tapeworm
蚘 centers on a parasitic worm that lives in the intestines: a tapeworm. The meaning is specific to this intestinal parasite.
蚘 combines 虫 (insect/worm) with 尤, which likely contributes a phonetic element. The character specifically denotes a tapeworm or intestinal worm.
The left side 虫 means insect or worm, and the right side 尤 looks like a twisted shape. Picture a long, flat tapeworm twisting inside the body: 蚘 is that intestinal worm.
For カイ, imagine a tapeworm that looks like a twisted kite string: kite -> カイ, and the worm is as long as a kite tail.