In the area of investigation 50 species of Pteromalidae (2 Spalangiinae, 19 Miscogasterinae 4 Tridyminae and 25 Pteromalinae) were caught. The species which are most numerous and ecologically most important are Cyrtogaster vulgaris Asaphes vulgaris and Meraporus graminicola. Endemic species are missing. Urolepis maritima is the only species which lives at salt pools.Only a few species live in the pastured salt marshes: in the lower area of Puccinellia maritima there is only I indigenous species, in the area of Festuca rubra littoralis there are 6. Polders and terpen on the marsh islands are populated by the same species of Pteromalidae. The marsh islands resemble the salt marshes on the mainland in their combination of species. The development from salt marsh to polder causes some changes in the density of species and specimens. A rapid course of successions results from the building of dikes and reserves. The number of Pteromalid species rises from 6 in pastured salt marshes to 30 in polders or salt marsh reserves. At the same time the number of specimens increases.Most species have several generations. Most of them parasitise Diptera undermining plant tissue. The existence of monophagous Pteromalids could not be proven with certainty. The females fly up but then are drifted away by winds. After having drifted for 30 to 40 km over the sea they are still able to distinguish yellow and blue traps on light ships. When settling in a new area they have a high coincidence with their hosts.The adult Pteromalids are active only in the day-time and above a certain threshold of temperature which varies according to the particular season. This threshold can easily be raised or lowered experimentally. By adjusting the threshold the daily activity is limited to the warmest hours of the day. Even in periods of continuously warm weather the animals are active for about 6 hours a day only. Activity patterns with 2 peaks (bigeminus) were not found in the field.Pteromalid adults flooded for a short time were damaged to such an extent that they could hardly move after the water had run off. Higher temperatures of water accelerate the development of irreversible damage. Flooded specimens are lighter than water and dry to reach the surface. After a few hours they die. In the open they are drifted away by high tides. The areas depopulated after such a high tide are quickly populated again by new specimens.Adaptation of adult Pteromalids to specific factors of the tidal region could not be found. Pteromalids living in this area are able to survive because 1. they do not hibernate as adults; 2. they parasitise hosts living safely in plants; 3. they hatch from their hosts in a metachronous fashion. 4. they fill up population gaps quickly. This shows that despite their high abundance in the tidal regions Pteromalids have not adapted themselves to tidal factors.