Preview: Prof. Dr. Kazuki Tsuji, Department of Agro-Environmental Sciences, Faculty of Agriculture, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan. E-mail: tsujik@agr.u-ryukyu.ac.jp Myrmecol. News 13: 131-132 (online 22 March 2010) Issn 1994-4136 (print), Issn 1997-3500 (online) Received 1 November 2009; revision received 12 January 2010; accepted 12 January 2010 Are all ants aggressive? Ants are generally believed to be aggressive animals whose population is structured into many mutually hostile colonies by fierce aggression toward aliens (e.g., Levings & Traniello 1981). Therefore, unicoloniality – in which a population seemingly becomes a single, spatially large-scale, polydomous-polygynous colony in which intraspecific aggression is absent, as often seen in invasive species such as the Argentine ant and some indigenous species – had been regarded as an exceptional phenomenon. Some researchers even consider that unicoloniality of invasive ants is a maladaptive trait caused by anthropogenic events such as a genetic bottleneck upon introduction to a…