Maureen
I wouldn't think it will harm them, if they were freeranging out of your sight I'm sure they'd be tucking in like mad.
Mine eat every slug/wire worm/cut worms etc I can find. I have a pot with me when weeding and digging and in goes every nasty for me to take over to the hens in the afternoon. A great favourite for a treat. I also love the fact that I have garden pests, I give them to the hens to eat, result = less of a problem and pests converted into food!
And being squeamish, it absolves me from cutting, salting, drowning the wretched things, I just don't look when they have a tug of war with the big ones - oh and make sure they don't wipe their beaks on my flip flops....
Sue