C. tenellum is an Atlanto-West-Mediterranean species. Its range towards the north extends to the Netherlands and NW Germany where it is limited by the North Sea. In Great Britain it is restricted to the southern and south-western parts of England. The northernmost breeding sites exceed 53°15’N in England (M. MERRITT, N.W. MOORE &B.C.EVERSHAM, 1996 .Atlas of the dragonflies of Britain and Ireland, HMSO, London) and in the Netherlands (M. WASSCHER, R KETELAAR, M. VAN DER WEIDE, A. STROO, V. KALKMAN, N. DINGEMANSE, H, INBERG & I. TIELEMAN, 1995. Verspreidingsgegevens van de Nederlandse libellen. European Invertebrate Survey, Leiden), and 53°30’N in Germany (C. LUNAU, 1939, Sc hr. naturw. Ver Schlesw.-Holsl. 23[l]: 140; E. SCHMIDT, 1975, Ber. Ver. Nat. Heimat nalurh. Mus. Liibeck 13/14: 25-43; K, RETTICH, 1989, Beilr. Vogel-Insektenwelt Ostfriesl. 36: 14-21; R. SCHMID, 1995. Die Libellenfauna Ostfrieslands, Ostfriesische Landschaft, Aurich). ln the northern area C. tenellum is confined to fens. Sphagnum-bogs, moorland ditches, and pools in sand pits with a distinct flow of ground water. Since this kind of habitat is not rare in the Netherlands and in NW Germany, the species is rather widespread there and locally abundant. The phenology in this area has thoroughly been studied in the Lower Rhine region, in particular at the „Löschteich Orvennsbahn“ (51°H’N; 6°05’E), and the main flight period turned out to be from early July to late August (U.KRÜNER, 19&6, Libellula 5[V4]: 85- -94; 1989a, Verh. westd. Ent. Tag 1988: 133-140; 1989b, Decheniana 142: 74-82; R. JODICKE, U. KRONER, G. SENNERT & J.T. HERMANS, 1989, Libellula 8[ 1/2]; 1-106); extraordinary phenological dates are discussed below. In 1995 I started to observe an abundant population of C. lenellum at the Diana lakes in Lower Saxony (52°55’N; 8°09’E). In the first year 1 made no systematic phenological investigation, but I recorded the last male on 19 September. 1996 and 1997 I daily looked for the last individuals on wings and recorded a continuous presence until 30 and 19 September, respectively. The first emergence at the Diana lakes was observed on 2 June 1997. In the same year, C. tenellum already emerged on 29 May from the nearby ,3örstel“ (52°37’N; 7°43’E). In 1998, fully mature specimens have been recorded at the latter habitat on 31 May. Due to the cold and wet wheather which preceded the record, their emergence most probably had started in a hot period during mid May which lasted until 19 May.