Scientists have witnessed how death spreads through a living creature like a wave, each cell dying one after another until the entire organism is deceased.
A British team captured the final moments a tiny, transparent ground worm's life by tracking a blue fluorescence molecule that travels through the organism's cells as it dies.
While scientists understand many of the processes that causes individual cells to die, far less is known about the chain of events that propagate death throughout an entire animal.
As the biological mechanisms of death in worms are similar to those in mammals, the researchers believe the worm could prove a useful model for understanding death in humans.
University College London ageing researcher David Gems and his team have identified the chemical pathway of self-destruction that moves through worms during their final demise.
Peering through a microscope the researchers could watch the death sequence unfold because it was accompanied by a molecule, believed to be anthranilic acid, which gave off a blue hue as it moved from dying cell to dying cell.
"It's like a blue Grim Reaper, tracking death as it spreads throughout the organism until all life is extinguished," said Professor Gems from UCL's Institute of Healthy Ageing.
The identification of the blue death marker led the team to discover the role calcium played in generating the wave of cell death.
This chemical chain reaction then prompted a break down of cell components and a build-up of molecular debris, which ultimately killed the whole organism.
"We found that when we blocked this pathway, we could delay death induced by a stress such as infection, but we couldn't slow death from old age," he said.
It has been predicted that preventing major age-related diseases such as heart disease and cancer would only increase longevity in humans by a small amount.
"This is because multiple pathologies act in parallel to increase age-related mortality," wrote the authors, whose findings were published in the journal PLoS Biology.