insects build volcanoes in lawn, wasps attack
I have something strange going in my tall fescue lawn. Recently I have noticed bumps of dirt about 1/2" to 1" high when walking on the grass with bare feet. I have occasionally dug through the grass and broken apart these lumps of dirt, but so far have not found anything.
Over the past few months I have simultaneously noticed a massive wasp infestation of my lawn. They look similar to what we call "yellow jackets" (which are honey-bee size and shape), but they have longer back legs and are not attracted to the typical yellow jacket trap.
I am quite sure I do not have wasp nests under the eaves of the house or in the grass. I have looked and looked, but have concluded the live elsewhere and just come to my lawn to hunt.
Occasionally I have seen a gathering of several wasps in one area on the grass. Thinking I may have found their nest, I investigate. I do not find their nest, but instead find them tearing apart some sort of insect larvae. Yum!
So I conclude these volcanoes in my grass and the wasp smorgasbord are related. There must be some sort of bug pupating in these mounds of dirt.
Does this sound like a reasonable conclusion? What sorts of bugs could these be?
I do get a few small white moths flying up out of the grass when I walk on it, especially in the late evening. I have not noticed any ill effects to the grass. I fertilize it a 2 - 3 times a year and water the minimum to keep it green. I do get some brownish blades scattered throughout, but this seems to go away if I give it more water. Just trying to conserve in drought-stricken N. California.
I also have quite a few fruit trees: peaches, apples, apricots, plums, citrus, cherries, etc. However, I do not see too much insect activity on them. I do think I got a few hits on my peaches, possibly Oriental Fruit Moth, but I can't be sure.
I'm a little reluctant to just douse my entire lawn with insecticide without knowing a little bit more about what is going on. Not to mention this would not be good for the heavy earthworm population. How can I figure this out?