The flowers are visited by a wide variety of insects (the generalised [[pollination syndrome]]).<ref>{{Cite journal | doi = 10.1111/plb.12328| pmid = 25754608| title = Competition for pollinators and intra-communal spectral dissimilarity of flowers| journal = Plant Biology | year = 2016| last1 = Van Der Kooi | first1 = C. J.| last2 = Pen | first2 = I.| last3 = Staal | first3 = M.| last4 = Stavenga | first4 = D. G.| last5 = Elzenga | first5 = J. T. M. |volume=18 |issue=1 |pages=56–62| url = https://researchpure.rug.nl/enws/publicationsfiles/caee8d0d-9724-4056-9d45-93162a5a7afc78585910/Competition_for_pollinators_and_intra_communal_spectral_dissimilarity_of_flowers.pdf}}</ref> Some species in the insect order [[Lepidoptera]] frequently use the willowherb as their primary larval host-plant, examples including the elephant hawk moth (''[[Deilephila elpenor]]''),<ref>{{Cite book|url=https://books.google.com/books?id=XZPSBQAAQBAJ&q=deilephila+elpenor&pg=PA338|title=Pests of Fruit Crops: A Colour Handbook, Second Edition|last=Alford|first=David V.|date=2016-04-19|publisher=CRC Press|isbn=9781482254211|language=en}}</ref> bedstraw hawk moth (''[[Hyles gallii]]''), and the white-lined sphinx moth (''[[Hyles lineata]]'').<ref>The Xerces Society (2016), ''Gardening for Butterflies: How You Can Attract and Protect Beautiful, Beneficial Insects'', Timber Press.</ref>
