"John Savage" wrote in message
om...
(simy1) writes:
Also of note is the fact that earthworms propagate very slowly, no
more than 20-30 feet per year if they have to do it themselves. There
are large tracts of not previously farmed land where they have not
appeared yet.

Wouldn't the earthworm eggs get widely distributed by rainwater runoff
and soil carried on vehicles and the roots of transported seedlings and
on the muddy hooves of native, feral, and introduced animals?
--
John Savage (news reply email invalid; keep news replies in
newsgroup)


Probably not as much as you might imagine.

First of all, earthworms deposit their "cocoons" beneath or right at the
litter layer, not on top of the litter layer or in places without litter.
In doing so, the movement of eggs by rainwater is inhibited. In fact, worms
are rarely found in erosional habitats because the organic matter that they
consume is in limited supply; the highest densities of worms always occur in
deep, moist litter.

Second, the likelihood of worm eggs being transported on tires is pretty
low. If you can successfully drive your vehicle where there are a lot of
earthworms, then I need you to come work for me - and your lawn doesn't
count! The fact is, worms don't persist very well in compacted soil (road
substrata) or in areas that are real dry (think of the gravel and other
material at the side of most roads). ... Even more important than the
preceding points is the fact that the eggs, which are deposited in a cocoon,
are more likely to get squished than transported any meaningful distance.

Third, animals, even the largest ones, have pretty well defined home ranges
or territories. I'm not talking about the entire biogeographic range of a
species, but the area occupied and/or utilized by a single animal in its
lifetime. With a few notable exceptions like migrating birds, animals only
ever use a few square miles at the most. In fact, many animals never use
much more than a few square feet. (There are a *lot* more small animals out
there than big animals.) Deer, which I presume you were referring to with
the words "muddy hooves" often occupy the same area are their whole lives,
making a circuit every 1-5 days depending on the age, gender, a reproductive
status of the animal. Other large ungulates may have larger territories,
but they are still not too likely to transport worm cocoons very far. Oils
in the fur and on the skin of the animal help to prevent mud from sticking,
and water that the animal walks through has a rinsing effect. .... In case
you're wondering, worm eggs that manage to hatch in water won't survive very
long unless the worm is one of the handful of aquatic species that exist.

Invasion fronts may move very fast (think of zebra mussels) or very slowly
(as in the case of earthworms). It may be that earthworms will never
successfully invade all of North America, but even their slow movement into
areas that were previously earthworm-free holds serious implications for the
native flora and fauna of invaded habitats. For more information on why
invasive species are harmful, email me. I have a lot of resources I can
share with you (I'm a conservation biologist).

One final thought: Part of the original post read "if they have to do it
themselves".... It might be worth noting that getting stuck to a car's tire
is not natural.