[CT Birds] Comment on Worms
sffaulkner at comcast.net
Sun Aug 21 11:30:13 EDT 2011
Now THAT is an interesting question. Our "common" earthworms -- primarily
the common earthworm Lumbricus terrestris -- are invasive species thought to
have come to North America with early European settlers. As they spread,
they have effectively wiped out native earthworm populations -- but note
that there ARE native earthworm populations (of the 183 species of earthworm
found in North America, 60 are exotics -- meaning that 123 are natives; see
The native worms were likely the sources of food for the robins (my
assumption) along with your assumption of other foods such as grubs, before
introduction of the common earthworm. That there were no native earthworms
is an erroneous understanding by lots of people.
Biologists agree that the latest Ice Age wiped out native earthworms
populations in soils covered/sufficiently chilled by glaciers 10,000+ years
ago -- an area delineated by the Pleistocine glacial margins
(http://www.uwgb.edu/dutchs/research/what-if/whatif.htm). But note that
this is not as big an area in the U.S. as some people think -- there is a
dip of the margin into the central U.S. and New England, but it does not
include most of the country. This left a lot of room for native earthworms
to continue living. It might be that robins had a limited North American
distribution prior to the introduction of the invasive earthworms - I'd be
interested to know other thoughts on this.
The problem with the invasive earthworms -- and the reason for growing
biological concern about them -- is that the invasives are much, much more
efficient decomposers of leaf litter than our native species. What used to
be a deep leaf litter in our northern hardwood forests is now being quickly
eaten by earthworms, leaving a very shallow organic layer over the soils of
the forests. The forest duff used to be a reservoir of slowly accessible
nutrients to the vegetation, but, with rapid decomposition, it leaches away
quickly with rainfall and snowmelt, leaving the soils nutrient-poor. There
is considerable research going on right now about the long-term impacts of
these invasive worms. For one, the poor soils are blamed for the decreased
understory in our forests. We may find that these earthworms also are
responsible for things like "maple decline", increased inability of our
native trees to resist diseases and fight off other invasives (such as the
ash borer), increased vine growth, and more. Research is already pointing
to a bad combination of poor soils and increased carbon dioxide leading to a
rapid shift in plant biodiversity and populations (e.g, poison ivy is
proliferating!). The earthworms likely have a widespread negative impact on
the entire deciduous ecosystem -- a biologist in Georgia, for example, has
been finding that the invasive worms are too large to be eaten by native
salamanders (unlike the native earthworms), leading to salamander decline.
All this leads to why biodiversity is critical - plus it greatly impacts our
enjoyment of birding. I love Thomas Jefferson's quote, "For if one link in
nature's chain might be lost, another might be lost, until the whole of
things will vanish by piecemeal."
Maybe those robins should step up their eating!
Thanks for giving me a diversion from grad school research. now back to it!
----- Original Message -----
From: "Carrier Graphics" <carriergraphics at sbcglobal.net>
To: <ctbirds at lists.ctbirding.org>
Sent: Sunday, August 21, 2011 10:15 AM
Subject: [CT Birds] Just a quick question........
> Just a quick question that i was pondering recently.....
> If their were no (indigenous) earth worms, nor Japanese beetle grubs
> during the
> pre European times here in North America, What the heck did the American
> I do believe their were some indigenous grubs here, but it is stated their
> definitely no earth worms, which i believe came over on European plants.
> Our American Robins seems so adapted at finding and pulling out these two
> species. Any bird historians have the answers out there?
> Thanks - Paul Carrier
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