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Question about earthworms.

Millard C. Davis mildavis at earthlink.net
Thu Feb 4 21:11:17 EST 1999


88PROBSTD wrote:

> 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, 
1988).  


	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 
(6).   

	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 
(9: 108).  

	Evidence here presented seems to suggest that one might do well to 
make a point of introducing earthworms into one’s 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 
microorganisms (5).  

	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 one’s garden, a thing conspicuously missing in the Barclay 
plots.	  


References

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 
Company, 	Philadelphia  

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 
Sons, London  

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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