Big Headed Ants Dominate Insect World On Kure Atoll -- 26,500 Ants Per Square Meter Found In Some Sections Of The Island

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If the quick density sampling conducted on Green Island yesterday proves to be accurate, big-headed ants (Pheidole megacephala) have overrun the ecosystem on the only permanent land mass within Kure Atoll.

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The density sampling, conducted by entomologist Gordon Nishida and wildlife
biologist Beth Flint (above), recorded on average, an astounding 26,500 ants per square meter at the sample sites.

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Photo Courtesy of Dr. Bastiaan "Bart" Drees

"It's an incredible number," remarked Nishida. "But even more incredible is that our count was done on surface ants only. Many other ants in a colony, including the queen, live deeper underground. We have no idea what their numbers might be here."

Non-native ants are one of the few animals that can quickly and completely break an ecosystem. "They're ecosystem- busters," remarked Flint. "Ants are incredibly effective and efficient predators and have few limits on their diet. They'll eat anything that doesn't have a defense. And because on Kure, these alien ants have no natural predators to control their population, as long as they can find food, their colonies will probably continue to grow."

"Big-headed ants are known exterminators of other insects," said Nishida. "Their strong presence on the island may explain why it was so difficult to find very many insects on the island. Native insects would have no defenses against these ants, therefore would be easy prey and their astonishing numbers here would probably affect even non-native species."

To complicate matters, these alien ants feed on the nectar of another introduced insect, a scale that is also very common on island. The scale insect breeds on an aggressive, introduced plant called Verbesina encilioides (a member of the aster or daisy family), which has also overrun the island. As the plant continues to spread on the island, so does the
scale population, which assists in the explosion of ants. "The large scale population seems to be killing the Verbesina, which is a plus, but the scales have also moved onto the native naupaka (Scaevola), leaving the typical blackening caused by a fungus growing on the "honeydew" produced by the scales. The ants collect the honeydew from the scales. In return for the honeydew, the ants protect the scales from parasites and predators, creating a powerful partnership," explained Nishida.

"Typically, when ants move into an ecosystem, many native insects become at risk. I suspect that's what happened here. This is also what is happening in the main Hawaiian Islands. Because the ecosystems in the main islands are more complex, the impacts to native species are often harder to understand," explained Nishida. "For this reason, it's important that we learn about what's happening at places like Kure. These northwestern islands and their limited ecosystems hold many lessons that can be applied to natural resource management in the lower islands.

"These relationships are complicated," said Nishida, even in a relatively simple ecosystem like the one on Kure. In my opinion, the numbers of ants we found through our brief sampling warrants a closer look at the situation.

In short, Nishida believes that comprehensive research on the ant problem is needed. "Someone should study the problem more closely, and the State of Hawaii Department of Land and Natural Resources needs funding to be able to make this kind of research happen. Without it, they won't be able to determine the best course of action to control the ant explosion or understand why the ant numbers are so high or what their impact may be. Kure is an important place for wildlife, particularly seabirds, but the ants could really change that."

"Especially given the remote location of the Atoll, the State DLNR has been doing a great job in increasing suitable habitat for ground-breeding seabirds and other wildlife," said Flint, who has been working in the
Northwestern Hawaiian Islands for the 20 years. "But all their good work could be greatly compromised if the ant situation isn't brought under control. It's a real concern."

According to Flint, on Midway Atoll, biologists have instituted an ant control program. They've also undertaken steps to control Verbesina on the Atoll. "Perhaps Midway will have some answers for what can be done on Kure," said Flint.

"At virtually every place we've been so far on this expedition, alien insects dominate the insect world, with a small number of insect species extremely prevalent," explained Nishida. "On Kure, the ants are doing the whole job of what groups of different kinds of insects would do in an ecosystem to keep it healthy. The balance of the system is, in my opinion, out of whack."

The Hawaii Department of Land and Natural Resources manages Kure Atoll as a wildlife sanctuary. Due to limited funds, management activities on the island are also limited to a few work trips per year, at most.

The density sampling wasn't a planned work objective for the pair of scientists. The idea occurred to them quickly after arriving on island however, when it became obvious to them that the ants were everywhere, and in noticeable numbers. Every item on the ground, whether rock, plants, or debris were teeming with ants.

The sampling was done creatively, using film canisters and a firm piece of plastic to collect even samples of surface sand at 12 different spots on the island. The sand and insects found in the sand were then placed in collection "kill" jars so Nishida could conduct a count of the ants. Each canister measures 683 square millimeters. This figure was then used to calculate what the density of ants would be over a square meter.

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