
14 
late summer or in winter (Gerard 1967). Lumbricus ter- 
restris appears to move faster in the evening during the 
summer months than in the winter (Bennett 1968), Not 
only do earthworms spend more time near the surface in 
the spring and fall, some species may spend several hours 
on the surface in the evenings; they also are more active 
during these times. This closer contact with the surface, 
the portion of the soil containing the greatest amount of 
insecticide residues, and their greater activity at this time 
may partially account for the larger residues in worms in 
the spring and fall. 
Concentrations of some chemicals in the soil changed 
with time; p,p'-DDE and heptachlor epoxide increased 
whereas heptachlor decreased. Although dieldrin, 
p,p'-DDT, y-chlordane, and total heptachlors and chlor- 
danes fluctuated with time, there was no significant dif- 
ference between quantities at the beginning and after 2 
years. Without obvious decreases, neither chemical half- 
lives (Edwards 1966; Nash and Woolson 1967) nor 95 % 
disappearance (Edwards 1966) could be estimated. 
Heptachlor had disappeared from earthworms by 16 
months. Residues of the other metabolites and their totals 
in earthworms generally were greatest from 2 to 4 months 
after application. After the maximum values were 
reached, residues declined, with a general increase in late 
spring and a decrease in the winter. These highs and lows 
coincided with reported general patterns of seasonal 
behavior of earthworms. 
The 2.24-kg and 8.97-kg ai/ha rates depressed decom- 
position of soil organic matter, probably by affecting the 
organisms responsible for decomposition. Moisture reten- 
tion of earthworms was enhanced by dieldrin and hepta- 
chlor and also increased with the concentration of insecti- 
cide in the soil. Observations on the scarcity of earth- 
worms at the higher rates of application in the dieldrin 
and heptachlor plots suggest that insecticides may cause 
earthworm mortality. Maximum residues in earthworms 
did not occur immediately after chemical application, as 
one might expect, but about 2 months later for DDT and 
metabolites and 4 months later for dieldrin, heptachlor, 
and chlordane compounds. Thus, major effects of organo- 
chlorine insecticide applications on earthworm-eating 
vertebrates might not appear for several months after 
application. 
Residue quantities in earthworms declined rapidly after 
the maximums, but secondary peaks generally occurred in 
late spring, when young birds would likely be fed earth- 
worms, Thus, a potential hazard of a single application to 
earthworm-eating wildlife was still present 2 years after 
application. By not recognizing the seasonal variability of 
residues in earthworms, possible erroneous conclusions 
could be made that no acute poisoning hazard existed for 
earthworm-eating wildlife. 
The trends in soil residues were few. With the exception 
of certain metabolites, the residues in soils were rather 
stable. Soil residues alone are rather poor indicators of the 
dynamics of the residues in earthworms, and undoubtedly 
in other soil fauna, that might be consumed by vertebrate 
species. The earthworm residues varied with a definite 
pattern coinciding with the periods of earthworm activity. 
Because earthworms use a larger area, both laterally and 
vertically, than would be represented by a single soil sam- 
ple, they probably are better indicators of the insecticide 
residues in the terrestrial environment than are single or 
pooled soil samples. 
Acknowledgments 
We are indebted to numerous colleagues and assistants 
who aided in either construction and maintenance of the 
plots, procurement of the samples, or preparation and 
analysis of the samples. E. J. Koch and R. G. Heath pro- 
vided valuable suggestions on statistical matters; G. E. 
Gates, Bangor, Maine, identified the earthworms. Provi- 
sion of the technical heptachlor by Velsicol Chemical Cor- 
poration also is gratefully acknowledged, 
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