20 Scientific American, November 2019ADVANCES
BIOLOGYHatchlings
with Vision
Jumping spider babies are
the size of a grain of sand
but see surprisingly wellAdult jumping spiders are littler than
a fingernail, but their vision is as clear
as a small dog’s. And the babies, with
heads a hundredth the size of their par-
ents’, may see in almost as much clarity.
Researchers have now discovered a
mechanical secret behind this remarkable
hatchling ability.
“Even arachnophobic people find these
little jumping spiders to be compelling—
they dance, they sing vibratory songs to
each other,” says Nathan Morehouse, a co-
author of the study published in July in
Vision Research. (Morehouse started the
research at the University of Pittsburgh
and finished it at the University of Cincin-
nati.) And the spiders’ extraordinary visual
ability captivates many scientists.
“Everyone I know who works on vision
just loves jumping spiders,” says Jamie
Theobald, who studies insect vision at
Florida International University and was
not involved in the new study. “How they
accommodate such amazing visual behav-
iors is a pretty important question.”
Researchers have observed that young
jumping spiders can use complex visual
cues while hunting. To find out how young-
sters’ vision is so close to adults’, More-
house and his colleagues peered into one of
the spiders’ four sets of eyes (a forward-fac-
ing, motion-sensitive pair) in 22 individuals
using a micro-ophthalmoscope, a miniature
version of an eye doctor’s tool.
The researchers counted
roughly 7,000 photoreceptorcells per eye in early juvenile, late juvenile
and adult spiders. They also examined sev-
en of the spiders twice, four months apart,
and found that none of them produced
new photoreceptors.
That measurement indicates the spi-
ders do not add receptors as they grow
but cram in all these cells by the time they
hatch—“Which is a crazy thing to do!”
Morehouse says. According to the team’s
earlier genetic research, the tiny spiders
most likely share an “ancient genetic tool
kit” with insects: their bodies first con-
struct the photoreceptors, then top them
off with lenses. That mechanism makes
sense for certain insects that add new pho-
toreceptors, capped with separate lenses,
to their eyes as they grow larger. But it is
developmentally cumbersome for spiders,
whose eyes each accommodate only one
lens and so need all their photoreceptors in
place early in life.
These results suggest spiderlings see as
much detail as adults, with a comparable
field of vision—although there are draw-
backs. For instance, baby spiders’ tiny pho-
toreceptors provide poor light sensitivity.
Morehouse has seen evidence of this him-
self: “They’re a little bit stumbly,” he says.
The eyes’ biological structure cannot
tell scientists everything about how the
spiders see. “They may be making trade-
offs at the neural level,” Theobald says,
such as restoring some sensitivity at the
expense of spatial or temporal detail. For
that reason, behavioral studies are neces-
sary to fully understand spiders’ vision. But
the biological results alone are surprising,
Theobald says: “To have to have all your
photoreceptors right from the beginning?
It’s not the way I would build a spider.”
—Leila SlomanAdult female
and spiderling
Phidippus audaxDANIEL ZUREKMorehouse Lab© 2019 Scientific American20 Scientifi c American, November 2019ADVANCES
BIOLOGYHatchlings
with Vision
Jumping spider babies are
the size of a grain of sand
but see surprisingly wellAdult jumping spiders are littler than
a fi ngernail, but their vision is as clear
as a small dog’s. And the babies, with
heads a hundredth the size of their par-
ents’, may see in almost as much clarity.
Researchers have now discovered a
mechanical secret behind this remarkable
hatchling ability.
“Even arachnophobic people fi nd these
little jumping spiders to be compelling—
they dance, they sing vibratory songs to
each other,” says Nathan Morehouse, a co-
author of the study published in July in
Vision Research. (Morehouse started the
research at the University of Pittsburgh
and fi nished it at the University of Cincin-
nati.) And the spiders’ extraordinary visual
ability captivates many scientists.
“Everyone I know who works on vision
just loves jumping spiders,” says Jamie
Theobald, who studies insect vision at
Florida International University and was
not involved in the new study. “How they
accommodate such amazing visual behav-
iors is a pretty important question.”
Researchers have observed that young
jumping spiders can use complex visual
cues while hunting. To fi nd out how young-
sters’ vision is so close to adults’, More-
house and his colleagues peered into one of
the spiders’ four sets of eyes (a forward-fac-
ing, motion-sensitive pair) in 22 individuals
using a micro-ophthalmoscope, a miniature
version of an eye doctor’s tool.
The researchers counted
roughly 7,000 photoreceptorcells per eye in early juvenile, late juvenile
and adult spiders. They also examined sev-
en of the spiders twice, four months apart,
and found that none of them produced
new photoreceptors.
That measurement indicates the spi-
ders do not add receptors as they grow
but cram in all these cells by the time they
hatch—“Which is a crazy thing to do!”
Morehouse says. According to the team’s
earlier genetic research, the tiny spiders
most likely share an “ancient genetic tool
kit” with insects: their bodies fi rst con-
struct the photoreceptors, then top them
off with lenses. That mechanism makes
sense for certain insects that add new pho-
toreceptors, capped with separate lenses,
to their eyes as they grow larger. But it is
developmentally cumbersome for spiders,
whose eyes each accommodate only one
lens and so need all their photoreceptors in
place early in life.
These results suggest spiderlings see as
much detail as adults, with a comparable
fi eld of vision—although there are draw-
backs. For instance, baby spiders’ tiny pho-
toreceptors provide poor light sensitivity.
Morehouse has seen evidence of this him-
self: “They’re a little bit stumbly,” he says.
The eyes’ biological structure cannot
tell scientists everything about how the
spiders see. “They may be making trade-
off s at the neural level,” Theobald says,
such as restoring some sensitivity at the
expense of spatial or temporal detail. For
that reason, behavioral studies are neces-
sary to fully understand spiders’ vision. But
the biological results alone are surprising,
Theobald says: “To have to have all your
photoreceptors right from the beginning?
It’s not the way I would build a spider.”
—Leila SlomanAdult female
and spiderling
Phidippus audaxDANIEL ZUREKMorehouse Labsad1119Adva3p.indd 20 9/18/19 5:19 PM
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