[CT Birds] Comment on Worms

Sarah Faulkner 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 
Blakemore, http://www.annelida.net/earthworm/American%20Earthworms.pdf). 
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!



Sarah Faulkner

Collinsville, CT

----- 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 
> Robin
> eat?
> I do believe their were some indigenous grubs here, but it is stated their 
> were
> 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 
> alien
> species. Any bird historians have the answers out there?
>
> Thanks - Paul Carrier
> _______________________________________________
> This list is provided by the Connecticut Ornithological Association (COA) 
> for the discussion of birds and birding in Connecticut.
> For subscription information visit 
> http://lists.ctbirding.org/mailman/listinfo/ctbirds_lists.ctbirding.org 





More information about the CTBirds mailing list