I went to a presentation last night about problem insect control. There were some really good tidbits. And there was a lot that I thought was crap. And, as always, I have questions.
So I presented a dilemma. In two different gardens I have had in the past, I had an awesome earthworm population which suddenly dropped and i would find earthworm carcasses that looked like they earthworm had wronged his woman and she cut him up with a razor. And she kept cutting on him even after he was dead.
On several occassions I found the culprit: a rove beetle. I should have taken pictures. The problem always seems to pop up right when I am trying to get a lot stuff done, so I end up not doing anything about it.
I asked the presenter how I might be able to intervene and stand up for my buddy the earthworm. Her response was unsettling: ah yes, rove beetles are excellent general predators and earthworms are their favorite. She has seen instances of a mounds of writhing roves beetles where the center of the mound was an earthworm. She felt that the rove beetle should be supported and we probably have too many earthworms anyway.
So my first thought is to introduce diatomaceous earth and set the balance to favoring the earthworms more. Or at least make a safe zone for earthworms. But I've always been concerned about the idea of DE harming earthworms.
So, my dilemma is worse. I'm hoping that others have similar experiences and maybe more observations in this space.
I have always found when favoring earthworms or anything over beetles I use ducks! Ducks are amazing at beetle control and are not 'hard' on earthworms - only getting those that hangout on top of the soil.
I doubt if there is a method of controlling them. They showed up on Earth 200 million years before mammals arrived, and will eat anything other than living plant tissue. A flame thrower might reduce this year's crop, but unlikely to affect numbers next year (unless you catch them in orgy season). An estimated 40-50,000 species have been identified, and we are probably not yet at the half way point. Good luck. All the more reason to overfeed your worms so they breed profusely!
I would think quite a few birds would eat them, whether domestic or wild. amphibians and reptiles, too. basically, all the things that would also eat earthworms. there are proven strategies for encouraging populations of all those potential predators.
I've sort of leaned toward encouraging rove beetles in the past on the assumption that more diversity is generally better. and I still lean that way. my guess is that over time, the populations would balance out as rove beetle predators get the picture and move in, particularly if somebody encourages them with inviting habitat.
some friends mentioned that they had a terrible slug problem for a few years, but plenty of earthworms. then snakes moved in and ate the slugs and earthworms. then herons moved in and ate the snakes so the slugs and earthworms rebounded, but not to their previous high levels since a few snakes evaded the herons.
diatomaceous earth would probably knock out the beetles, but it would also knock out a great many other critters that you probably want around, possibly including the worms.
and what the presenter said might be true, as well: a huge number of worms isn't all good. some decomposing vegetation that remains on the dirt for a while has several benefits. too many worms will remove that cover too quickly. I believe that's the main complaint about earthworms expanding their territory: destroying the duff layer in forests quickly decreases biodiversity, at least in the short term. a reasonable population will still incorporate vegetation in a garden into the dirt effectively, just not quite so quickly. so maybe the early worm boom is enough to accomplish an initial dirt improvement before the rove beetles show up, then the lower population will continue to improve things along with the greater diversity of critters that show up.
and keep in mind that rove beetles eat up young slugs and plenty of other unpleasant garden critters, too. they aren't just eating worms. they're also shitting all that out and cycling nutrients.
run some chooks or ducks through periodically. encourage some snakes and frogs and birds to hang around. earthworm populations might reliably take a dive once rove beetles show up, but they won't disappear entirely.