Some snakes worldwide appear to be growing ever larger, and reptile experts believe people may be helping to drive the growth.
A nearly 18-foot-long Burmese python, for example, was recently discovered in the Florida Everglades. It is one of the largest ever pythons found there.
"The maximum size of Burmese pythons in the Florida Everglades has been increasing by 6 inches to a foot a year for the past five to six years," J.D. Willson, assistant professor of biological sciences at the University of Arkansas, told Discovery News, adding that he expects a 20-footer to be found there before long.
As their name suggests, Burmese pythons are not native to Florida. Instead, they are native to Southern and Southeast Asia. Willson explained that they were all the rage in pet stores back in the day.
"From the 70's to the 90's, you could buy baby Burmese pythons in pet stores," he said.
Some escaped, or were released into the wild. The Florida Everglades has turned out to be a good habitat for them -- at least initially -- and their population has been established there since at least the year 2000.
Willson said that, unlike mammals, snakes continue to grow as they age. He thinks that the recently caught python in the Everglades was at least 10 years old.
Two other invasive species, African rocky pythons and non-native boa constrictors, have also been found at huge sizes in Florida. Boa constrictors have also established a breeding population in Puerto Rico.
Non-native boas can exceed 10 feet and 75 pounds, according to U.S. Geological Survey director Marcia McNutt. She said island ecosystems are particularly vulnerable to snake invasions.
Very large brown tree snakes have been found on yet another island, Guam. Willson explained that brown tree snakes probably were accidentally introduced to the island during World War II, when they might have stowed away in cargo.
The trend seems to be that non-native snakes grow very large at first and then become smaller as their food supply diminishes. Brown tree snakes already have driven many native birds and lizards on Guam to extinction.
Climate change may also be contributing to snake sizes.
University of Illinois researcher Patrick Weatherhead and colleagues recently found that warming temperatures benefit ratsnakes in Canada, Illinois and Texas. Weatherhead expects ratsnakes to become more active at night and to expand their ranges northward.