help and advice on feeding adult swallows

Hi i am just looking for some advice on what to feed my adult swallow bird as i know they eat insects so his main diet has been meal worms and wax worms,
   
but i would like to vary this for him so just wound if i could feed him maggots and earth worms from a fishing tackle shop because i know i cant feed worms from my garden as they my have parasites? i have tried dried meal worms etc but he wont eat that.
   
i hand reared my little fried when he fell out of his nest in my horses stable, i tried to release him but he just keeps coming back so now i have adopted him.
   
kind regards Emma.