It seems that in nearly every inter-species relationship it is one of the species that does most of the killing, if at all.
Is there any pair of multicelled species that kill each other on a regular basis and whose death rates are reasonably equal, at least around 20%/80% (ignoring the few times that a prey kills a predator with a stomp, for instance)?
I’m not sure if this is true or not, but I recall hearing that in Africa, hippos and crocodiles fight each other on a daily basis and that the outcome is about 50-50.
It’s my understanding that squid don’t stand much of a chance, although they do leave nasty scars. I saw a show about giant squid recently where they showed 10-15 squid beaks from the stomach of a single whale. ISTR that this was a typical number, so a 20%/80% ratio is unlikely.