1.The Bärenhöhle, one of the ten caves situated in the episodically water-bearing valley of the Lone (Swabian Jura), serves as summer quarters for the total of ten species of Trichoptera, most of which are Micropterna nycterobia and Stenophylax permistus. 2.Counts carried out in this cave from 1967-1972 and observations of flood and dry-periods of the Lone during the same years make evident that the number of Trichoptera flying into the cave seems to depend in a large measure on the seasonal activity of the creek: a steady flow of water makes the undisturbed development of larvae possible and results in high numbers of individuals entering by air, while intermittent water-flow disturbs the development of the larvae and results in few individuals entering. 3.Such factors as darkness, humidity, and temperature which cause or favour the active entrance by air of Trichoptera into the cave as well as the “diapause” taking place in the subterranean region are considered. 4.Dynamically climatized caves or caves which are too small are rarely occupied by Trichoptera; they evidently prefer larger caves with climatically balanced regions (comparatively low temperatures and high atmospheric moisture) not too far from the entrance. 5.Trichoptera start flying into the Bärenhöhle generally in May; the highest number of individuals and copulating couples may be found as early as July. They start flying out by the end of July or in August/September, the last of them leaving the cave generally in September or October. 6.Two attempts at marking (on 28th June all Trichoptera to be found in the cave were marked with black ink, on 4th July all yet unmarked with red ink) gave better evidence of their disposition and time of copulation as well as of the number of arriving unmarked and departing marked specimens. 7.The Trichoptera marked with black ink stayed in the cave for a maximum of 85 days, the ones marked with red ink for a maximum of 79 days. Food intake was not observed during this period, and there was no indication of the insects’ leaving the cave during their diapause. 8.Trichoptera are characterized by a remarkably long time of copulation: a specimen marked twice was in copula for 22 days, and before copulation it had been in the cave for 49 days.