have little perfectly round concave holes in dirt under a porch roof with no grass around it.

Question

don't know what is making the holes so we don't know how to treat to get rid of whatever is doing this.  not sure if it is bees, ants, spiders, etc.  the holes are about the size of a pea or smaller and are perfectly round and concave.

Answer 1

It seems that you have a spider problem.  The best way to kill them is with vegetable oil.  The spider breathes through its skin, the oild will stick to the skin and not allow the to breath, they will die.  And you dont need much, just a cup for an area of 24" x 24", best to treat it now, rather than allow it to get worse. -Birdy

Answer 2

No, sounds like ant lions, not spiders. BUT, are they holes that go right down into the ground or cute little conical depressions?  Is the soil there sandy or organic? Do you see webbing?  It could be a kind of bee or wasp. Do you see anything coming and going?  It's inappropriate to spread pesticides, even horticultural oils, until you know what you have. Why kill a beneficial insect?  (Ant lions are beneficial insects just like many kinds of wasps and bees.)

Answer 3

It sure sounds like nightcrawlers......they only way to know for sure it to pour a lot of water there and watch what comes up.............they are much longer and faster than regular earth worms.  They are the best to use on the end of a fishing line.

Answer 4

Sounds like some big earth worms.  Put a trail cam on it to see what comes out.  Some people call them night crawlers.  You could flood that spot and see what comes out..............