Ants on Radishes

I planned to make a spring salad tonight, and what could be better than adding a few crunchy, spicy radishes to top off some micro greens? Radishes, like many vegetables, are so much better fresh from the garden that they almost seem like a different vegetable from what you get in the grocery store. Plus, they grow from seed very fast and easy in early spring.. This year, I am growing Cherry Belles from Territorial Seed. 

Anyway, I've been checking on the radishes fairly frequently lately, since they grow so fast.  About a week ago, I didn't see any ants.  Today - a lot of ants.  They are small and black.  They seem to be tunneling, as well as crawling on top of the soil quite a bit.

The radishes actually seem fine so far.  I didn't see any damage on the leaves, and most of the mature radishes' red shoulders look unharmed.  But perhaps the ants only just arrived and their damage isn't yet apparent to me.

I will try to post some pictures of them later today.

***UPDATE***

Oh, how wrong I was.  This evening when I pulled some radishes, I discovered some serious ant damage.  They appear to have shaved chunks off of the radishes.

First, here is a "before" picture of radishes I picked a week ago, with no damage:

Now here are the "after" pictures of the radishes I picked today:

    

One of the radishes was even worse - a mere splinter of a radish.  When I pulled the radishes, there were so many ants, it looked like the soil was moving.  Ugh.  Here's a close-up of the ants on a rock, where you could see them:

What do I do?  Most of my radishes remain in the ground, and I don't want to lose them all. 

***UPDATE***

Tonight I found the same bug on two of my radish plants.  The ants are still all there.  This second bug was nestled in the very lowest part of the radish greens, just kind of hanging out, not moving or anything.  The ants were moving all around them.

I picked the bug off the radish and held it in my palm to take a picture.  At first I thought the bug was dead, because it didn't appear to have any legs, and it rolled around in my hand like a dead thing.  Then the weirdest thing happened.  All I had was my phone to take a picture, so I fumbled around a bit.  While I was fumbling with the camera, all of the sudden the bug came to live and started wriggling.  It was like the thing was asleep, and then it woke up. 

I took a couple of pictures as best I could and then snapped its head off.

Like I said, I found these suckers on two different radish plants.  Perhaps they are the real culprits.  Thoughts?

***UPDATE***

I talked to Amy on the phone about the problem, and she said that the ants probably aren't the ones doing the actual damage. But ants are often a sign that there's some other pests at work you just can't see. For example, ants like to "farm" aphids - but I know what aphids look like, and there are no aphids on my radishes.

Amy suggested I try diatomaceous earth as well as Bt, both natural pest deterrents. these would take care of a variety of potential pests.

I had some Bt on hand, so I sprayed that on the radishes about 3 days ago. I don't have any diatomaceous earth but plan to go pick some up soon.

Results so far: the Bt seems to have worked!! It took a few days to see a noticeable difference, but this morning when I checked the radishes, I saw that the ants are almost all gone and the damage to the radishes seems to have slowed and/or stopped.