Horseshoe crabs are a species of marine arthropod that have existed for around 450 million years – but for over four decades, the creatures have also played a crucial role in human health.

The animals’ bright blue blood contains Limulus Amebocyte Lysate (LAL), a substance used by pharmaceutical companies the world over for bacterial endotoxin testing. 

Horseshoe crabs are the only natural source of LAL and are heavily relied upon by the pharmaceutical industry; over 500,000 are captured and bled every year. While LAL’s life-saving properties have made it a vital resource for drug and medical device companies, conservationists say the industry’s demand for horseshoe crabs is threatening their survival – and argue that with a synthetic alternative now available, bleeding the prehistoric creatures can no longer be justified.

Horseshoe crabs used for endotoxin testing in the US are harvested from the East Coast and drained of up to a third of their blood. Though the most of the animals are returned to the water after being bled, they don’t always survive.

Responsibility for animal welfare in the pharmaceutical industry is referred to as the three Rs: reducing the number of animals used, refining studies to minimise their impact on animals, and replacing animal experiments with alternatives wherever possible. In their continued reliance on LAL, Phelan says, drugmakers are failing to adhere to these principles.