Even bees feel the blues when life gets them down in the mouthparts, scientists have discovered.
A study suggests the insects can display negative emotions just like humans, dogs, rats and birds.
Scientists upset a group of bees by shaking them violently to simulate an attack on the hive by a predator.
Later, the way they responded to odours indicated a pessimistic outlook.
They were less likely than undisturbed bees to extend their mouthparts to an odour predicting the bitter taste of quinine.
Novel odours produced the same reaction.
Researcher Geraldine Wright, from the University of Newcastle, said: “We have shown that the emotional responses of bees to an aversive event are more similar to those of humans than previously thought.
“Bees stressed by a simulated predator attack exhibit pessimism mirroring that seen in depressed and anxious people.”
The scientists, whose findings are reported in the journal Current Biology, first trained bees to link one odour to a sugary sweet reward and another to bitter quin-ine.
The bees learned the difference between the two and became more likely to extend their mouthparts to the “sugar” odour.
Next, one group of bees was shaken up while another was left undisturbed.
The bees were then presented with the odours again, as well as similar new odours. Agitated bees became even more averse to the odour predicting quinine, and were also put off by the new smells. They behaved as if they had an increased expectation of a bitter taste.
“What we have shown is that when a honeybee is subjected to a manipulation of its state that in humans would induce a feeling of anxiety, the bees show a similar suite of changes in physiology, cognition and behaviour to those we would measure in an anxious human,” said Dr Wright.
“In terms of what we are able to measure, a shaken honeybee is no less ‘anxious’ than a lonely dog or a rat in a barren cage.”
The scientists believe feeling blue is not unique to bees, and other invertebrates probably behave the same way.