> I'm looking for information on earthworms, for a Biology project
> which needs sources. What I need is to know about their habits, likes and
> dislikes. I want to compare numbers - wet mass - with where they live, in
> woodlands or grassland. Does anybody have any advice?
> Yours, Diana, new member to the list.
>> <88PROBSTD at clsg.org.uk>
A bit I did a summer ago:
EARTHWORMS MORE OR LESS
by Millard C. Davis
Charles Darwin once presented figures on the large, even astounding
numbers of earthworms in field soil. Realizing that these worms are
beneficial to agricultural and horticultural grounds as well, I did a study
during the summer of 1996 to estimate their numbers in vegetable and
flower gardens and lawns. It is interesting to consider that these may be
part of the original earthworm fauna of this part of North America, since no
lumbricids survived in soil of the Pleistocene glaciation (2: 225), the
terminal moraine of which snakes across northern New Jersey from near
Lake Perth Amboy through the Lake Hopatcong area to the Delaware River
at Belvidere (13: 122). How rapidly earthworms might have spread with the
retreat of the glacial lobes is indicated by the following (4: 20):
There is little information on the horizontal dispersal of earthworms,
though Hamblyn & Dingwall (1945) claimed A. caliginosa could advance
by 10 m per year from inoculation points in recently limed grasslands.
Stein et al (1992) studied the horizontal dispersal of A. caliginosa, A.
longa and L. rubellus in permanent grassland between 1983 and 1990 and
found an overall rate of 13 m per year. L. terrestris has been found to
move up to 19 m on the soil surface in one night (Mather & Christensen,
The overall site was an old farm, Barclay Historic Farmstead, Cherry
Hill, New Jersey, of thirty-two acres of woods, marsh, stream, open
grounds, and farmhouse, dating back to about 1822; it had been preserved
by the Township of Cherry Hill as a living museum. Thus tours of history,
done primarily by a society known as The Friends of Barclay Farmstead,
are held, often in clothes typical of the early nineteenth century, in the
house and on the closely surrounding grounds. About four acres are left
in a gardenable condition for the public to rent and garden plot by plot, thus
preserving the original usage as a working farm. Two sites are used, 8
meters apart; one, roughly in the shape of a chair is 10,593 m2 and the
other a rectangle of about 27 x 96 meters or 2592 m2 in size, a total of
13,185 m2 or 3.35 acres. Over 100 plots, averaging 8 by 10 meters, or
about 80 m2 each, were worked by gardeners this summer, an average
rental. Another couple and I took care of a plot that was about 8 x 13m, or
104m2. Plots were mostly planted to vegetables, though flowers were
generally included; the township has suggested that twenty percent of each
plot have garden flowers so as to keep the floral aspect strong. In
addition to the Barclay plots I investigated a few local flower gardens, all of
which were much smaller than the 80 m 2 format. For each overall
area I also checked for earthworms in neighboring lawn grass. The
earthworm digs were done with a spade, quickly lest injured worms send
out alarms that would cause others of the kind to disperse (1: 155), and
each dig was a cube that measured approximately 10 cm.3 In terms of
surface, that would be 103.2 cm.2/dig, 96.9 digs per square meter. In the
Barclay plots I made 5 digs each, spaced out in an X form, with a dig
toward each corner and a fifth in the center. Home garden plots varied
according to the shape of the plot, mostly slender and longitudinal.
Through July and August I investigated 19 Barclay garden plots and 5
home ones, giving me a total of 135 digs. Paralleling these were 19 lawn
digs, 6 of these being in home lawns. The 135 garden digs resulted in a
total of 40 earthworms, or 0.30 worms per dig, making an estimated 30
worms per square meter; in ten of these digs I unearthed plants to see if
any worms were there and found none. The 19 lawn digs resulted in 52
earthworms, or 2.74 worms per dig, estimating out to 274 worms/m2. This
gives a ratio lawn/garden of 9.13 :1 worms. Thus lawns would seem to
average far more earthworms per volume than gardens. Early in November
I also made seven digs in a lawn in Leavenworth, Kansas, and got an
average of 6.4 worms per dig as confirmation of the New Jersey finds.
Only two of the gardens had had any pesticide applied, and there were no
observed differences here, but the samples were too small to admit to any
conclusions. Several of the gardens of the above listing had been
mulched, either in part or in whole. Of the mulched digs, 22 (out of the
above 135), I counted 25 earthworms or an average of 1.14 per dig, or
114/m2. In the non-mulched 113 digs I found 15 worms, or an average of
0.13 per dig, or 13/m2. When we compare the mulched dig average,
1.14, to that of the lawn digs, 2.74, we get 0.42; thus there are about 40%
as many earthworms in a mulched garden as in a lawn. Comparing the
average in non-mulched gardens, 0.13, to lawns, 2.74, we get 0.47, or
slightly less than 5% as many. Some of the garden plots where I dug
were grassy, especially along a lawn side. Of 10 of these digs, part of the
original 125, I found 4 worms, or an average of 0.4 worms per dig.
I think that the explanation for this pronounced difference in lawn
versus garden is that the earthworms here find more preferred plant matter
both on and in the soil of lawns. Grasslands have been found to support as
many as 30-2,000 earthworms in one square meter of soil (10). Thus it
should be no surprise that earthworms may be so active in their consuming
that species in tallgrass prairies can be so active that they may consume 4-
10% of the total A horizon of soil, amounting to 10% of the total soil organic
matter in the top 15cm or 100-300% of the annual root biomass production
Mulch does add edible plant matter to both the soil surface and the
subsoil. Lawns offer blades of grass which the worms cut and add to their
middens for later ingesting, after bacteria and fungi have been breaking the
plant tissues down. The garden plant leaves are, on the whole, far out of
reach on long comparatively thick stems, while the grassblades, slender
and sufficiently succulent, begin essentially at ground level. Fallen leaves
in general are often quick to disappear to earthworms, the soft leaves of
such trees as ash, basswood, and maple quickly decaying and then being
devoured by the worms, becoming humus topsoil within a matter of a few
months (12: 105). Also those worms appearing above ground in the
gardens are more open to damage from drying and ultraviolet light, as well
as being detected by potential faunal enemies.
Finally, gardens are often turned over, and the Barclay plots are
ploughed up, each spring and fall. A cover of winter rye grass is, however,
added to the Barclay garden grounds each October as winter cover; this
would probably enhance earthworm presence there where it exists already
and would invite more in from the surrounding lawn. In fact, during early
October I made 20 digs in Barclay plots, each dig about one meter in from
the lawn. Nine of these resulted in one worm each, one had two, an overall
average of one per dig or 0.50 worms/dig. Probably of greatest
significance is this evidence of worms working their way into the garden, in
these cases non-mulched garden plots.
As a check lest these worms were simply ones that had been there
before in the parts of the gardens next to lawn grass, I reviewed my charts
of the digs and culled out those which were made alongside lawn grass. In
the total of 32 such digs I found 10 worms, or 0.31 worms/dig. Of the 32
digs, 27 were in non-mulched plots, and here I found one worm, or 0.04
worms/dig. In the five in mulched soil I found a total of 9 worms, or 1.8
worms/dig. These results seem to indicate that the worms found in the
plots during October where grass was coming in were indeed invaders.
Their return to the garden space follows findings in no-tillage agriculture,
where plots with weed returns to soil reveal that the 35% of weed biomass
N (38 kg N.ha-1) is mineralized rapidly; weeds act as reservoirs of nitrogen
(N), with the improved structure of the soil benefiting land undergoing
drought conditions, fungi taking a major role in the cycling of nutrients (8).
This activity of fungi is known to take place even among fallen pine
needles once they have been ingested and excreted by earthworms, with
the feces of the lumbricid Dendrobaena octaedra usually being penetrated
by the brown hyphae of the mycorrhizal fungus Cenococcum geophilum
Evidence here presented seems to suggest that one might do well to
make a point of introducing earthworms into ones garden, possibly from
the nearest lawn, their benefits being at least that they aerate, drain, and
churn the soil, mixing it further in as during their burrowing the worms send
organic matter deeper and lower soil is brought up as castings (2: 224).
Their burrowing also reduces soil compaction (4: 19).
Since earthworms do best in soils with much organic matter,
especially those with humus on the surface (2: 223), mulching can be
valuable, as seems indicated by this present study and was shown earlier
in areas of a tropical forest ecosystem where mulches of Acioa, Gliricidia,
and Leucanea were shown to increase earthworm populations by 40%
(11). Some gardeners use wheat straw as a mulch; possibly its
decomposition by earthworms can be enhanced by inoculating it with
saprotrophic fungi, with certain species of fungi being preferred over
others by earthworms and also being more likely to be dispersed though
the soil by worm travel (7: 1212). This latter transfer of soil
microorganisms by earthworms has also been found occurring among
genetically modified microorganisms (GMMs), being moved both vertically
and horizontally (4:2), with lumbricids in general being probably the most
significant transporters of fungi in soil (4: 20).
Earthworms are especially important movers in many temperate and
tropical grasslands and forests, where they often dominate (4: 23); fertile
agricultural soils that are dominated by bacteria also find earthworms
predominant (4: 24). Again, the importance of mulching appears, for the
presence of surface soil organic matter seems to increase the burrowing
activity of worms and thence raise their potential for transporting useful
Liming can also help, for acid soils can be unfavorable habitats
because they lack the free calcium ions needed to eliminate excessive
carbon dioxide in the blood(2: 224), the carbon dioxide being combined
with the calcium and excreted as calcite (2: 213), calcium carbonate (3:
298). If these efforts were made, one might even see more robins
pecking in ones garden, a thing conspicuously missing in the Barclay
1. Agosta, William. 1996. Bombardier Beetles and Fever Trees. Addison-
Wesley Publishing Company, New York
2. Barnes, Robert D. 1963. Invertebrate Zoology. W. B. Saunders
3. Borradaile, L. A., and F. A. Potts. 1959. The Invertebrata, 3rd Ed.
Cambridge at the University Press.
4. Dighton, John, Helen E. Jones, Clare H. Robinson and John Beckett.
1995. The role of abiotic factors, cultivation practices and soil fauna in
the dispersal of genetically modified microorganisms in soils. This
paper is a summary of the findings reported to the Department of the
Environment (U.K.) under contract PECD 7/8/234 to review the
potential of soil fauna and abiotic factors to disperse genetically modified
microorganisms (DoE, 1995).
5. Hughes, M.S., C.M. Bull, and B.M. Doube. 1996. Microcosm
investigations into the influence of sheep manure on the behavior of the
geophagus earthworms Aporrectodea trapezoides and Microscolex
dubius. Biol. Fertil. Soils,22: 71-75. In 10: 21.
6. James, S. W. 1991. Soil, nitrogen, phosphorus and organic matter
processing by earthworms in tallgrass prairie. Ecology. 72: 2101-2109.
7. Moody, S.A., M.J.I. Briones, T.G. Piearce and J. Dighton. 1995.
Selective consumption of decomposing wheat straw by earthworms. Soil
Biol. Biochem. Vol. 27 No. 9, pp. 1209-1213.
8. Parmelee, R.W., Beare, M.H., and Blair, J.M. 1989. Decomposition
and nitrogen dynamics of surface weed residues in no-tillage
agroecosystems under drought conditions: influence of resource quality
on the decomposer community. Soil Biol. Biochem. 21: 97-103.
9. Ponge, J.F. 1991. Succession of fungi and fauna during
decomposition of needles in a small area of Scots pine litter. Plant and
Soil 138: 99-113.
10. Stockli, A. 1945. Schweiz Landwirts Monatshefte, 24 ( ): 3-19. In
MacFadyen, A., 1957, Animal Ecology, Aims and Methods, Pitman and
11. Tian, G., Brussard, L., and Kang, B. T. 1993. Biological effects of
plant residues with contrasting chemical compositions under humid tropical
conditions: effects on soil fauna. Soil Biol. Biochem. 25: 731-737.
12. Thomson, Betty Flanders. 1958. The Changing Face of New
England. The Macmillan Company, New York
13. Widmer, Kemble. 1964. The Geology and Geography of New Jersey.
D. Van Nostrand Company, Inc., Princeton, New Jersey
Millard C. Davis <mildavis at earthlink.net>
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