The bootlace worm, a ribbon of black slime found tangled on North Sea beaches, can stretch to more than 55 metres (longer than a blue whale), making it arguably the longest animal on Earth, and its skin secretes a neurotoxin that killed cockroaches and crabs after laboratory injection

A 55-metre specimen stranded on a Scottish beach in 1864 made the bootlace worm a contender for the longest animal on Earth. In 2018, Swedish researchers found its mucus contains a peptide neurotoxin that paralyses crabs and kills cockroaches, while leaving mammalian nerves largely untouched.