8 February 2020 | New Scientist | 43Arachnid intelligence is challenging our ideas about
brains and consciousness – and their minds may even
stretch into their webs, finds David Robson
>To construct an orb
web, a spider must be
capable of foresight
and planning
T
HERE is an alien intelligence living
among us. These creatures possess an
extraordinary kind of consciousness,
including minds that extend beyond their
bodies. Yet, thanks to our ignorance and
arrogance, our immediate impulse is to
kill them.
This is no fantasy. These alien minds really
are lurking in the shadows of our houses and
gardens: spiders. We have long assumed that,
like many invertebrates, they are little more
than automata, lacking an inner life. But we are
now discovering that some arachnids possess
hidden cognitive abilities rivalling those of
mammals and birds, including foresight and
planning, complex learning and even the
capacity to be surprised. Stranger still, the
delicate silk threads they spin out behind
them, so easily swept up by a feather duster,
help them to sense and remember their world.
Indeed, spiders’ silk is so important to their
cognitive abilities that some scientists believe
it should be considered part of their mind.
Now that we are starting to appreciate
spiders’ intellectual capabilities, we must
surely change how we see one of the most
ubiquitous, important and vilified groups
of animals that has ever evolved. What’s
more, these incredible creatures could also
challenge our understanding of our own
intelligence and minds.
Spiders have deep evolutionary roots.
spiders, says Arnedo. But their intelligence will
have been critical, too. The best evidence of
spider smarts is found in the everyday activity
of web building. Around a third of all species
make orb webs, those beautifully geometrical
deathtraps hanging in our houses and gardens.
They hold more secrets than Charlotte’s Web,
because each is a record of the decisions taken
during its construction.
Consider the basic question of where to
build the web. Every species of orb web spider
has a preferred size and shape of web to suit its
body type and prey, but individuals tailor their
constructions to fit into restricted spaces or
around obstacles. This suggests that before
building begins, some kind of planning takes
place. That is particularly impressive when
you consider that most spiders are almost
completely blind. How do they do it?
One possibility, according to Thomas
Hesselberg at the University of Oxford, is
that they use their silk as a kind of plumb
line to scout out a potential web site. When
exploring, some spiders first cast a horizontal
line between two surfaces and then traverseThe earliest fossil evidence of silk-producing
arachnids dates from almost 400 million years
ago, shortly after the first definitive evidence
of insects. “Insects are the most successful
lineage on Earth, but spiders pretty much
follow them,” says evolutionary biologist
Miquel Arnedo at the University of Barcelona,
Spain. Today, there are more than 48,000
known species, with every square metre
of land home to around 130 individuals on
average. That may terrify arachnophobes,
but without them, agriculture would be
impossible. “You couldn’t have any crops –
insects would eat them all,” says Arnedo.
Spiders are defined by their eight legs and
intricate spinnerets, which extrude silk. This
is a protein made up of chains of amino acids,
primarily glycine and alanine, that spiders
extract and comb with their back legs to
strengthen it. Some species can produce
fibres with different chemical compositions
depending on their particular need.
Spider silk – the envy of human engineers – is
put to a huge range of uses, including building
cocoons, windsurfing and as a rope for
climbing and abseiling. Many spiders also use
it for a sort of^ “flight” known as ballooning,
in which a few threads, lifted by electrostatic
forces in the atmosphere, carry them far and
wide on nothing more than a light breeze.
These species detect these forces with hairs
on their legs, allowing them to decide when
to put up their “sails”. “They can feel the change
in the air,” says Erica Morley at the University
of Bristol, UK, who made this discovery.
The sheer versatility of their silk helps
explain the enormous evolutionary success of“ Webs are like
instruments that
spiders carefully
‘tune’ according to
their experiences”