Page 36 - Adventures through the World of Entomology

So much for insects’ antennae. Let’s now move to some other important organs on the head — the eyes. So much for insects’ antennae. Let’s now move to some other important organs on the head — the eyes.
Insects, in general, have two kinds of eyes. Insects, in general, have two kinds of eyes.

First there are the simple eyes, called ocelli. Some First there are the simple eyes, called ocelli. Some
insects do not have any ocelli. Some insects have insects do not have any ocelli. Some insects have
only one. Some insects have two and some insects only one. Some insects have two and some insects
have three. The Honeybee is an insect that has have three. The Honeybee is an insect that has
three ocelli, and a pair of compound eyes as well. three ocelli, and a pair of compound eyes as well.
The ocelli are arranged in the configuration of a The ocelli are arranged in the configuration of a
triangle. They consist of a simple dense lens with triangle. They consist of a simple dense lens with
some light receptors (sensory retinal cells) beneath some light receptors (sensory retinal cells) beneath
the lens. These eyes cannot focus and they cannot the lens. These eyes cannot focus and they cannot
produce images. They are there solely to perceive produce images. They are there solely to perceive
differences in light intensity. A quick change differences in light intensity. A quick change
in light intensity means danger to the insect and Photo Courtesy of UNVAR in light intensity means danger to the insect and Photo Courtesy of UNVAR
causes it to run or fly away. Have you ever tried causes it to run or fly away. Have you ever tried
to catch a fly with your hand and just as you were ready to swoop down on it, it flew away? Chances to catch a fly with your hand and just as you were ready to swoop down on it, it flew away? Chances
are, the shadow of your hand fell over its ocelli announcing the presence of danger. When termites are are, the shadow of your hand fell over its ocelli announcing the presence of danger. When termites are
swarming, if a shadow (perhaps from a small passing cloud) passes over the exit tube, the termites will swarming, if a shadow (perhaps from a small passing cloud) passes over the exit tube, the termites will
stop their swarming and perhaps that colony will not put out any more swarmers that year. The danger stop their swarming and perhaps that colony will not put out any more swarmers that year. The danger
bell was rung! bell was rung!

The second kind of eyes that insects have are the compound eyes. These are much larger and sometimes The second kind of eyes that insects have are the compound eyes. These are much larger and sometimes
take up a large part of the surface of the head. A single insect may have both simple and compound take up a large part of the surface of the head. A single insect may have both simple and compound
eyes. The surface of the compound eye is covered with hexagonal lenses – several thousand of them eyes. The surface of the compound eye is covered with hexagonal lenses – several thousand of them
– each focusing on an individual retina which produces a part of the scene before it. The central nervous – each focusing on an individual retina which produces a part of the scene before it. The central nervous
system integrates the signals from the individual lenses into a mosaic image. This type of eye is system integrates the signals from the individual lenses into a mosaic image. This type of eye is
particularly adapted to perceive movement, and here again, movement signals danger. The fly that you particularly adapted to perceive movement, and here again, movement signals danger. The fly that you
were trying to catch may have perceived the movement of your hand. were trying to catch may have perceived the movement of your hand.

HONEY BEE BALD-FACED HORNET HONEY BEE BALD-FACED HORNET

3 ocelli (siMple eyes) 3 ocelli (siMple eyes)

coMpounD eye coMpounD eye
Photo Courtesy of UNVAR Photo Courtesy of UNVAR Photo Courtesy of UNVAR Photo Courtesy of UNVAR
Honey Bees have 2 compound eyes and 3 Bald Face Hornets have 3 ocelli and 2 Honey Bees have 2 compound eyes and 3 Bald Face Hornets have 3 ocelli and 2
ocelli (simple eyes). compound eyes. ocelli (simple eyes). compound eyes.

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