Motmot is an island formed in 1968 by a volcanic eruption in Lake Wisdom, a large freshwater lake filling the central caldera of Long Island, Papua New Guinea. The progress of biological colonization of the island, which lies about 3 km from the nearest land, was surveyed in 1969, 1971, 1972 and 1973. Motmot erupted repeatedly in 1973, thus interrupting the gradual increase in life there, so the present account describes the progress of colonization up to November 1972, which was our last visit to the island before the 1973 eruption. The flora of Motmot has grown rapidly from one species of mature higher plant in 1969 to fourteen species in 1972. Sedges of the genus Cyperus were by far the most successful plant colonists. From the distribution and composition of the flora it appears likely that most of the plants originated from seeds carried to the island by Black Ducks (Anas superciliosa Gmelin). The invertebrates which had succeeded in colonizing Motmot by 1972 can be roughly grouped as (1) a strand fauna of small beetles, ants and bugs dependent, either directly or indirectly, on the input of organic material from off-island; (2) ants, which were established in fair-sized colonies among vegetation around the crater pond; (3) earwigs and lycosid spiders which by 1972 were found in almost all parts of the island; and (4) staphylinids and collembolans found beneath a hardened algal crust on the margins of the crater pond. The lycosids were present in 1969 while the other organisms appeared in later years. Black Ducks have been nesting on the island since 1969 while swallows (Hirundo tahitica Gmelin) were first noted nesting there in 1971. The series of eruptions in 1973 killed most of the plant community, but had relatively little effect on the invertebrate fauna.