8 February 2020 | New Scientist | 45This is exciting because it means that spiders
could provide valuable information about
which neural structures are necessary for
conscious experience, as well as how these
evolved. In a vertebrate, the midbrain gathers
sensory information and bodily signals, then
integrates these to create a mental simulation
of the world and the creature’s place in it. This,
in turn, directs its attention and movement
according to its needs, creating an “experiential
consciousness” on which to build other types
of awareness, such as self-reflection. “It
basically underpins everything,” says Andrew
Barron at Macquarie University, Australia.
Invertebrate brains take a different form,
but a structure called the central complex
shows the same connectivity in insects,
argues Barron. In spiders, a region known as
the arcuate body may have the same purpose.
Detailed studies of spider brains have been low
on neuroscientists’ lists of priorities. However,
if further evidence supports the idea that these
regions create an inner representation of the
world, this could help us pinpoint a date for
the emergence of conscious experiences –
potentially more than half a billion years ago,
when the Cambrian explosion gave rise to
almost all the animal groups around today.
In the meantime, a greater appreciation
of spider smarts might give us all pause for
thought the next time we are confronted with
eight-legged squatters hiding in our hallways.
Written on their silken webs, we may one day
find clues to the origins of thought itself. ❚determine the structure of its web, which, in
turn, alters what it senses in its environment,
directly influencing its future decisions. As a
result, part of a spider’s memory and decision-
making is outsourced beyond its body.
Much as tool use has aided human success,
spiders might have evolved extended
cognition to help them survive and thrive
in varied environments. “Spiders have extra
selective pressure for evolving extended
cognition because of their relatively tiny
brains and their high cognitive requirements
as generalist predators,” says Japyassú.
Given the new discoveries, might we even
attribute consciousness to spiders? Most
researchers see consciousness as a spectrum,
ranging from a basic mental representation
of the surrounding environment and the
capacity to shift attention between elements,
to imagination, advanced self-awareness and
metacognition, the capacity to reflect on your
own judgements. Most invertebrates are
considered incapable of even the most basic
level of conscious experience, responding to
situations automatically instead. But spiders’
mental representation of space and their
capacity for foresight and planning appear
to reflect more complex inner experiences.
“We’ve seen that Portia are able to ‘think’
about what they are doing before actually
doing it,” says Cross.David Robson is the author
of The Intelligence Trap:
Revolutionise your thinking
and make wiser decisions“ Given spiders’
smarts, might we
even consider them
to be conscious?”
Portia even seem capable of being surprised.
In experiments similar to the previous one,
Cross and Jackson changed the type of prey
while it was out of sight of the spiders. This
led them to pause – a sign of confusion, often
used by psychologists to test what babies are
thinking. Portia also pause for longer if they
find more or fewer prey awaiting them at the
end of the path, compared with what they had
seen from their tower. That suggests these
spiders have a basic number sense.
Despite Portia’s catlike stalking style, silk is
still essential to their survival, and they often
employ it when hunting. They sometimes
build a web as a vantage point from which
to abseil onto prey, or as a means of catching
insects to use as bait for tasty spiders. Portia
also invade other spiders’ webs and pluck
the silk to mimic a trapped insect, drawing
occupants from their hiding places so they
can pounce and kill them. They seem to learn
the correct vibrations through trial and error.
Such findings, combined with new evidence
of spider sociability (see “Social webs”, left),
indicate advanced cognition across many
spider species. Yet the brains of these creatures
are often minute: most orb weavers, for
instance, weigh between 50 and 80 milligrams,
with some less than 1 milligram, and their
brains are just a fraction of that. Spiders’
ancient origins also raise some profound
philosophical questions about the evolution
of the brain. Previously, we have tended to
look for intelligence in our closer relatives,
but broadening the web to animals like spiders
has proved profitable. “The success of this line
of research shows that we should be careful
not to restrict our research questions or
study species,” says Caroline Strang at the
University of Texas at Austin, who investigates
insect cognition.
These findings have even caused us to
reconsider the definition of the animal “mind”.
Take the concept of extended cognition, an
idea that has been of particular excitement to
psychologists of late. Philosophers coined this
term to describe the way our tools become
incorporated in our thinking. We turn to a
notebook or smartphone, for instance, as an
external memory source that can be accessed
at will. In this view of cognition, our minds
extend beyond our brains to all the objects
that contribute to our perception, memory
and reasoning. Hilton Japyassú at the Federal
University of Bahia in Brazil and Kevin Laland
at the University of St Andrews, UK, have made
a strong case that a spider’s use of silk qualifies
as a natural example of extended cognition.
After all, a spider’s past experiences can
A dandy jumping
spider (far right)
lures its spider
prey by pretending
to be caught in
its webEMANUELE BIGGI/NATURE PICTURE LIBRARY