Themisto libellula is a marine amphipod of the family Hyperiidae. The species lives for 2 to 3 years, and grows up to 60 millimetres (2.4 in) over its lifetime.[2][3] They are found in large quantities in Arctic water.[4]
In the summer, they eat more lipids to store as fuel for the winter.[3] During the mid-winter, they eat copepods, such as Calanus finmarchicus.[5]T. libellula is eaten by cod, polar cod, and mammals at the ice edge.[4] In the early 2000s, the population of the species began to decrease; these effects rippled through the food chain.[4] The levels later rose in cool years, and T. libellula have moved south of the Arctic Circle.[3] They have been observed in mass mortalities, where millions of T. libellula wash up dead on the coast.[6][7]
^Koszteyn, J.; Timofeev, S.; Węsławski, J. M.; Malinga, B. (1995). "Size structure of Themisto abyssorum Boeck and Themisto libellula (Mandt) populations in European Arctic seas". Polar Biology. 15 (2): 85–92. doi:10.1007/BF00241046.