They can and do get worms from eating earthworms and other bugs, but the only way to know if you *should* de-worm is to get routine fecals done by a vet or a lab. I have many duck so I don't de-worm my flock, but if one stArts looking a little iffy, one of the first things I do is de-worm them.
Dawg53 has some good posts on how climate can affect your flock's worm burden... I'll see if I can find one for you to read.
How would you define looking "iffy"? Thanks.