Flowers might produce nectar as a "brilliant distraction technique" to protect their reproductive parts, scientists believe.
A new study suggests the "high-energy honey" might not just be a "come-on" to bees and other insects to attract them to pollinate the flower but it might also be protecting other critical parts of the flower such as the stamen and stigma.
Scott Armbruster, professor of ecology and evolution at the University of Portsmouth, said: "Contrary to the accepted wisdom, the role of nectar seems in this instance to not be just about attracting and rewarding pollinating insects.
"It seems nectar and nectaries, the glands which produce it, attract herbivores that would otherwise feed on other flower parts. Thus the nectar and nectaries may be acting as a decoy.
"Like nectar thieves and robbers, the herbivores we observed have a high energy demand and, because nectar is rich in nutrients, it appears flowers are using it as a distraction, to keep herbivores away from critical reproducing parts of the flower, which are also edible.
"They are sacrificing their nectar and nectaries for the greater goal of maintaining other floral parts that are critical for attracting pollinators, and hence being pollinated."
Prof Armbruster worked with scientists from universities in Wuhan, China, Calgary, Canada, and the Fairylake Botanical Garden in Shenzen, China, to study the role of nectar for the research published in Biology Letters.
A University of Portsmouth spokeswoman said: "The researchers studied Iris bulleyana, with showy, large, colourful petals, which conventional wisdom says are a means of attracting the attention of bees and other pollinators.
"Nearly all (98%) of the flowers studied in natural conditions were damaged by herbivores, but in 85% of the flowers, damage was restricted to just the nectaries, suggesting nectar was being sacrificed to protect more critical parts of the plant.
"The researchers saw sawflies 'frequently' using the flower as a mating site during which all the nectar and nectaries were eaten, mainly by female sawflies, causing no damage to the stamen and stigma, the reproductively critical parts of the flower."
Prof Armbruster added: "The results are clear that floral tissues with a higher reproductive importance are essentially protected through the presence of sacrificial parts - the nectaries and nectar."