Tadpole Shrimp

Triops cancriformis

- Tadpole Shrimp (Triops). Copyright Neil Phillips

Description/identification

‘A living fossil’ – believed to be the oldest surviving animal species in the world – the tadpole shrimp’s appearance has remained almost unchanged for the last 220 million years! Tadpole Shrimps look like miniature horseshoe crabs. It’s hard to mistake them for anything else! The hard carapace protects them from predators in their temporary pond habitats. They can grow up to about 10cm in length, have a red brown colour, two long ‘tails’, and many legs and long feelers to help them find food in their muddy homes. Close up you can see where they get their name. Triops can be translated as 3-eyed – two compound eyes and a central primitive light sensing organ (their third eye).

Habitat

Tadpole shrimp are a specialist of temporary ponds. Not only are they capable of surviving long drought periods, they actually needs ponds to dry out in between years in order to trigger hatching. Populations of predators and competitors can’t build up in temporary ponds the way they can in permanent ponds. Along with the fresh rainwater and turnover of nutrients in the traditionally grazed sites where they occur, makes just the right cocktail for them to thrive.

Life Cycle

These amazing animals have an extraordinary lifecycle. During the months their temporary ponds remain dry their eggs lay dormant waiting for the rains. Once their ponds fill, they burst forth, quickly growing and breeding before their ponds once more dry out and their short lives come to a close. Their eggs are incredibly well adapted to their conditions. Only a proportion of eggs will hatch each time a pond fills with water. Some eggs will remain dormant for many years, in some cases decades. This means that if a pond dries out before the adults have had time to breed all is not lost and the cycle can continue the next time the pond fills.

Distribution and threats

Our native Tadpole Shrimp is currently found in only two locations, the New Forest in Southern England and near the Solway Firth in Scotland. One of Britain’s most endangered animals, this species is so rare, and its populations so isolated from each other, that there is a very high risk it will become extinct without our help. They are a protected species and require a licence from Natural England in order to net them, handle them or remove them or their eggs from the site.

The biggest threats to this species are loss of grazing on its ponds, which is essential to maintain the right habitat, and climate change which could make the handful of remaining ponds unsuitable for the tadpole shrimp’s survival.