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I live in Adelaide, Australia and during this winter season during rainy weather I have been finding large numbers of earthworms dead and stuck on the concrete of our back veranda (porch.)

This isn't just a few worms, but dozens to hundreds of them at a time. It hasn't rained much this year, but when it has, the next morning there's a new bunch all dead and stuck to the cement. I figure they're breeding in huge numbers for this result.

The area just beyond the concrete is a fairly large lawn with garden beds at the back and sides. The lawn is mowed regularly, but it's been a long time (at least 15 years) since it was last aerated.

I was wondering if it was something to do with the drainage, does anyone have any (other) ideas?

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It might be more to do with the fact you're not getting as much rain as usual - earthworms surface during wet weather, and many reasons for this have been proposed, but no one really knows why they do it. There are theories about oxygen shortage in waterlogged soil, or needing to come to the surface for breeding purposes, and these are all possibilities, but the other thing they do is mass migration, usually in rainy weather, and usually in spring. If your air temperatures have been a degree or three higher than you'd expect for this time of year, they may be attemping to migrate, but didn't have time to get where they were going before the rain stopped and they got stuck on a dry surface like your concrete. The reasons for migration are also unclear, but likely to do with a large population needing more space, or the conditions they're living in are no longer hospitable. Water table changes can cause inhospitable conditions, so if anyone's had extra drainage put in anywhere and the soil is drier, that might have affected the worm population locally.

You might be interested in reading this:

http://www.accuweather.com/en/weather-news/why-do-earthworms-surface-afte/28916

As for your lack of proper lawn maintenance, if there are earthworms in the soil under the lawn (in warmer temperatures, you should notice little piles of worm 'droppings' or casts, usually in autumn or spring) they do quite a lot of aerating for you, so its unlikely to be that causing an issue. If you have never seen any piles where they've come out of the soil, then perhaps your lawn does need some care and attention...

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  • Thanks, that's really helpful. It's actually been the coldest July for 18 years according to the bureau, but cold is relative. Here in Adelaide winter is quite warm compared to some places. I haven't seen a lot of castings, but I'll keep an eye out this coming spring. Cheers. – John Judd Aug 4 '15 at 1:10

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