ah, to be a bee…

If we could see the flowers as bees see them they would be even more beautiful and varied!

Richard Feynman [The Feynman Lectures on Physics, Vol. I, Chap. 36, “Mechanisms of Seeing.”]

“Colour is what we perceive after our brains have processed visual information and represents the wavelength of light coming from objects. This is an important point – what you see is what you perceive not simply what the eyes sense. Sensation is the purely physical phenomenon whereby a sensor converts stimulus energy from the environment, such as light, into encoded electrical signals in the nervous system. What you perceive is the result of the nervous processing of these signals in the retina and brain as they are presented to the conscious. We can never know what an insect perceives, but we can ascertain how its sensors work and how the nervous system manipulates and modifies this information. We can never know whether or not an insect perceives colour in the way that humans do. What we can ascertain is whether or not they see and respond to colour.”1

Different species have vision adapted to the necessities of their living conditions. “Colour vision is an advanced feature. Your primate ancestors probably evolved colour vision as an aid to finding fruit in trees, since fruit was a staple part of their diet. Many birds and some fish also have colour vision, indeed their colour vision may exceed that of humans in terms of the variety of colours they can see. ” 2

“All mammals have rods and cones in their retinas (the light sensing lining of the back of our eyes). The rod cells are more sensitive to movement whereas the cones are more sensitive to light. Humans have more cones than dogs and cats, which is how we can detect a broader range of the light spectrum. (Though this is an oversimplification, of course.)”3
“Cats’ eyes have similar light wavelength absorption, although the colors are likely not as rich or vibrant as what we can see. This may be because they have better night vision than we do. Dogs’ eyes can only absorb blue-violet and red wavelengths of light, so their color vision is more limited.”4 
“[..]dogs see colors, but in dogs, the range of these colors is restricted to those in the yellow portion of the spectrum. They have a harder time distinguishing between red, yellow, green, and orange (albeit better in bright light). And they’re less likely to discriminate between hues of grays.” 5

“A zebra would never attract mates with a bright show of colours, but a bird might (apart from which birds can fly away from predators that may spot their bright colours whilst a zebra can’t!). The colour vision of birds also explains why insects need authentic camouflage colours to avoid being spotted by their avian predators, hence many insects are coloured in shades of green, yellow or brown. Many insects also advertise their bad taste or toxic make-up or stinging ability to would-be predators by having contrasting stripes, as in bees and wasps. The birds will see the stripes and their colours, whilst most mammals will see the contrasting stripes as shades of grey.”6

“The visible spectrum, light wavelengths from violet to red, is the light that typical humans can see. Typical “humans have sensors in the retina that respond best to blue light (440 nm, actually blue-violet), or best to green light (545 nm) or to red light (actually to yellow, orange and red light) a fourth type of sensor sees only shades of grey, black and white (it is achromatic). Most real colours are a mixture of red, green and blue. […] The whole spectrum of hues that humans can see is generated by blending these three primary colours: red, green and blue. For this reason, humans have trichromatic colour vision (trichromatic literally means ‘three-colour’). People who are colour-blind, however, are usually dichromatic (they can only see two colours) although some people may be totally colour blind and able to see only shades of grey. Most birds and goldfish and a few humans are tetrachromatic (they can see four primary colours) and some birds may be pentachromatic (they can see five primary colours) and so are capable of seeing more hues than your average human. “7

The spectrum of colors visible to insects is a little higher in frequency than what we humans can see. The lowest frequency of color we see, red, is invisible to insects.

“The insect compound eye is designed very differently to the vertebrate eye. The insect eye has much poorer spatial resolution, due to its design constraints, but some have much higher temporal resolution. Like mammals, insects can adapt to see in low light levels at night, and like primates and birds, at least some of them can see colour. Most insects can also see ultraviolet light (whether as a colour or as shades of grey) which helps them to navigate using the Sun. “8

The symbiotic relationship between flowers and butterflies has evolved so that flowers encourage butterflies and other pollinators to feed on their nectar. Plants attract potential pollinators in many ways, including by their color, scent, reflectance, size, outline, surface texture, temperature, and motion. In contrast, plants that do not depend on insect or bird pollination are unlikely to have showy or scented flowers.

“When teaching about insect vision, it is important to also emphasize that “flowers have evolved to the eyes of the insect” and not the other way around. Insects predate flowers by over 100 million years. The coevolution with pollinating insects (such as bees) results in the flowers reproducing best when they signal only to their target pollinators in the colors they see. These signals appear as bullseye-like patterns of many flowers. Red light, often invisible to insects, is used by flowers to attract pollinating birds such as humming birds.”9

The Floral Reflectance Database (FReD) was created by researchers at Imperial College London and Queen Mary, University of London, offering a glimpse in how bees and other pollinating insects may be seeing flowers.

“This research highlights that the world we see is not the physical or the ‘real’ world – different animals have very different senses, depending on the environment the animals operate in. [..] Much of the coloured world that’s accessible to bees and other animals with UV receptors is entirely invisible for us.”10

“We hope this work can help biologists understand how plants have evolved in different habitats, from biodiversity hotspots in South Africa to the cold habitats of northern Europe. [..] FReD’s global records may show how flower colour could have changed over time, and how this relates to the different insects that pollinate them, and other factors in their local environment.”11

Featured photographs are work of the photographer Craig P. Burrows, who employs photography method called ultraviolet-induced visible fluorescence that uses high-intensity UV lights to excite fluorescence found in some plants (and animals, and various objects), offering a glimpse of how (possibly) these flowers look through the insects’ eyes.

Photographs by Craig P. Burrows, website and Flickr

References:
1 Insect vision [https://cronodon.com/BioTech/Insect_Vision.html]
2 ibid
3 Dr. Khuly, P. “Colorblindness and Vision in Pets: Are Dogs And Cats Color Blind?”
4 Dr. Brister, J. “7 Eye-opening Cat and Dog Eye Facts“
5 Dr. Khuly, P. “Colorblindness and Vision in Pets: Are Dogs And Cats Color Blind?“
6 Insect vision [https://cronodon.com/BioTech/Insect_Vision.html]
7 ibid
8 ibid
9 Lincoln, J. and Davidhazy, A (2019) Ultraviolet photography and insect vision, The Physics Teacher 57, 204; https://doi.org/10.1119/1.5092494
10 Arnold SEJ, Faruq S, Savolainen V, McOwan PW, Chittka L (2010) FReD: The Floral Reflectance Database — A Web Portal for Analyses of Flower Colour. PLoS ONE 5(12): e14287. https://doi.org/10.1371/journal.pone.0014287
11 ibid