Argentine ant distribution map, Haleakala National Park, Maui, Hawaii
Hawaii's native animals, including its pollinators, evolved in isolation, 2,000 miles from the nearest continent, without ants.
As a result, insect pollinators in Hawaii are extremely vulnerable to predation by aggressive, immigrant, alien ant species. Immigrant ants have reduced or eliminated native insect pollinators in most low elevation areas of Hawaii; higher elevation ecosystems remain more intact.
However, the Argentine ant, a species capable of invading alpine elevations, is spreading throughout Haleakala National Park, one of the state's most intact ecosystems. The species has also proven itself a pest in California and other parts of the world.
Over the past 15 years, research has shown that the Argentine ant at Haleakala National Park is expanding its range at a rate of over 50 yards per year. Because queens are unable to fly, the spread of this species is relatively slow.
Wherever this tiny, voracious predator spreads, however, it reduces and can even halt reproduction of pollinators such as native bees and moths. The ant now occupies about five percent of the park and has the potential to occupy up to half of the area.
Argentine ant encroachment is ominous for all insect-pollinated native plants. The most alarming threat involves the famous Haleakala silversword, a federally-listed threatened species that grows only within the ant's potential range. This giant, silvery subalpine plant grows for 30 to 50 years, then sends up a six-foot tall flowering stalk, sets seed, and dies. Cross-pollination is essential for seed set, but for this plant it is critical for its survival.
Silversword-pollinator relationships are currently being studied. Strategies for containment or local eradication of the Argentine ant are also being explored with preliminary success.
Careful chemical control may prove successful in containing the ants and saving the yellow-faced bees that the threatened silverswords depend on for pollination.
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