Onthophagus pennsylvanicus Harold 1871

are eaten by

• Global Biotic Interactions: Petrochelidon pyrrhonota (Vieillot 1817) (American Cliff Swallow)
• Global Biotic Interactions: Contopus virens (Linnaeus 1766) (Eastern Wood Pewee)
• Global Biotic Interactions: Tachycineta bicolor (Vieillot 1808) (Tree Swallow)
• Global Biotic Interactions: Riparia riparia (Linnaeus 1758) (Bank Swallow)
• Global Biotic Interactions: Tyrannus forficatus (Gmelin & JF 1789) (Scissor-tailed Flycatcher)

are mutualistic with

• Global Biotic Interactions: Spiranthes lacera (Raf.) Raf. (Slender ladies'-tresses)
• Global Biotic Interactions: Datura stramonium L. (Thorn-apple)
• Global Biotic Interactions: Bidens frondosa L. (devil's beggartick)
• Global Biotic Interactions: Frasera fastigiata (Pursh) A. A. Heller (clustered green gentian)
• Global Biotic Interactions: Galium trifidum L. (three-petal bedstraw)

are parasitized by

• Global Biotic Interactions: Physocephalus sexalatus (Molin 1860)
• Global Biotic Interactions: Ascarops strongylina
• Global Biotic Interactions: Gongylonema pulchrum Molin 1857
• Global Biotic Interactions: Spirocerca lupi (Rudolphi 1809)

have endoparasite

• Global Biotic Interactions: Physocephalus sexalatus (Molin 1860)
• Global Biotic Interactions: Ascarops strongylina
• Global Biotic Interactions: Gongylonema pulchrum Molin 1857
• Global Biotic Interactions: Spirocerca lupi (Rudolphi 1809)

visit flowers of

• Global Biotic Interactions: Zizia aurea (L.) W. D. J. Koch (golden zizia)