Quick read: Three awesome vision features that insects have
Since I was a kid I was fascinated with insects, and my
favorite order of insect is, without a doubt, Mantodea (Praying Mantises). They
are amazing at camouflaging themselves, imitating plants, catching prey,
avoiding getting eaten by bigger animals, and much more. To add to all of that,
they have a super cool alien look and they come in an assortment of colors! There’s
so much to talk about when it comes to these intriguing creatures, but let’s
use this photo I took of a bush mantis (Sphodromantis viridis) as an
opportunity to discuss three cool vision features that they have and you might
have not known about:
1. The Ocelli
Three simple eyes that many insects have at the center of
their forehead (the number might slightly vary). They are very sensitive to
light, but don’t detect colors and shapes. Insects use these to determine the
time of day, to detect if they are being shaded by a large animal, and possibly
also for flight stabilization.
You can see it in this image between the antennas. Two of
the ocelli are very close to the bases of the antennas (closer to the center)
and the remaining ocellus is dead center.
2. The compound eye pigmentation change
Some arthropods can change the color of their compound eyes
when it gets dark. The eyes usually turn darker and red. This pigmentation
makes the eyes more sensitive to light, making them see better in the dark (I
always think of it as turning up the iso in a digital camera, making the sensor
more sensitive, but it might be more like getting more sensitivity on the
expense of resolution).
You can see that the Mantis in the photo has red eyes, but
if you’ll look at the same individual during the day with light around, you’ll
see a different color – light brown/green.
3. The Pseudopupils
Ever wondered about those black, pupil-like spots that
Mantids and other arthropods have? The ones that seem to “move around” as you
look at them from different angles?
Well, the name already suggests that these are not actual
pupils, so what are they?
Arthropods' compound eyes are made out of many
ommatidia, which have a Hexagonal prism shape.
Each of these ommatidia has a very narrow field of vision, but when combining
thousands of them, you can get to an almost full 360 degrees vision (As in
Dragonflies for example).
The black “pupil” you see, are actually the ommatidia that
are pointed directly at you and absorb all the light coming from your angle.
This means that if you thought these creatures keep looking
right at you, you were right! It’s only that they do it passively without the
need to actively move their eyes/body.
In the photo, you can see the ommatidia that are pointing
directly at the camera and appear as black spots on the compound eyes.
Want more info? You can start here:
Pigmentation
change in Mantids eyes (and more)