Damselflies are similar to dragonflies, but they are smaller, have slimmer bodies, and most species fold the wings along the body when resting. An ancient group, damselflies have existed since at least the Lower Permian Period, and are found on every continent except Antarctica. All damselflies are predatory; both nymphs and adults eat other insects. The nymphs are aquatic, with different species living in a variety of freshwater habitats including acid bogs, ponds, lakes and rivers. Their presence on a body of water indicates that it is relatively unpolluted, but their dependence on freshwater makes them vulnerable to damage to their wetland habitats. Damselflies sometimes provide the subject for personal jewelry such as brooches.