Why ladybirds cluster together in winter
If you follow Sudbury Commons Lands on Instagram, (and if you don’t, why not give it go?) you will have noticed we have upped our game recently. We have redoubled our efforts to keep the feed alive with frequent images from the meadows and surrounding area.
Looking back over the past few months, the montage of nature photography tells a story of the changing seasons and the beauty that exists on our doorstep. In particular, the scenes of the frozen mill pond and icy dykes from the cold snap just before Christmas threw up some stunning imagery.
One picture especially caught my attention. It featured hundreds of 16-spot ladybirds clustered together on a fence post in sub-zero temperatures. It was an image that started me thinking. Ladybirds are among our favourite insects – their colourful, attractive armour and the fact they help to keep greenfly numbers under control means they are looked on kindly, especially by gardeners.
According to the hugely informative book Bugs Britannia by Peter Marren and Richard Mabey, our fondness for ladybirds goes deeper than this – the name originating from the Middle Ages and the cult of the Virgin Mary who was sometimes depicted wearing red. They were regarded as winged messengers from Heaven, more a bird than a mere insect – put the two together and thus the name ladybird.
An old Suffolk name for a ladybird is golden beetle while a collective term for ladybirds is a ‘loveliness’. It has long been considered bad luck to kill or harm one. The ladybird’s reputation for goodliness even goes as far as the publishing world where their name has been given to a much-loved series of illustrated children’s books.
But I associate these coccinellid beetles with the warmer weather of spring and summer, not an uber-chilly December.
From my reading I was surprised to find overwintering ladybirds are often found in clusters, known technically as aggregations. Some varieties prefer the nooks and crannies of stonework walls, others, such as the 16-spot variety, may be found in exposed positions, on trunks, posts, gorse, and plant stems. The largest recorded aggregation for this species is more than 10,000 individuals.
As the cold weather arrives, ladybirds group together in a state of diapause, a condition similar to hibernation where they shut down their bodily functions to brave out the cold temperatures.
Aggregations offer a number of advantages to aid survival. Grouped like this they create a warm microclimate within the huddle, which shields them from the harsh conditions they are likely to face during the winter months.
A mass of ladybirds also offers more protection against predators, such as birds and spiders because in a group there is less chance of being picked off than if they are solitary. There is also a theory that a large number of bugs altogether also intensifies their aposematic signals. These are the bright colours and markings – used by many creatures from moths to tree frogs – that warn off predators and tell them they are toxic and not nice to eat.
And predators should take heed of these warning signs on ladybirds because they are not given without good cause. When attacked, some ladybirds secrete a bitter tasting alkaloid fluid from their leg joints in a defence mechanism known as reflex bleeding. I certainly remember seeing this unpleasant yellow liquid on my hands as a child after I had picked up a ladybird. The fluid also contains a distinctive smell of a chemical known as pyrazine which lets the attacker know that the beetle will taste bad if eaten.
Experts also believe that another reason ladybirds cluster together over winter is that these groupings aid reproduction. Researchers have found that when the ladybirds start to rouse in spring, mass mating occurs among the bugs who find themselves in close vicinity to each other. Now, that is what you call a rude awakening!!!!
Ross Bentley, Trustee of the Sudbury Common Lands Charity