The wisdom of introducing earthworms to a yard

I've started looking after my own lawn and garden since retiring a couple years ago. The location is the southern Sacramento Valley in the town of Davis, CA.
One thing that struck me is the relative scarcity of earthworms in both the garden and lawn areas. Part of the issue is apt to be former management practice: For probably the past twenty or more years the yard was cared for by a commercial "mow and blow" firm. In digging in both flowerbeds and the lawn itself earthworms are seen, but rarely; maybe one every second or third shovelfull of dirt.
At the same time, there seem to be lots of snail, slugs, sowbugs and outdoor cockroaches. This implies that there's enough moisture and food to support detritivores in some numbers.
I've switched to mowing the lawn without a grass catcher and raking at least some of the fall leaves into the flowerbeds to suppress weeds. Two years on, the earthworm population hasn't changed much. Far as I know nobody has used pesticide sprays in years, I used a little Sluggo until learning that it's bad for earthworms last year.
The present drought has persuaded me to replace all the sprinklers with drip irrigation. It's certainly more efficient than sprinklers and cheaper than relandscaping.
Drip irrigating the lawn has required about 1800 feet of Netafim Techline CV dripline. For now it's just stapled to the surface as I shift it around to match the water supply to the sun load. It's possible to mow over it, very carefully, with a reel mower.
Once the position is set, it'll be time to hide it. Trenching it in is one option, but that's a lot of work. According to Darwin's book on earthworms, they'll raise the soil level an inch in about five years under ideal conditions. I have the time, but it does not look like I have the earthworms 8-)
One approach is to simply wait and see if the population increases, but the fact it hasn't changed much in two years bodes ill for that notion. Some sort of nightcrawler seems like the best bet, but what kind and what stocking density are absolutely unclear to me. Alternatively, maybe something else is wrong and adding new species won't help at all.
Thanks for reading, any thoughts appreciated!
bob prohaska
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You're post goes on about a supposed lack of earthworms on your property but the way you've done your measurements leaves me unconvinced you have an actual problem.
You go on to suggest importing worms is a "solution". I think you are trying to solve a problem that doesn't exist.
Anything wrong with your lawn or garden that suggests you do have a problem?
I think I have lots and lots of worms, even in the lawn. If I did some digging, I'd expect to find one every second or third shovel full.
In the compost heap, maybe 1 every shovel full.
I think importing worms is a waste of time. They'll be there if the conditions are good.
--
Dan Espen

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Dan Espen wrote:

The main thing that determines if you have earthworms are the conditions, organic matter and some moisture in the soil, not whether you have imported any.
--
David

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User Bp wrote:

in an arid climate it would not be common to see much worm life at the surface.
what type of soil do you have and how large is the area?

sowbugs can do ok in fairly dry spells when worms would go deeper and be more dormant. snails and slugs may do ok on dewfall.

putting the clippings back on the top will help, but if there isn't quite enough moisture and the worms are scarce it can take a while for a new population to reestablish itself.

Darwin wasn't in an arid climate...

i'm quite sure that night crawlers will not be the right worm to put in even if there was enough moisture to support them (they grow into their burrows through time and don't fare well when moved or raised in captivity -- they also like a bit of clay in the soil).
i suspect your biggest challenge is the lack of enough moisture. the amount of money spent on irrigation setup and water over the lifetime would likely cover the cost of doing something else instead. putting in drought hardy plants that can withstand a prolonged drought makes much more sense in such an arid climate.

irrigating a lawn in an arid climate so that it needs to be mowed more often is pretty foolish IMO. any worm life you have during the wetter spells would be nice, but more likely you'd just be feeding the birds an expensive meal if you put worms on a lawn.
compost your veggie scraps and any spare organic materials using a mix of native worm species and then amend your gardens with the worm castings. mixed with the worm castings will be cocoons and tiny worms. some of those will survive and increase the populations, but i still think it would be an error to expect high worm populations in an arid climate.
songbird
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What I have often read, and my experience matches it, is that adding worms is about as helpful as taking your cash and digging it into the soil.
Unless earthworms are completely absent (not your case), the population tends to vary with the soil condition and available food. If your soil is not inviting to the new worms, they will migrate or die.
I'll repeat the Ruth Stout rallying call -- you need more mulch. If the worm food is not staying moist (as often happens with thin mulch layers), the worms won't eat much, and they won't increase.
--
Drew Lawson While they all shake hands
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http://ecosystems.serc.si.edu/earthworm-invaders/
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That's an interesting link. I'm not in an old-forest area, so environmental disruption isn't an issue.
But, as others point out, there are a few worms around. If there aren't more, it's not because something is wrong with the worms. The environment is wrong, most likely moisture. Drip irrigation will help a little, but it's impractical to raise the soil moisture significantly.
Looks like the best course is to wait and watch, and dry to devise a tool to efficiently bury dripline.
Thanks to all for your thoughts,
bob prohaska
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On Tuesday, May 26, 2015 at 11:53:45 PM UTC-4, User Bp wrote:

I first came across the worm introduction idea in this book: (Amazon.com product link shortened)
which I HIGHLY recommend. I had no idea of the amount of ecological change caused by the European "invasion."
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