If you do so during the nesting season it would be better to soak them first. Young birds need things like nice succulent caterpillars and if the parent birds just stuff them full of dried mealworms they could dehydrate and die. Best not to have any fat out for the same reason.
We found out after losing a nestful of blue tits and found out it was almost certainly a mixture of those two being easily available that probably did it.