Abstract: Ergatoid (= permanently wingless) queens do not disperse individually from their natal colonies, instead they walk with nestmate workers to new nesting sites during the fission of existing colonies. Very few observations of dependent colony foundation are available, and it must often be studied with indirect data. Thirty-five colonies of Monomorium algiricum (Bernard, 1955) were excavated at different times of the year. New sexuals (ergatoid queens and males) were found during a short period at the end of summer. Dissection of spermathecae in 331 queens revealed that new gynes mate soon after emergence. Ovarian activity was assessed to distinguish between "old" and newly mated queens. Both monogynous and polygynous colonies were found throughout the year; queens in the latter were less fecund. Sexuals were not produced in some polygynous colonies. The life history of M. algiricum is complex due to interactions between extreme seasonality (no foraging and no egg-laying during six months of the year), coexistence between "old" and newly mated ergatoid queens, and the irregularity inherent to colony fission.