insects build volcanoes in lawn, wasps attack

lifespeed(9B San Jose)August 24, 2009

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?

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Sounds similar to what I had a few years ago.
Take a look on the web for cicada wasps.
At night I just shot wasp killer into the holes.

    Bookmark   August 24, 2009 at 7:41AM
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lifespeed(9B San Jose)

Thanks for the response. I am not so sure they are Cicada Killer wasps. I looked at pictures of the Western variety.

My wasps are smaller (about 1" long), and have more yellow than black. Also, a 'season' is mentioned that is from mid July to early August. These wasps have been around for 3 - 4 months.

Lastly, there are photos of burrows showing a U-shaped trench with piles of dirt around it. I have many, many small mounds under the grass typically around 1" diameter. These don't seem typical of what I have read on the web about their egg burrows. Supposedly Cicada Killers like dry, sparsely vegetated areas to nest. These small mounds are deep under the grass. I have not seen any wasps carrying prey back to their nests, either.

Are Cicada Killers the only explanation? What about another wasp variety eating grubs of some sort in the lawn?

    Bookmark   August 24, 2009 at 12:18PM
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beehive21(5b N. Central Ohio)

Scoliid Wasp/Scarab Hunter Wasp? Just from some searching, no personal experience with them...

Here is a link that might be useful: Scoliid Wasp

    Bookmark   August 24, 2009 at 12:42PM
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