A spider's unusually large and
sensitive eyes help it catch bigger prey
Date: May 18, 2016
Source: University of
Nebraska-Lincoln
Evolving the largest eyes among
all known arachnids may have helped the net-casting spider add walking prey to
its airborne menu of midnight snacks, says new research from University of
Nebraska-Lincoln biologists.
Doctoral student Jay Stafstrom
reached the conclusion after two months living out of a tent in a Florida state
park, where he observed how the nocturnal species Deinopis spinosa hunted
with and without the aid of secondary eyes roughly 2,000 times more
light-sensitive than human eyes.
The net-casting spider earns its
name by spinning a rectangular band of woolly silk to capture prey while
rappelling upside-down from a single thread. When the time comes, the spider
lunges forth and stretches the net to engulf prey in one fell swoop that lasts
about one-thousandth of a second.
Stafstrom discovered that the
spider snared prey about 3 1/2 times more often when relying on its massive
secondary eyes than when those eyes were covered by vision-impairing dental
silicone. But the effect seemed to depend on whether that prey traveled by leg
or by wing.
While the silicone had no
discernible effect on the species' ability to snag flying prey, it greatly
reduced the odds of the spider capturing a crawling critter. Though one of
every four specimens without the silicone blindfold would capture prey that
walked their way -- roughly the same proportion that caught prey flying through
their attack radius -- none managed to snare a walking meal while their vision
was impaired.
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