A very large spider web was observed in April 1998. The isolated web covered the vegetation over a distance of appr. 25 m. There were thousands of spiders in the web. Most belonged to Oedothorax retusus (Westring), a few to O. fuscus (Blackwall). The weather was not typical ballooning weather: a heavily clouded sky, some drizzel in the afternoon, a mean temperature of 8° C, and a maximum temperature of 10° C. Probably true “ballooning” did not take place, but the driving force behind the phenomenon must have been the same: an extremely high population density in a grassy bank along a path in this public park in the town of Groningen.