Caecilians (; New Latin for "blind ones") are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics of South and Central America, Africa, and southern Asia. Their diet consists of small subterranean creatures such as earthworms.
All modern caecilians and their closest fossil relatives are grouped as a clade, Apoda, within the larger group Gymnophiona, which also includes more primitive extinct caecilian-like amphibians. The name derives from the Greek words γυμνος (gymnos, naked) and οφις (ophis, snake), as the caecilians were originally thought to be related to snakes. The body is cylindrical dark brown or bluish black in colour. The skin is slimy and bears grooves or ringlike markings.
Caecilians are native to wet, tropical regions of Southeast Asia, India, Bangladesh, Nepal and Sri Lanka, parts of East and West Africa, the Seychelles Islands in the Indian Ocean, Central America, and in northern and eastern South America. In Africa, caecilians are found from Guinea-Bissau (Geotrypetes) to southern Malawi (Scolecomorphus), with an unconfirmed record from eastern Zimbabwe. They have not been recorded from the extensive areas of tropical forest in central Africa. In South America, they extend through subtropical eastern Brazil well into temperate northern Argentina. They can be seen as far south as Buenos Aires, when they are carried by the flood waters of the Paraná River coming from farther north. Their American range extends north to southern Mexico. The northernmost distribution is of the species Ichthyophis sikkimensis of northern India. Ichthyophis is also found in South China and Northern Vietnam. In Southeast Asia, they are found as far east as Java, Borneo, and the southern Philippines, but they have not crossed Wallace's line and are not present in Australia or nearby islands. There are no known caecilians in Madagascar, but their presence in the Seychelles and India has led to speculation on the presence of undiscovered extinct or extant caecilians there.
In 2021, a live specimen of Typhlonectes natans, a caecilian native to Colombia and Venezuela, was collected from a drainage canal in South Florida. It was the only caecilian ever reported in the wild in the United States, and is considered to be an introduction, perhaps from the wildlife trade. Whether a breeding population has been established in the area is unknown.