Ju­nior gar­den­ers

The way bees see is their su­per­power. Their unique vi­sion gives them the abil­ity to find nec­tar- and pollen-rich flow­ers.

NZ Gardener - - CONTENTS -

How bees see

Bees have two dif­fer­ent types of eyes

which do dif­fer­ent jobs. On top of their heads are three small, sin­gle-lensed eyes called ocelli. Bees use them to see flower colours with ul­travi­o­let light, judge light in­ten­sity, nav­i­gate and keep ori­en­tated.

They also have two much larger com­pound eyes with thou­sands of facets or tiny lenses. Each facet is con­nected to a cone with eight cells called pho­tore­cep­tors. In each cone, there are two re­cep­tors for each of the colours blue, yel­lowy-green and ul­travi­o­let. In­for­ma­tion from all the facets is col­lated by the bee’s brain and makes a mo­saic pic­ture of its sur­round­ings. It sounds com­pli­cated but it’s amaz­ingly fast. Bees per­ceive colour three to five times faster than hu­mans. This means they can see in­di­vid­ual flow­ers blow­ing in the wind even while fly­ing.

Hu­mans also have three sorts of pho­tore­cep­tors but ours de­tect red, blue and green. Bees can’t see red be­cause they don’t have the right re­cep­tors, but they do see ul­travi­o­let mark­ings on petals that are in­vis­i­ble to hu­mans.

Plants have evolved to ex­ploit the way bees see. Flow­ers pol­li­nated by in­sects have con­trast­ing colours that stand out from fo­liage around them. In con­trast, wind-pol­li­nated flow­ers are of­ten sim­i­lar in colour to leaves and stems as they don’t need to be de­tected by sight. Flow­ers that rely on bees have ul­travi­o­let mark­ings on the petals around the pollen-rich sta­mens and nec­taries which pro­duce nec­tar. Bees are quick learn­ers. They as­so­ciate the mark­ings with food so go straight for the ul­travi­o­let bull’s-eye blotches and lines that lead to the sweet nec­tar within.

Bees also de­tect the pat­terns of po­larised light in the sky and use them to find their way back to the hive even if the sun isn’t shin­ing and at dif­fer­ent times of the day.

A bee that has found a good source of nec­tar or pollen can let the other for­ag­ing bees know where to go. If the food is within 50-100m of the hive, the bee does a round dance, quickly turn­ing clock­wise and anti-clock­wise and the sur­round­ing bees fol­low along.

If the food is fur­ther away, the for­ag­ing bee does a wag­gle dance, turn­ing in a semi-cir­cle then go­ing back to the be­gin­ning wag­gling her ab­domen. The an­gle gives in­for­ma­tion about the di­rec­tion of the food and the time go­ing across the cir­cle gives the dis­tance.

Evening prim­rose in ul­travi­o­let light.

Evening prim­rose in vis­i­ble light.

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