Cannibalistic Polyphemus Caterpillars?

[DTDerekson]

Would anyone happen to know if Polyphemus caterpillars are cannibalistic? I had
some eggs and three emerged on one day, so I put them on some maple leaves in a
case indoors. The next day two more little larvae hatched and I put them on the
leaves with the other three.

The next day, the original three were there but not the first two! No signs of
drowning, wandering, anything. Just gone....

Hmm....

DT zone 6, USA