Question
Thanks Ken.  1) Does my description of the little mounds of dirt sound at all like moles?  2) would grub damage to the grass show up as dying grass blades or not necessarily.
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The text above is a follow-up to ...

-----Question-----
Hi Ken:

I hate to again be writing you with a long question, but I've got two complicated things going on in one area in my yard.  The two things may be related. The area in question is primarily under a large ash tree--quite shady.

1)When I rake (even "blow" leaves) the grass seems easily uprooted.  The grass itself appears healthy except that I believe I could rake it out easily.  This area is shady all summer.  We have had a lot of rain (12901 zip). Would something eat roots without killing the grass?  Or are roots just weaker in these shady areas.  I do think this area has been this way in the past when I raked leaves, but this year it seems more extreme? Indeed, during the summer this shady area often seems to have the best grass, but then seems thinned in the fall--I always thought it might be from leaves laying on the grass until I raked.  But now I wonder if it is something else, because of.......item 2:


2) What would make very small mounds of dirt, about 2 inches diameter and up to an inch tall--like little volcanos?  I suspected moles (and thus grubs as the problem for question "1" above).  There is no sign of mole trails--just these mounds.  No sign of a mole entrance--at least nothing that looks like any pictures I've found of moles/voles.  Do earthworms do anything else make mounds like this?

I can see the mounds clearly in a couple of spots that have just dirt.  The mounds look as though the dirt was pushed upward but there is no opening in the top of the mound.  The dirt just appears soft and loose.

The mounds are not so visible in the grassy area, but I believe they are widespread.  The area is bumpy to mow.  I think the mounds might actually be the areas that "tear" easily when I am raking.

I assume this fragile grass and the mounds might be inter-related:  grubs causing the weakned roots, moles eating the grubs.  But the grass is not dead, I did use season-long GrubEx, cooperative extension says moles don't really go after grubs, and nothing looks like the mole holes or trails I've seen.  There is no dead grass.
-----Answer-----
Grass can be challenging to grow in shade. Even shade tolerant cultivars grow better in full sun than full shade. Shallow rooted grass is common in hard compact soils, which typically happens near base of trees (root action).

Moles often eat earthworms, etc and moles are not their only diet. Mole activity can be more visible in highly watered lawns (which may also explain why grass uproots easily).

You can check for grubs by digging into the soil with a spade and looking through the root zone. If you find more than 5-6 c-shaped white maggots, you should control it.

However, your problem is probably excessive shade to begin with.

-- Kenneth

Answer
It could sound a bit like earth worm activity. They will push their casting up but there will be no opening.

Grubs tend to eat the roots of the grass. This will leave irregular patches of grass which can be "lifted up like a carpet" because the roots have been severed. The grass will die. This is different from shallow rooted grass which is easily pulled up with a rake or by traffic. Grub damage would kill the grass plants.