worm being "attacked"by invertebrate

worm being

Observation - worm being "attacked"by invertebrate - UK and Ireland. Description: An invertebrate of some sort, possibly a beetle larva, had attached itself to a living worm and was dragging it around for some time. Eventually it released the worm and disappeared but the worm subsequently died. I wonder what was going on?

An invertebrate of some sort, possibly a beetle larva, had attached itself to a living worm and was dragging it around for some time. Eventually it released the worm and disappeared but the worm subsequently died. I wonder what was going on?