THE SPIDER POPULATION
IV. THE SPIDER POPULATION.
The earliest census recording the spider population of a stated area
was that made by McAtee (1907) near Washington, U.S.A. His
investigation was confined to 4 sq. ft. of ground in woodland and in
meadow. The density of the spider population was equivalent to
11,000 per acre of woodland and 64,000 per acre of meadow.*
In 1922 H. M. Morris's census of arable land at Rothamsted, which
was bare of vegetation except for a few weeds, yielded a spider
density of 20,000 to the acre. Of these, 75% were Linyphiids.
A recent investigation of grass plots at Rothamsted by W. Ladell
and K. D. Baweja yielded a density of 159,000 spiders per acre
after clipping away the grass to soil level. The results of this
investigation are contained in a thesis written by Baweja in 1937 for
his Ph.D. I have to thank the authorities at Rothamsted for permission
to see this document and Ladell for exact figures of the spider
captures. In contrast to Morris, whose sifting of the soil population
was done by hand, Ladell and Baweja employed a flotation process
for the separation of the invertebrates from the soil.
The density of the spider population of a clay meadow near Oxford
which had been untouched for three years was found by J. Ford (1935)
to be approximately 407,000. Like Ladell and Baweja he employed a
flotation process, but in contrast to them, he did not remove the
vegetation before counting the inhabitants. His results agreed with
those at Rothamsted and in Central Europe (Frenzel) in that the total
invertebrate population is higher in the
*McAtee's figures were 11 and 53 spiders respectively. The former, however, is shown to
include a mite and a pseudoscorpion, so this must be reduced to 9. The meadow census is not
analysed, so it is probable that this figure also contains Arachnids other than spiders.