This winter egg is produced after mating. Male water-fleas only develop when conditions become unfavourable (e.g. drought or cold). These special resistant eggs have a protective wall that consists of the remains of the brood pouch of the female.

The egg can lay dormant for months until the conditions become better. In some species this time capsule is thickened. These eggs can float and can even be transported by the wind so new ponds can be inhabited.