Invasive ant Tapinoma melanocephalum (Hymenoptera: Formicidae): A rare guest or increasingly common indoor pest in Europe?

The ghost ant (GA), Tapinoma melanocephalum (Fabricius, 1793), is one of the most common invasive species of ants (Hymenoptera: Formicidae) in the world. While in its native tropical region it is both an ordinary indoor and outdoor pest, it occurs only indoors in the temperate zone, where increasingly more records of this species have been published since 1887. In this study, the current distribution of GA in Europe, including the new records published since Wetterer (2009), is reviewed. Furthermore, we report the first record of GA in the Czech Republic, where a large colony of GA was discovered in a block of flats in České Budějovice in 2014, and present a case study of its eradication. The revised distribution of GA shows that despite previous concerns about the threats posed by this new pest only three other European countries (including Czech Republic) reported the presence of this species after 2009. Although GA is currently documented as occurring in 18 European countries, which were invaded mainly after 1990, there is only a single (or dubious) record for ten of these countries. Abundance of workers was monitored in two flats in an infested building using traps baited with yolk-honey and GA were subsequently eradicated with imidacloprid (0.01% w/w). The pre-treatment revealed abundances that ranged up to 524 workers per trap (mean = 99, S.D. = 142, 80% of baits occupied). Despite the initial success of the treatment (no ants observed after 3 weeks), monitoring of the building a year later revealed it was still infested with GA and in a similar rate. We suggest alternative methods of eradicating GA in the temperate zone based on studies carried out in the tropics. Our study indicates the difficulty of eradicating the species from buildings when its colony is already established. Furthermore, it highlights the bias in the discovery-probability of GA as a household pest probably due to the species cryptic appearance and lack of attention to it outside of the scientific community.