Out of selfishness, I would prefer the answer to be "No, it doesn't prevent suffering to squash the worms instead of leaving them to die," because this would exempt me from compunction about not spending more time to help them. However, I'm curious to hear an honest answer. If worms can suffer meaningfully (my probability is > 0.2 that they can), and if quickly squashing a dying worm would prevent several minutes or hours of severe pain, then I could directly prevent a fair amount of suffering by spending some time walking around to kill them.
A small proportion of the dying worms are actively thrashing about, and these seem fairly obviously to be in pain (if worms can indeed feel pain of the type we care about). But most lie relatively still, seemingly unable to finish a journey across the pavement that they tried to begin. However, they seem to have enough hours of life left in them that I would guess that squishing them is less agonizing than letting them remain as they are.
To quote Jeff Lockwood from the comments of my earlier blog post on this subject:
Because I don't enjoy the process of spending time to crush worms, I would be grateful to discover that they're better off being left alone; but I doubt this is the case. I wonder: Is there a more systematic method that people could use to prevent worms from suffering like this?I’d concur that it is ethically sound to kill a partially crushed worm (there is even some biochemical evidence that worms can suffer, as they possess serotonin and endorphins). They writhe and appear to exhibit behaviors that a compassionate and reasonable person would justifiably conclude are evidence of suffering (the issue being—if you are wrong and the worms aren’t suffering, then nothing has been lost by your action, other than a moment of time and the angst of mistaken empathy, but if you are right, then those who don’t take a second to act compassionately lose a great deal as does the worm). My sense is that it takes a rather long time for a partially crushed worm to die, as its physiology and anatomy are such that death would not follow nearly as quickly as it would for a mammal with a more complex and concentrated set of vital organs.
Thanks for the comments!