On Friday I received a phone call asking ‘are seagulls in Devon acting weirdly because of flying ants?’. The answer was very likely yes – flying ant day is a special day for gulls, and for many people the excited squawking of feasting gulls is the first sign of flying ant day.
The next question, however, was ‘could seagulls be made delirious by formic acid from the ants?’. Gulls have apparently been hit by cars because they are ‘stupefied’ and wandering onto roads.
The popular press are answering this second question in increasingly dramatic ways: gulls are made ‘yobbish’ by ants apparently! But the real answer has to be the scientist’s favourite of ‘maybe’.
I haven’t found any studies confirming that formic acid is causing the gulls’ behaviour, but we do know that Lasius niger (the black garden ant, responsible for most of the flying ant emergences we see) can produce formic acid.
Other possibilities include the heat, lack of awareness of the road because they are busy eating the ants, or just that gulls have become more noticeable. Delirious gulls are sometimes suffering from lead poisoning, or have botulism from drinking stagnant water, rotten food stuffs or maggots feeding on rotten things.
If we’re going to draw any conclusions about the effect of flying ants on gulls, we will have to study it in more detail. This could mean collecting more observations, finding out how much formic acid is in flying L. niger and seeing whether the ‘stupefied’ gulls recover when they cool down, or when they are no longer eating flying ants. It’s worth noting that some ant species produce more formic acid than others.
A relevant observation is that some birds are well known to use formic acid to kill parasites from ants, in a process called ‘anting’. They will sometimes eat the ants (and hence formic acid) at the same time, though anting perhaps also performs the role of reducing the formic acid birds ingest.
This discussion raised two interesting points which are central to lots of scientific investigations. Firstly ‘correlation does not mean causation’. It could just be chance that ‘delirious gulls’ are being sighted at the same time as flying ants, or it could be that the weather conditions chosen by the ants are causing this behaviour in the gulls.
The second is that absence of evidence does not mean evidence of absence. Just because I haven’t been able to find reliable evidence about the link between formic acid and the gull’s behaviour, it doesn’t mean that this isn’t happening. So, if you see gulls acting strangely, whether or not there are ants around, please add your information to the comments below!
I will also take this opportunity to explain why I dislike the word seagull. There are many different species of gull, from the bolshie great-black backed gull which loves to eat chicks, to the elegant ivory gull. They are all gulls, but not always found by the sea!