Invasive ants are becoming a more serious problem as more of the insects are being unwittingly shipped around the world, Spanish researchers say. Colonies being built by some of the invasive species in their new habitats that could pose a threat to the environment, infrastructure and human health, they said. Researchers studying the numbers of exotic ants in the Netherlands, the United States and New Zealand say they found far more of these accidental stowaways than had previously been reported, the BBC reported Wednesday. \"Due to their small size, most ants are transported involuntarily in containers and other boxes, together with soil, wood, ornamental plants and fruits etc, on ships or airplanes,\" Veronica Miravete from the University of Girona said. \"The number of ants arriving is very large and 85 percent of the introduced species are able to establish successfully,\" she said. \"This indicates that there are many introduced species that are living around us as of yet undetected.\" The researchers said they estimate more than 700 exotic ant species could have been introduced around the world through trade routes. In Europe aggressive Argentine ants have been out-competing local ant populations, while in the United States an invasion of South American Raspberry crazy ants is causing problems as the ants show a preference for swarming inside electrical equipment and damaging it. \"Once exotic ants establish a new region it is very difficult eradicate them,\" Miravete said. \"There are different methods to prevent alien species, such as pre-border risk assessments, black lists and quarantine inspections,\" she said. \"But especially, we have to observe shipping routes from the regions with the highest probability of leading to introductions.\"