WESTERN BROWARD COUNTY, Fla. -

U.S. Sen. Bill Nelson went python hunting Thursday but returned empty handed.

Nelson participated in the Florida Fish and Wildlife Conservation Commissions' month-long "Python Challenge." Florida wildlife officials say 21 Burmese pythons have been killed so far in a public hunt for the invasive species in the Everglades.

It's unknown how many pythons live in the Everglades. Even experienced hunters have a hard time spotting the snakes in the swamplands.

The Florida Fish and Wildlife Conservation Commission says more than 1,000 people registered for the state's monthlong "Python Challenge." The hunters may find more success if colder temperatures drive the snakes onto sunny surfaces.

The snakes killed since the contest began Saturday will be processed by the University of Florida. The state hopes to apply the data gleaned from the carcasses to management plans for the Everglades.

"They are devouring everything that Mother Nature intended to be in the Everglades," Nelson said prior to leaving.

Nelson returned to a boat ramp at Mile Marker 41 on Alligator Alley about 4 p.m. His office said the "pythons proved elusive in the warm weather."

"What we do is get near the tree islands, get out of the air boats, slog through the marsh grass-- by the way, which is very -- it's razor sharp," said Nelson. "The snakes were not there at the time we were there today."

"And it's just a question of time before one of them gets the endangered Florida panther," said Nelson.

Hunters paid $25 to sign up for the month-long event. Each also had to complete a safety course online. According to FWC, participants are coming from 17 different states to take part.

"If you don't have a trained eye for it -- even if you do like we do -- it's tough," said biologist Shawn Heflick.

Prizes include $1,000 for the longest python caught, and $1,500 for the most pythons killed.

Florida law prohibits possession or sale of the pythons for use as pets.

The competition ends Feb. 10.