Study Finds Invasive Ant Species Have Gone Global

May 10, 2018

The majority of ants entering the United States are coming not from their native countries, but from other regions, according to a new U.S. Forest Service study released this week, co-authored by a Morgantown entomologist.

Over the past two centuries, more than 400 insects have invaded the U.S. Some of those include ants. And although they are little, ants can cause big ecological problems worldwide including triggering outbreaks of sap-feeding insects because some non-native ant species keep away parasites.

Some non-native ant species displace native ants, which can cause decline in native plant species that depend on those species for pollination. Some, like the red imported fire ant, are highly venomous.

An international team of researchers looked at more than 70 years of data collected by the U.S. and New Zealand. The data tracked when USDA inspectors found ants at air and maritime ports of entry.

Between 1914 and 1984, ants were found more than 1,400 times at U.S. ports. More than three-quarters of those ant species came from shipments outside their native range.

Andrew Liebhold, a research entomologist with the U.S. Forest Service Northern Research Station in Morgantown, who was a co-author of the study, said that was surprising. The data showed most of the ants intercepted at U.S. ports are African species, but they weren't stowing away with goods from Africa.

"What seems to happens is that these species is they initially invade one part of the world and then those parts of the world basically serve as jumping off points for the rest of the world," he said.

Most U.S. ant invaders, for example, are coming from Latin America.

Leibhold said it's a bit of mystery as to why ants are coming from outside their native range. One reason might be that certain parts of the world are more connected through trade.

As a result, ants, like most other things, may have gone global, he said.

By having a better understanding of what species are coming into U.S. ports and from where, officials may be able to better prevent invasive ants from entering the country. Port officials, for example, could set up more detailed screening protocols for goods coming from certain ant-prone places or encourage more cleaning of certain imports.

Researchers from the University of Lausanne, University of Paris-Sud, the New Zealand Forest Research Institute and Landcare Research also participated. The study was published in the journal, Proceedings of the National Academy of Sciences.