From inter- +‎ devour.

interdevour (third-person singular simple present interdevours, present participle interdevouring, simple past and past participle interdevoured)

1. (rare) Of many people, creatures etc.: to devour each other.
   • 1603, Michel de Montaigne, chapter 12, in John Florio, transl., The Essayes[…], book II, London: […] Val[entine] Simmes for Edward Blount[…], →OCLC:

     Epicurus said of the lawes that the worst were so necessary unto us, that without them men would enterdevour one another.

   • 1987, Richard Preston, First Light:

     His prime suspect for cannibalism was a nightmarish object — a pack of nine galaxies in a feeding frenzy, interdevouring one another.