|Praying mantises are the only invertebrates known to see in 3D. The
predatory insects excel at detecting prey that comes within striking
distance, but-unlike us-their depth perception only works when the prey
is moving. How do we know this?
In a new study, scientists from the University of Newcastle in Britain
glued the world's tiniest 3D glasses on 20 praying mantises and showed
them a series of movies depicting patches of moving dots, potential
'prey items', camouflaged against a matching background. The insects
tried to catch 'prey' that appeared to be within 2.5 centimetres of
their perch. And they could still do it even when the 'prey' item, or
dot configuration, looked completely different to the two eyes,
something that people found challenging when they were asked to perform
the same task.
Humans see in 3D by stitching together the actual image coming in from
one eye versus the other, but this work shows that praying mantises only
bother stitching together the motion, the actual image doesn't matter to
them. It is the first time this kind of 3D vision has been found in
nature, and it is yet another example of evolution coming up with
different solutions to the same problem, in this case, when to strike at
a passing fly.