the common intestinal worms, the tape-worm
蛕 centers on parasitic intestinal worms, specifically tapeworms. It refers to common internal worm infestations.
蛕 combines the insect radical 虫 with 有, which likely provides the sound. The character is used for parasitic worms, fitting the insect/creature radical.
The insect radical 虫 hints at a small creature, and 有 (possess) suggests something you might have inside you. Picture possessing an unwanted intestinal worm.
For カイ, imagine a tapeworm shaped like a kite (カイト) inside the intestine: kite -> カイ, and the worm is the unwanted passenger.