Ben Levin says don't worry.
FWIW, I'd worry a little bit. There are lots of reasons a VFT will turn black
after trying to digest a meal, lack of humidity/water being a prime factor in
my experience. My VFTs snack constantly and consistently on Daddy Longlegs,
and since the body tends to be small, only the legs stick out, and the plant
can close about the narrow-diameter obstructions and digest regardless. Mine
NEVER turn black from daddy long legs (though they may be bigger in Tennessee
than in Virginia), which might lead me to worry (a little bit) about other,
more horticultural causes.
Just my $.02 (US)
Jay Lechtman
L235@aol.com