I'm writing ekphrastic poetry about a holiday I took to China. Is there a Chinese equivalent of the saying "like moths to a flame"?
Not to my knowledge, no.
I cannot think of any Chinese sayings that mean "like moths to a flame." However, there are plenty of other sayings you could pick from that might enhance your poem and give it a cultural feeling.
I don't know the context of your poem, so I picked Chinese story sayings that had to do with doing stupid things (like how moths run into flames).
塞翁失马(SaiWeng loses a horse) This saying means that good might not be good, and bad might not be bad. The story goes that SaiWeng's horse ran away (bad) but then came home with a wife (good) but then his son was riding it and broke his leg (bad) but then it meant that he did not have to fight in the war (good). Basically, there are unintended consequences so we can't know if something is good or bad.
画蛇添足(Adding legs to a snake) This saying means that one added too much which detracted from the overall value. The main character in the myth is a great drawer, and draws an intricate and beautiful snake. However, he goes too far and adds legs, making it no longer a snake, thus ruining his drawing.
此地无银三百两(There isn't 300 silvers on this ground) This saying means that one makes something obvious by saying the opposite. In the story, a person buries his treasure, and writes a sign saying "there isn't 300 silvers here" to avoid thievery. When the thieves come, they know exactly where the treasure is because of the sign.
笨鸟先飞(Stupid birds fly first) Might be interpreted to be a little offensive. It is a metaphor for people, meaning that if one isn't as talented, he or she should get a head start because he or she is slower.
Hope one of these Chinese sayings helps out your poem.