Bumblebees and poppies: do they see red?

 Human colour vision allows us to see a spectrum of colours that extends from violet to red - the colours of the rainbow - but bumblebees' colour vision is different. They can see ultraviolet, at the short wavelength end of the spectrum, but don't perceive the colour red at the long-wavelength end. But they are constant visitors to scarlet poppies in my garden, so there must be another cue that attracts them from a distance. My guess is that the lure must be a chemical one, a scent that they can detect but we can't, although the contrasting dark whorls of stamens in the centre of the flower would also  be visible to the visitor once they are close enough to see inside the flower. 

I watched this bumblebee make multiple attempts to find its way into the poppies waving in the wind, and once it found its way inside I could hear it buzzing, to shake pollen from the mass of stamens in the centre of the flower. You can see the bluish-grey poppy pollen packed into pollen baskets on its hind legs in these photographs.

Red Admiral hairy eyes

One of the pleasures of macrophotography is that you tend to notice things in the captured image that you'd never be aware of otherwise.

Until the colder weather arrived a couple of days ago we had several red admiral butterflies in the garden. I took some extreme close-ups of them, while they were feeding on ripe pears, and noticed in the images .....

.... that their eyes have this strange hexagonal pattern. Looking closer still, it's clear that .....

.... the eye surface is hairy and it looks like it's the pattern of hairs, located in between the individual ommatidia of their compound eyes, that is responsible for those large pale hexagons. A comparison with eyes of other common butterflies, like...

..... this small white, shows a pattern of darker patches on the eye but not a hint of hairiness around the ommatidia.

So I wonder what the hairs' function might be? Maybe they enhance flicker vision - the sensitivity of compound eyes to movement of objects across the field of vision............? 

Hairy eyes are not uncommon in insects - click here, for example, to see a scanning electron micrograph of a honeybee's hairy eye. Another possibility of that the hairy surface might stop pollen sticking to the eye surface in these flower-visiting insects.........

Eye-to-eye with a fly

I haven't managed to identify the species that this fly belongs to yet, but it does have beautiful eyes.......

For Our Eyes Only?

The first lesser celandines are coming into flower around here and it's a delight to see their glossy yellow flowers. One of the fascinating things about the flowers that we find so aethetically appealing is that the natural selective forces that have produced their colours throughout their evolutionary history have nothing to do with human vision and everything to do with the way that insects see the world. Many insects can perceive short wavelength ultraviolet radiation, that is invisible to us, but can't see as far as us into the long wavelength, red end of the spectrum. To grasp the implications of this it's useful to consider the colour purple, which is a combination of the extreme ends of the colour spectrum that we can see - blue and red. For an insect that can see shortwave ultraviolet radiation but can only see as far as yellow into the longer wavelength end of the spectrum the combination of these extremes is a colour that we can only guess at. What is certain is that a yellow lesser celandine doesn't look yellow to many insects.

While we can't know exactly what colours an insect's eyes and nervous system perceives, we can get some idea of how flowers look at the ultra-violet end of the spectrum that bees and some butterflies can see. This is a celandine flower photographed in monochrome using old fashioned silver halide black-and-white film (remember that?), using white light (sunlight).
 
This is the same flower using a filter that only passes ultra-violet light that's reflected from the petal surface. Notice how the centre of the flower - the location of the stamens and stigmas - strongly absorbs UV and how the petals themselves reflect it. This hidden pattern of UV reflectance acts as a target, zeroing the insect in on the important parts of the flower once it picks up the reflected UV light from the petal tips. Photographing floweres using UV filters reveals all sorts of cryptic UV absorbing and reflecting patterns that insects can see but which are invisible to us.

You can see more examples of flowers viewed in a way that insects might see them here