https://en.wikipedia.org/wiki/Agkistrodon_contortrix#Feeding

You have to not only get rid of mice,
but voles, frogs, insects, and so forth.

Sample quote

Feeding
Roughly 90% of its diet consists of small rodents, such as mice and voles. It has also shown fondness for large insects and frogs, and though highly terrestrial, has been known to climb trees to gorge on emerging cicadas.

Copperhead populations may be reduced by non-venomous Eastern King Snakes
Lampropeltis getula
that feed on venomous copperheads.

https://en.wikipedia.org/wiki/Lampropeltis_getula

End quote