A solarium is an earthen structure constructed by certain members of the Formicidae for the purpose of brood incubation. Solaria are usually dome-shaped and fashioned from a paper-thin layer of soil, connected to the main nest by way of subterranean runs.
Tapinoma erraticum is an example of a solaria-constructing species whose skill at so doing was noted by Horace Donisthorpe in the early 20th Century in his book British Ants, their Life Histories and Classification.