From the Super Mario Wiki
Purple Klaptraps are found in several areas in Donkey Kong 64, first appearing in Jungle Japes. Purple Klaptraps are immune to all direct attacks that the Kongs have, even being completely immune to the Kongs' shock wave attack; using it will just hurt the Kongs, while the Purple Klaptrap is unaffected.
Fortunately, Purple Klaptraps can be defeated by blowing them up with an Orange, or by using a musical instrument. When defeated, a Purple Klaptrap will leave three Oranges behind.
Because the Purple Klaptraps are immune to all direct attacks, the teeth of Purple Klaptraps will never leap from their bodies and attack the Kongs whenever they're defeated.