A key to European species of Hyposoter Förster, 1869 (Ichneumonidae: Campopleginae) with descriptions of 18 new species, and notes on all included species Author Galsworthy, Anthony 0009-0009-6612-9847 acgalsworthy@btopenworld.com Author Shaw, Mark R. 0000-0002-6651-8801 markshaw1945@gmail.com Author Haraldseide, Håkon 0009-0009-6612-9847 acgalsworthy@btopenworld.com text Zootaxa 2023 2023-05-18 5290 1 1 73 http://dx.doi.org/10.11646/zootaxa.5290.1.1 journal article 53361 10.11646/zootaxa.5290.1.1 36037514-64e6-4cde-88f9-583b4b9d8bf1 1175-5326 7959256 FD54D381-F123-4958-A03E-6CA71E02D06A Hyposoter caudator Horstmann, 2008 Hyposoter caudator Horstmann, 2008 : holotype ♀ in NMBE . We have seen both the holotype and a female paratype in NMS. Very similar to H. notatus , which is also a parasitoid of polyommatine Lycaenidae and much more frequently found. The females can be separated by the length of the ovipositor: in the present species the ovipositor sheaths are about the same length as the first tergite, whereas in notatus they are only about half the length. Horstmann in his draft key commented that males could not always be separated from those of H. notatus . In the present species there is usually less darkening of the orange hind tibia, and the coloration of the median outer part is yellowish rather than red, but this is not a very reliable guide. This species has been reared from the larvae of the lycaenid butterflies Agriades pyrenaicus (Boisduval) , and Plebicula dorylas (Denis & Schifferm̧ller). Specimens reared from the latter host are in Bern , 3 specimens , including a female paratype , reared from the former host are in NMS and a further female paratype from the same host is in ZSM. We have seen specimens from Switzerland , France and Spain .