Comatose iguanas have been dropping from the trees and pythons have frozen to death in their tracks in Florida's unusually harsh winter, wildlife officials said today.

Parts of the Sunshine State saw their second snowfall of the season this weekend, with the extended cold spells killing off a host of tropical intruders, including iguanas, Burmese and African pythons and invasive fish.

State wildlife officials said more than half of the green iguanas, which are native to South America, could have been killed off. "The iguanas up in the trees just got so cold, they kind of went very, very sluggish, and just fell down," said Jenny Tinnell, a biologist with Florida's Fish and Wildlife Conservation Commission.

Residents of south Florida, who have discovered the animals on their patios, have tried to warm them back to life.

Local newspapers, meanwhile, have been warning homeowners not to let their dogs gnaw on iguana corpses, which may be poisonous.

In the Everglades, trackers licensed by the state have discovered the decaying corpses of three African rock pythons, which can reach over 20ft and can kill people. State officials believe up to half of the Burmese pythons have also died, along with large numbers of invasive fish.

The python die-off could be helpful to wildlife officials. The alien constrictors, many of them abandoned pets, have been taking over portions of the Everglades, threatening native species.

Last month, the Obama administration said it was considering a ban on nine species of giant snake.

"The fish and wildlife commission has no problem with nature naturally knocking back those populations," said Tinnell.

But the harsh winter is also harming natives such as the manatee, which is an endangered species. Long periods of cold weaken their immune systems. Officials said about 200 manatee carcasses have washed up on shore since the beginning of the year. Dozens of crocodiles have also died.

The extreme temperatures also prompted a rescue effort last month for endangered sea turtles. Officials plucked more than 4,000 from chilly waters, bathing them in warm salt water to revive them.