Why are so many spring flowers yellow, with other colours (such as blues and reds) appearing later?
Mike Follows
Sutton Coldfield, West Midlands, UK
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The first flowers of spring are often white or yellow due to what pollinates them: a broad range of insects, including flies. Flies don鈥檛 have colour perception, so they are attracted to contrast, and light colours stand out better against green foliage.
Though perhaps apocryphal, it is said that John Hertz, famous for starting the Yellow Cab Company in 1915 (and his subsequent eponymous car-hire business), decided on the iconic yellow colour for his cabs as a result of a survey he commissioned, which suggested that yellow is the colour most easily seen at a distance. Perhaps this also applies to pollinating insects.
Yellow pigment is also cheaper to produce, in energy terms, than other colours. Perhaps some species of plant have evolved to take advantage of this to get their billboards out early.
Hazel Russman
London, UK
Yellow flowers attract butterflies, which are some of the first insects to come out in spring, after hatching from overwintering chrysalises. Blue flowers are actually not far behind (think of yellow and blue crocuses). They have evolved to attract bees, as blue is in the middle of a bee鈥檚 visual spectrum. But it takes a little while longer for a hibernating beehive to wake up properly.
A 飞补蝉辫鈥檚 nest only comes fully on stream in high summer, as it starts from a single queen. Wasps have powerful jaws to cut up other insects for their carnivorous young, and this also allows them to pierce the skins of soft fruits and steal their sweet juices.
Since most fruits advertise their ripeness to passing birds by turning from green to red, wasps have developed optical receptors for red light (which bees lack). And some flowers seem to have taken advantage of this.
David Muir
Edinburgh, UK
At least in Europe, bumblebees are the first pollinators that people tend to notice in early spring. Usually this is the buff-tailed bumblebee, Bombus terrestris, which I have seen around Edinburgh in mid-February. But there are unnoticed pollinators buzzing around before B. terrestris; these are flies, and they provide their pollinating services to early spring flowers. Flies have poor colour vision but can differentiate light and dark, so they are attracted to the white and yellow flowers that brighten our late winter days.
Co-evolution is often thought of as a selective evolutionary pressure between two species. But there is also multi-species or diffuse co-evolution. This is where a number of similar species (in this case flies) develop a trait in reciprocity with traits in another group of species (white and yellow flowers), resulting in a mutual symbiosis. Flies better attracted to bright yellows and whites feed better, so they are more able to pass on their genes. And flowers that are more attractive to flies benefit from enhanced pollination.
Peg McCann
St Joseph, Michigan, US
As with so much in life and in science, the answer depends on what is meant by 鈥渟o many鈥�. The photo of garden beds full of daffodils that accompanied this question illustrates the quick answer: among spring-flowering garden plants, daffodils are common, mainly yellow and large. They also persist decades after planting, at least here in Michigan. An abandoned house may crumble with time, but the daffodils around it remain.
Another way to answer the question defines 鈥渟o many鈥� by number of species. Years ago, I used some US wildflower guides to tally each species by bloom colour and month. Species with white or whitish flowers generally bloom a few weeks earlier than those with yellow flowers. I also found that the number of species in bloom with blue flowers is about constant from May to September. Habitat may explain part of this. As many will have noted, plants in wooded areas bloom earlier (before the tree canopy closes) than plants in open spaces, and plants in wooded habitats have disproportionately pale blooms.
Simon Mitchell
London, UK
I read this question last week with bemusement as I looked out at the purple crocuses in my garden. Today, after a night of carnage instigated by our local grey squirrels, I no longer have any crocuses. I instead look out over the emerging yellow daffodils that it seems the squirrels dislike the taste of.
Next year I will only plant yellow daffodils, as I expect many gardeners have learned to do the hard way.
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