A ballooning population of invasive green iguanas on Grand Cayman has become so alarming that the U.K. Caribbean territory has launched a pilot program to figure out how best to fight reptiles that began as escapees from the pet trade.

Fred Burton, manager of the terrestrial resources unit at the Cayman Islands' environment department, said Wednesday that 18 contracted hunters are using air rifles and trained dogs to kill some two tons of green iguanas a day during this month's study.

Officials are using the hunt to get information on what kind of large-scale management operation is needed.

The scope of the invasion on the 22-mile-long (35-kilometer-long) island will require such a plan to beat back the reptiles, Burton said. Their population is believed to be doubling every 1½ years.

"We're expecting a half a million at the next census in August," Burton told The Associated Press. "The numbers are compounding. It's a little shocking, to say the least."

Adults can grow to be several feet (more than a meter) long. With their voracious appetite, the herbivores are taking a big toll on native plants. Burton said there is evidence suggesting that green iguanas are also raiding bird nests.

"If the population is allowed to expand we could see wholescale ecosystem change," he said.

For now, the two smaller islands in the three-island chain have small populations of green iguanas. Grand Cayman, the territory's main island, is overrun.

Introduced populations of green iguanas, which are native to Central and South America, are also considered scourges in Florida, Puerto Rico and other regional islands.