Question
i have read that it is common for a trap to turn black and fall off after a feeding,
but why is this?

Answer
Hello Dan,

Contrary to popular belief, Venus Flytrap traps do not ordinarily turn black after they capture prey. A healthy Venus Flytrap will be one that receives full sunlight or an equivalent in artificial light combined with window light. A healthy Venus Flytrap typically will be able to capture and digest 3-4 insects per trap.

Occasionally, an overlarge prey item, inedible object, like fatty red meat, or low energy from inadequate lighting can cause the death of a trap.

Christopher