Saturday, 16 July 2011

Birds and ant swarms

In July and August, typically in sunny days after rains, swarms of reproductive Black Garden Ants (Lasius niger) - winged queens and males - emerge from their nest to mate and start new colonies. Workers also come out en masse and run around the entrance of the nest, looking agitated. I had often noticed this and wondered why do workers did this, until yesterday, watching a Blackbird feeding on the winged ants coming out of their nests, realised why. The Blackbird run close to the entrance, fetched a winged ant and run away. The bird repeated this several times and was obviously being stung or sprayed by the ants around the nest, but still wanted to feed and its back-and-fro behaviour was evidence of the - at least partial - success of the frantic workers keeping predators at bay. Winged ant have many predators. Some casually feeding on the winged ones, others opportunistically making use of a plentiful, although ephemeral, bonanza. A range of birds fall in the latter category, starlings and sparrows feed on the winged ants - sometimes using fly-catcher techniques - and seagulls have been seen feeding on them up in the sky. While reading a paper on this, I remembered that last year, on the day the ants emerged, I looked up in the sky and saw many small flying things and thought they might be the flying ants. When I looked more closely I saw they were seagulls, and was surprised at how many there were, well over a hundred, soaring very high up. I took a shot (below) and forgot about it. They were most likely feeding on the winged ants that had been carried high by thermals in their swarming mating flight.
Seagull flock feeding on swarming ants (26/07/10)
This is the nest in the bottom right hand corner of the top photo
Workers around a nest with winged ants emerging (26/07/10)

Reference
James Baird and Andrew J. Meyerriecks (1965). Birds Feeding on an Ant Mating Swarm. The Wilson Bulletin, 77 (1), 89-91.
Gilbert S. Grant (1992) Opportunistic Foraging on Swarming Ants by Gulls, Shorebirds, and Grackles. The Chat, 56, 80-82.

3 comments:

Julian & Fiona said...

Hello Blackbird,
Just found your blog after googling 'trigger for swarming in lasius niger' ... every year one of our barn walls is covered in winged ants for a day. It happened yesterday on a muggy day. Thousands of ants, but after reading your blog, and your description, I wonder if they always swarm onto this wall, because the nests are at the base of this wall, which faces South East. I couldn't see any wingless ants, around though.....perhaps too many winged ones for me to spot them. Any ideas if this number will be from just one nest, or perhaps several....it could be there's a special microclimate at the base of this stone wall. Very interesting blog anyway,
thegardenimpressionists

thesciencesays said...

I just read your blog because I'm about to blog for http://soicetyofbiologyblog.org on exactly the same topic. I thought you might like to know about a survey we have launched this year asking for records of flying ants:

http://www.societyofbiology.org/newsandevents/biologyweek/flyingantsurvey

Africa Gómez said...

Thank you for your comment thesciencesays. Very interesting project, I will indeed log my flying ant records from the last few years.