SEVERAL SHOWS, including Disney?s classic ?Dumbo,? have played upon the notion that elephants are afraid of mice. Some researchers suggest that elephants aren?t terrified of these much smaller creatures but rather are wary of moving near what they can hear but not see.

Biologists affiliated with the Mpala Research Centre in Kenya have now determined that even smaller creatures could keep elephants at bay. In a study published online Sept. 2 in the journal Current Biology, Jacob Goheen and Todd Palmer observed how ants interact with elephants foraging for food in an African savannah.

They found that despite their much larger size, the elephants steered clear of acacia trees that were home to ant swarms, which in turn helped reduce the chances of seeing the savannahs converted to grasslands as a result of foraging.

Major impact

?It really is a David-and-Goliath type of story, where these little ants are up against these huge herbivores, protecting trees and having a major impact on the properties of the ecosystems in which they live,? said study coauthor and University of Florida biologist Palmer in a statement. ?When either tree species had ants on them, the elephants avoided those trees like a kid avoids broccoli.?

Many of the trees in these regions had developed defenses to avoid being eaten, the researchers noted. For example, various species of acacia trees had spiny branches and also contained compounds that made them hard to digest. These built-in defenses did not deter large foragers such as elephants, however, from feasting on the plant mass, which could permanently damage the trees and reduce their presence in the region.

To better understand how the ants could impact the elephants? food choices, the researchers did several tests to determine if the elephants simply preferred acacia trees grown on clayey soil to ant-infested trees grown on sandy soils. They found that if ant-free tree branches from both soils were presented to the elephants, they were devoured regardless of tree species and variety.

Goheen and Palmer attributed the elephants? decision to typically avoid ant-infested trees to ?the tendency of ants to attack areas of thin skin and mucous membranes by biting down and holding fast with their mandible?. Despite their thick dermis,? they noted in their paper, ?elephants are highly sensitive around their eyes and on the inner membranes of their trunks; attack by scores of biting ants probably serves as a strong deterrent.?

Plant-ant symbiosis

A second set of experiments confirmed that when the plant-ant symbiosis was interrupted, over time the damage done by the foraging elephants was significantly more than would have been the case had the ants been present to protect their homes.

?We had solved that part of the mystery?swarming groups of ants that weigh about five milligrams each can and do protect trees from animals that are about a billion times more massive,? Palmer said in a statement.

The ants? symbiotic relationship with the acacia trees of Africa trading protection for shelter, is a marked contrast to the relationship observed between particular species of fungi and ants in the tropical forests of Thailand.

As reported in the Aug. 18 edition of the journal Biology Letters, parasitic fungi infect the brains of ants and divert them from their usual duties. Before the infection kills them, these so-called ?zombie ants? are steered toward ideal breeding grounds and conditions for the fungi to grow before repeating the cycle once more.

E-mail the author at massie@massie.com.