Rat snakes are beneficial in the garden and they were probably hunting for prey when they got entangled in the plastic.
I wonder if they were all from the same family?
I copied and pasted the following from Wikipedia;
Behavior:
The Texas rat snake has a voracious appetite, consuming large numbers of rodents and birds, and sometimes lizards and frogs which they subdue with constriction. They are generalists, found in a wide range of habitats from swamps, to forests to grasslands, even in urban areas. They are agile climbers, able to reach bird nests with relative ease. They are often found around farmland, and will sometimes consume fledgeling chickens and eggs, which leads them to be erroneously called the chicken snake. They are known for their attitude, and will typically bite if handled, though their bite is harmless.
More interesting information about the Texas Rat Snake:
http://www.uta.edu/biology/her...
