Many alien insects enter the United States as hitchhikers on imported plants. But how many live long and prosper?

Although conventional thinking says the answer lies in the numbers of insects and how many times they enter, new UC Davis findings published recently online in the Proceedings of the National Academy of Sciences suggest that opportunity alone is no guarantee of a successful invasion.

In a study of accidentally imported ants in the U.S., 12 percent of the species took up residence here. The key to their success was finding nesting sites like those they left behind.

"This investigation helps us better understand which characteristics make organisms successful invaders," said Philip Ward, a UC Davis professor of entomology.

The new findings arose from studies by Ward and a postdoctoral student, Andrew Suarez, who is now a professor in the entomology and animal biology departments at the University of Illinois at Urbana-Champaign.

Suarez discovered a gold mine of untapped ant history in the Smithsonian Institution's National Museum of Natural History: samples of ants intercepted by the U.S. Department of Agriculture from 1927 to 1985 at ports of entry around the country. Ward and Suarez spent years identifying 232 different species from 394 samples. Then they teamed with David Holway, a professor of biology at UC San Diego, to analyze their discoveries.