Good question, mrcharly. I thought the two were mortal enemies. It would be great to hear someone with knowledge of the subject explain it.
It seemed that the kingsnake had a meal inside it. I wonder if the rattlesnake could somehow be aware of that? But it still seems like a big risk for the rattlesnake.
The other possibility that occurred to me is that the kingsnake was not yet large enough to threaten the rattlesnake, and the rattlesnake could judge its size.
Maybe I should pose the question to a herpetologist from one of the local universities...
- Woodsorrel
I'm a whole lot better than a herpetologist, I'm an ophiologist and my specialist area is Vipers and Elapids. Sadly though, there isn't any solid data to go off. The way they were moving and the environment they were in, including weather conditions and time of day and temperature, also an examination of the surrounding area for other animals and snakes would go some way in helping, but the only thing that would clinch a good explanation is how they were moving and their tongue activity.
A snake would not be interested in another snakes swallowed meal. Kingsnakes do eat other snakes including rattlers, but if it already had a meal in it, then that would rule out that option too. If the king had just killed and swallowed the prey and was still in that area, then the rattler could just have been following the scent trail of that prey item and came to its last known scent spot which was where the king had eaten it.
Snakes like all other animals are curious, so they investigate movement, especially on a warm day when they are active. They are also drawn to roads as they hold a good temperature long after other areas have cooled, so they could have been topping up energy depending on the temperature and time of day. Could just be coincidence. It happens a lot.