Several types of insect live on the sea shore, but only five species are truly marine.
Pond Skaters and the Ocean Striders
All Pond Skaters can walk on water. They spread their weight with long legs and rely on surface tension to keep them afloat. Most live on fresh and brackish waters, but five species of the genus Halobates (Ocean Striders) live on the surface of tropical oceans. They are the only truly marine insects. Unable to enter the water, they lay their eggs on flotsam and feed on anything that floats to the surface, such as dead jellyfish and fish eggs. They inject digestive juices into the food and then suck up the nutrients.
Other Insects found on Sea Shores
- Intertidal Rove Beetles
Bledius spectabilis is a small predatory beetle that builds burrows in sand. It cannot survive without air, so it is only active when the tide is out. When the tide is in it retreats to its hole and the narrow opening (2mm) does not allow any water in.
- Seaweed Flies
These insects are attracted by the smell of rotting seaweed that is deposited on the shore. They lay their eggs, and the maggots gorge on the compost. Adults are short-lived, their job is to find a mate and then search out the next pile of rotting weed.
- Bristletails
Petrobius maritimus (the Shore Bristletail) is found all round the British coastline. This very primitive wingless insect (closely related to the Silverfish and Firebrats) cannot survive immersion in water, so it must hide in rock crevices when the tide is in. It feeds on detritus (rubbish!) when the tide is out. Bristletails can run quite fast, and if threatened they can jump a bit.
- Springtails
Anurida maritima (the Rock Springtail) is also common on British shores. It is a very small blue-grey insect without wings. Must springtails have a special jumping organ, called the furcula, which allows them to jump spectacularly. This organ has been lost in A.maritima, and the best they can do is to crawl over the rocks or float on the surface of rock pools.
- Snail Bees
Osmia aurulenta is found around the high tide mark of many European shores, and like most bees it feeds on the nectar and pollen. The name comes from the fact that but it nests in empty ‘snail’ shells that have been washed up, restricting its habitat to the land near the upper shore.
Insects Underwater
Many species of insect have larvae that have gills and live in freshwater, but none can tolerate the sea. Adult insects that live underwater still breathe air, usually carried down with them from the surface. It is curious, given the enormous diversity seen among the insects, that none is known to live in the sea.
Other articles by John Blatchford
