Pleidae

Pleidae, the pygmy backswimmers, is a family of aquatic insects in the order Hemiptera (infraorder Nepomorpha, or "true water bugs"). There are 37 species in three genera, distributed across most of the world, except the polar regions and remote oceanic islands.

Pleidae belong to the Tripartita which contains the more advanced lineages of true water bugs, and are closely related to the true backswimmers (Notonectidae), but closer still to the Helotrephidae, another family of tiny Nepomorpha, which usually swim upside-down and, like the Pleidae, have a sensory organ in the center of the clypeus. Either the pygmy backswimmers are united with the Helotrephidae in the superfamily Pleoidea, or these two and the true backswimmers are placed in a single superfamily Notonectoidea.

Distribution

In Europe there is a single species, Plea minutissima, widely found in that continent. Plea species occur in the Old World, while Neoplea is found in the Americas. Paraplea can be found in all warmer parts of Earth, including Australia, where three species occur. Given their inability to fly well – if they can fly at all –, it is not surprising that the Pleidae do not have as many endemic island taxa as some other Heteroptera (true bugs). Only five species are known from the entire Malesian archipelago for example. Neoplea apopkana has been introduced to the Hawaiian Islands in Polynesia. One species, originally native to South Asia and Southeast Asia, was found in aquaria in New Zealand. In 2006, Paraplea puella was found to be introduced to Guam in Micronesia. Like in the preceding case, this originally American species was probably accidentally introduced with aquarium plants.