Don't know what they are but have you tried cutting them open with a hacksaw? I had some insanely hard little pumpkins last year that were impossible to get a knife through. I had to use a hacksaw on them to saw them in half so I could get to the seeds (roasted the seeds for snacking).

Rodney

Thanks for the suggestion Rodney! A hacksaw might work if you could put them in some sort of vice to hold them while cutting. Since we have neither, we haven't tried it. Right now, I just want to get rid of them. There is no way they are going into my compost! It's as if they were the result of a mad scientists experiment. Even the SVB and squash bugs stayed away from them, while happily munching on my nearby buttercup squash.
We may have to burn them.

I wonder if soaking them in water for a day or two would soften them enough to where you could easily bust them up with a hammer (or by some other means). Small chunks would be easier to get rid of than whole squash.

Rodney

before you bake them, can you try and thow them up in the air and have them land on your concrete driveway? That out to work.

The only reliable way I found to crack the little monsters was by inadvertently letting them explode in the oven. Very messy. Even then, the shards of the shell are like very hard plastic. You could easily cut yourself with them. These are not normal. They are Frankensquash. I have tried smashing them on our brick walkway and that didn't work either. I think they are headed for the burn bucket.

Sounds like my black walnut challenge some years ago.
They sound more like gourd than squash.

If they taste good, the I is worth the challenge. Here is what I would do:
Drill them ( upside, as they stand firm) === heat your oven to 300F === bake as many of them as you can , to make it pay for the electricity. You can also put some water at the bottom of the pan to soften the rind a bit., === after cooking, split, take the meat use it === if too much freez for pie making
AND FINALLY, NEVER , EVER AGAING BE TEMPTED TO PLANT THEM...hahaha

Could the seeds have been switched? I found a reference to "Cannon ball gourds" for crafters - picture attached.

Here is a link that might be useful: Cannon Ball Gourd

Oh dear what a mess you are all getting in. This is a cannon Ball Squash. Halve them using a large sharp knife and a mallet cutting in half through the stem. Scoop out the seeds with a small metal spoon. Place the halves cut face upwards in a pan of water. Level to be just below the tops. Bring to the boil and simmer for 20 - 25 mins. From this point onward its all yours to create what you want. I like a small dab of garlic butter but anything goes really. They can also be baked in the oven with suitable filling.

The last post to this thread was five and half years ago!! One would hope the issue has been satisfactorily resolved by now :-))