nonin terfe rence fro m man, Nature can have her way, s etting up all that wonde rful and intricate
s ys tem of checks and balances that protects the fores t from undue damage by ins ects.
In the United States our foresters seem to have thought of biological control chiefly in terms of
introducing ins ect parasites and predators. The Canadians take a broader view, and some of the
Europeans have gone farthes t of all to develop the s cience of ‘fores t hygiene’ to an amazing
extent. Birds, ants, forest spiders, and soil bacteria are as much a part of a forest as the trees, in
the view of European foresters, who take care to inoculate a new forest with these protective
factors. The encouragement of birds is one of the firs t s teps. In the mode rn era of intens ive
fores try t he old hollow trees are gone and with them homes for woodpecke rs and othe r tree-
nes ting birds. This lack is met by nes ting boxes , which draw the birds back into the fores t. Other
boxes are s pecially des igned for owls and for bats , s o that thes e creatures may take over in the
dark hours the work of ins ect hunting performe d in daylight by the s mall birds.
But this is only the beginning. Some of the mos t fas cinating control work in European fores ts
employs the forest red ant as an aggressive insect predator—a s pecies which, unfortunately,
does not occur in North Ame rica. About 25 years ago Professor Karl Gösswald of the University
of Würzburg develope d a method of cultivating this ant and es tablis hing colonies. Under his
direction more than 10,0 00 colonies of the red ant have been es tablis hed in about 90 tes t areas
in the German Fede ral Republic. Dr. Göss wald’s method has been adopted in Italy and other
countries , where ant farms have been es tablis hed to s upply colonies for dis tribution in the
forests. In the Apennines, for example, several hundred nes ts have been set out to protect
reforested areas. ‘Where you can obtain in your fores t a combination of birds ’ and ants ’
protection together with s ome bats and owls , the biological equilibrium has already been
essentially improved,’ says Dr. Heinz Rupperts hofe n, a fores try officer in Mölln, Germany, who
believes that a single introduced predator or parasite is less effective than an array of the
‘natural companions ’ of the trees.
New ant colonies in the fores ts at Mölln are protected from woodpecke rs by wire netting to
reduce the toll. In this way the woodpeckers , which have increas ed by 400 per cent in 10 years
in s ome of the tes t areas , do not s erious ly reduce the ant colonies , and pay hands omely for
what they take by picking harmful caterpillars off the trees. Much of the work of caring for the
ant colonies (and the birds ’ nes ting boxes as well) is ass umed by a y outh corps from the local
s chool, children 10 to 14 years old. The cos ts are exceedingly low; the benefits amount to
permanent protecti on of the fores ts. Another extremely interesting feature of Dr.
Rupperts hofen’s work is his us e of s piders , in which he appears to be a pionee r. Although there
is a large literature on the classification and natural history of spiders, it is scattered and
fragmentary and deals not at all with their value as an agent of biological control. Of the 22,000
known kinds of s piders , 760 are native to Germany (and about 2000 to the United States ).
Twenty- nine families of spiders inhabit German forests. To a fores ter the mos t important fact
about a s pider is the kind of net it builds. The wheel-net s piders are mos t important, for the
webs of s ome of them are s o narrow- mes hed that they can catch all flying ins ects. A large web
(up to 16 inches in diamete r) of the cros s s pider bears s ome 120,000 adhes ive nodules on its
s trands. A s ingle s pider may destroy in her life of 18 months an average of 2000 insects. A
biologically s ound fores t has 50 to 150 s piders to the square meter (a little more than a square
yard). Whe re there are fewer, the deficiency may be remedied by collecting and dis tributing the
baglike cocoons containing the eggs. ‘Three cocoons of the was p s pider [which occurs als o in
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