Skip to main content
fresh garden vegetables

Edible Gardening Series: Question of the Week – Insect vision and colors

By Carol Wyatt-Evens and Sarah Bostick

Gardening in Florida can be incredibly rewarding and incredibly frustrating at the same time. If you are new to the region, you soon learn that gardening in the sunshine state can quickly become a full-time job. Our subtropical climate is perfect for growing an abundance of different vegetables, fruits, and herbs, but the challenges can sometimes be a bit overwhelming.

We can help!

Agents from UF/IFAS Extension Sarasota County have partnered to offer a weekly, 30-minute workshop on Zoom to help answer your gardening questions. The first 10 minutes offers an educational component relevant to the urban gardener. The remainder of the time is dedicated to question and answer – any question you have! The series runs through the second week in May 2021 with the exception of holidays. You must register for the series on Eventbrite to receive the link to the series. You only need to register once to get access to the entire series:

Edible Gardening Series

Every week, the agents will post a question from the webinar that we are sure will be helpful for our community gardeners at large.


Question of the Week:

How do insects see?

Insects use their eyes in much the same way as humans do – to navigate, find food, and interact with the world around them. Sight is also used to help them find mates. insect eyes and human eyes are similar in that both have lenses and photoreceptors, but overall, the two are quite different.

The human eye consists of a single lens. The muscles of the eye allow it to move freely in the eye socket but can only look in one direction at a time. An insect’s compound eye has many lenses, but the eye is fixed. Insects, such as a predatory dragonfly, can have up to 30,000 lenses per eye. This is like having 30,000 tiny eyes looking in different directions! Each individual lens in the insect eye is part of a structure called an ommatidium. These structures are clustered together like a pack of drinking straws and collectively make up the insect compound eye. But, insects with compound eyes also have another type of eye that helps them ‘see’. These are the three simple eyes, ocelli, that are found on the top or at the front of the head in a triangle pattern. Ocelli are simple photoreceptors (light-detecting organs) that help the insect see shadows, see light and dark, detect movement, and orient themselves toward a light source (usually the sun).

damselfly compound eyes

damselfly compound eyes [photo credit: Pixabay]

dragonfly compound eyes

dragonfly compound eyes [photo credit: Pixabay]

Ocelli or simple eyes at top of hornets head

Ocelli, or simple eyes, of an asian hornet [photo credit: Alan Smith-Pardo,USDA APHIS_PPQ, Bugwood.com]


Wavelengths and Color

The human eye has an iris that adjusts the amount of light entering the eye, allowing the eye to focus on objects with crisp detail. Insect eyes lack that light-adjusting ability and the end result is a fuzzy or out-of-focus image. With insects, the greater the number of ommatidia, the better the visual acuity or quality. However, even insects eyes with 30,000 lenses will never be able to ‘see’ objects the same way as a person. Life will always appear a bit fuzzy to an insect.

So, how do insects see color compared to humans? It’s all about wavelengths.

electromagnetic spectrum

the wavelength of visible light along the electromagnetic spectrum

The visible spectrum, that spectrum with a famous name, ROY G. BIV, (red, orange, yellow, green, blue, indigo, violet) has a wavelength range from 700 nanometers (nm) for red to 400nm for violet. The visible light spectrum is part of the electromagnetic spectrum – a very small part – but the segment on the spectrum that corresponds to colors.


Insects and Ultraviolet Light

Humans see the entire visible spectrum from red to violet, but insects see from 650nm to 300nm. Yes, that is off the chart! Insects have the ability to see in the ULTRA-violet (UV) range on the spectrum. The range with higher frequency, shorter wavelength, and beyond where humans are capable of seeing. Within this spectrum, the colors that insects see really well are ultraviolet, green, and blue. They have difficulty seeing yellow and orange and they cannot see the color red at all.

When it comes to which wavelength insects are most attracted to – it’s ultraviolet (UV) light. People have taken advantage of insect attraction to UV light to eliminate insects around their home and yards. We use ‘bug zappers’ to kill unsuspecting insects that like to bite and suck our blood.

bug zapper using Ultraviolet lightbulbs

UV light bug zapper [ photo credit: Pixabay]

These ‘zappers’ use UV light-emitting bulbs (a UV lightbulb or a black light) to attract insects to the contraption, only to be zapped to death when they come in contact with the wire frame surrounding the lightbulbs. Unfortunately, the number of biting insects (mosquitoes) killed by these zappers is extremely low compared to the number of non-biting or beneficial insects killed by the device.

 

Flower Power

Flowers also take advantage of ultraviolet light to attract a specific group of insects – pollinators. Flowers use patterns in their petals that act like a bullseye for the pollinators. The insects get a tasty meal while helping the flowers by moving extra pollen to the next flower. The flower pattern may not be obvious to us, but under UV light the pattern on the petals glows like a neon arrow directing the insect to the pollen.

flower under ultraviolet and infrared light

Flower under natural light, ultraviolet light, and infrared light [photo credit: Pixabay].


Insects and the Color Yellow

Besides UV light, we also take advantage of colors to both attract and repel insects. Since yellow is at the far edge of the insect sight range, we use yellow lightbulbs outside our homes to keep from attracting insects.  However, this will not completely eliminate insects since some light wavelengths in the blue range will still be emitted, a few insects will still be drawn in. To fully eliminate any insect attraction, red lightbulbs can be used. Unfortunately, red doesn’t offer our human eyes much usable light. It is very dim lighting and not very useful as a lighting source.

yellow sticky card in a shade house

Yellow sticky card [photo credit: David Goehring, Flickr]

Another way we use yellow is in the garden and landscape with yellow sticky traps. Now, I know, it seems counter to what has been said – they cannot see yellow. Yellow is a bright and very reflective color -it is very good at reflecting UV light. The yellow sticky card acts much like the patterned flower and will draw the insect toward the source emitting the UV light. In this case, to an unfortunate end for the insect, since the perceived light source is a yellow sticky trap.

Factsheets and resources: 

The Edible Gardening Series and blog series is a partnership between the following UF/IFAS agents and Sarasota County staff:

2 Comments on “Edible Gardening Series: Question of the Week – Insect vision and colors

  1. It’s so sad to read how the zippers kills more non biting and beneficial insects than mosquitoes.

    • Hi Gustavo,
      I agree 100%! It is very sad, but I don’t think people do it out of dislike for insects. I think it is wanting to rid their home of a specific insect – mosquitoes. We need to understand how and why outdoor lighting attracts insects in the first place. People would benefit by changing the existing lightbulbs to LED bug lights. It would be 100% safer for our beneficial arthropods as well as reduce electric cost and light pollution! An added benefit is that it would also eliminate the frog and lizard frass found around the light since it’s the insects that attract the predators in the first place. Hopefully, this blog will shed a little light on the subject!

Leave a Reply

Your email address will not be published. Required fields are marked *