John Sedden (Puffin 2005) is a thriller set in Portsmouth in the First World War in which two mudlarks find a human skull in the mud of Portsmouth Harbour, beginning a chain of tragi-comic events.
- Society of Thames Mudlarks - A modern organisation founded in 1980 the Society of Thames Mudlarks, has a special licence issued by the Port of London Authority for its members to search the Thames mud for treasure and historical artifacts and report their finds to the Museum of London. In 2009 one of the founder members, Tony Pilson, donated a collection of over two and a half thousand buttons dating from the 14th to the late 19th century, which he had collected along the Thames foreshore.
- The television show Mud Men follows Johnny Vaughan as he teams up with Steve Brooker to go mudlarking along the Thames foreshore.
- The Faerie Ring, a book by Kiki Hamilton also makes a few references to mudlarks.
- Mudlarks, a 2014 PC mystery/paranormal adventure game by Cloak and Dagger Games, features mudlarks and mudlarking prominently in the storyline.
- Oxford English Dictionary. Third edition, March 2003; online version March 2011: According to the Oxford English Dictionary, first published use of the word was in 1785 as a slang term meaning 'a hog'. The dictionary speculates its origin may have been a humorous variation on 'skylark'. By 1796 the word was also being used to describe 'Men and boys ... who prowl about, and watch under the ships when the tide will permit.'
- Henry Mayhew, London Labour and the London Poor; Extra Volume 1851: "Their practice is to get between the barges, and one of them lifting the other up will knock lumps of coal into the mud, which they pick up afterwards; or if a barge is ladened with iron, one will get into it and throw iron out to the other, and watch an opportunity to carry away the plunder in bags to the nearest marine-storeshop."
- Oxford English Dictionary, 1989 edition:"1796 P. COLQUHOUN, Police of Metropolis vol. iii. p.60 'Men and boys, known by the name of Mud-larks, who prowl about, and watch under the ships when the tide will permit.'"
- Henry Mayhew, London Labour and the London Poor; Extra Volume 1861
- The Times, Friday, Mar 11, 1904; pg. 11; Issue 37339; col F, The Police Courts: a 21-year-old man, Robert Harold, "describing himself as a mudlark", was convicted and sentenced to one month in prison for unlawful possession of a length of chain he had dug out from the Thames foreshore, despite the police being unable to cite any owner for the chain.
- The Times, Friday, Sep 04, 1936; pg. 15; Issue 47471; col D "Coppers In The Mud: A Thames Pastime"
- Oxford English Dictionary, 1989 edition: 1785 F. GROSE, Classical Dictionary of the Vulgar Tongue, 'Mud lark, a hog'".
- Arscott 2006
- National Geographic: River Thames "Mudlarks" Dig Up Medieval Toys (2004)