If you get dry ,and i do as well, what i do is soften them up a bit in a bag and just pop in some hot water.
Now some may say its cheating but i do use a caller (out of breeding season) to help get them intrested in the area i want to try and photograph .
If i dont use a caller its pot luck,but a caller gives you a better chance ,also when the bird hears the call he will ,nine times out of ten land in the same spot all the time ,he will then obviously scoot around but as said will come back to same spot,thats when the mealworm and postioning of camera and myself to get the shot is the next step...
At the end of the day its down to how much you want a good shot (close) of a Wren,some can be perfectly happy with a few grab shots but persevere with the mealworms and a caller and you will literally have the Wren eating out of your hand