Sep 10

Why are moths attracted to flames? (and other mini questions)

The natural world is full of small niggling questions. How do fish in the ocean drink? Why are zebras black and white? What came first, the chicken or the egg? We occasionally ponder these queries but then we quickly move on, perhaps thinking the answer will be either too complicated or too mundane. As it turns out, this is very rarely the case.

Why do pigeons bob their heads?

We see pigeons virtually every day of our lives, either walking past them on our way to work or almost running them over in our cars because they refuse to fly out of the road until the very last second. They strut around the streets, bobbing their heads frantically – and yet we never ask why. Do they enjoy it? Are their legs somehow attached to their heads?


Photo: Ken Simonite

It’s all to do with their eyes. Though they are remarkable in theory – the top half of the eye sees at great distance; the bottom half sees detail close up – they cannot move in their sockets. They are also on the side of the pigeon’s head so they don’t have the benefit of stereo vision (depth perception), and this means the world probably looks quite flat to them. But by bobbing their heads to-and-fro, pigeons are able to compensate for this by observing the world from slightly different positions, helping with depth perception.

Why are moths attracted to flames?

The short answer is that they are not – they are actually disorientated by them. Ever since moths evolved to be nocturnal animals, they have used the only light sources available to them, namely the sun and the moon, to navigate. They expect (if an insect with a near-microscopic brain can expect anything) the light from those sources to strike their eyes in the same place at different times of the day or night, enabling them to calculate how to fly in a straight line.

But then humans came along and invented fire and, much later, the light bulb. The moths became extremely confused when flying past these artificial light sources. If you think about it, a moth never actually ‘expects’ to reach the moon, or to be able to fly above it, so if it gets close to an artificial ‘moon’, its orientation is greatly thrown off.


Photo: Dr John Brackenbury

The insects assume they are flying in a curved path because their position, in relation to what it ‘thinks’ is a stationary and faraway moon, has now changed, and so it must adjust its course until it sees the light as stationary again. With the light source so close, though, the only way this is possible is to fly around and around the light-emitting object in ever-decreasing circles, sometimes to the point that they touch it and are killed.

Can an insect survive without its head?

Yes – and for quite a while. Unlike higher organisms, such as vertebrates, which have a massively important centralised brain located in their heads, invertebrates like insects have a nervous system based instead on ganglia – small nerve nodules – that are repeated in each body segment. The ‘brain’ ganglion is the most important but it is not the vital, all-powerful, overriding organ that we associate with vertebrate anatomy.

If an insect is decapitated for whatever reason, and if we assume it doesn’t lose a lethal amount of haemolymph (insect blood), then it can quite happily carry on with its life for hours or even days as a kind of automaton. There won’t even be much change to its body function, breathing or behaviour. The major problem is that without a head an insect cannot feed and so it will eventually starve to death.

What came first, the chicken or the egg?

The egg, every single time. Before the chicken, there was a chicken-like bird that laid eggs, and before that another egg-laying bird. The first ever bird must also have come from an egg, for we now know that birds evolved from reptiles – in particular, small, bipedal carnivorous dinosaurs (think the ‘Compys’ from the second Jurassic Park movie if you will).


Photo: Dennis Novak

Even if we go further back in time, the amphibians that evolved into reptiles laid eggs, and so did the fish that would later evolve into the first amphibians. In fact, since every multicellular animal produces eggs, even if they are just tiny cells within the body, then the first true animal, which probably lived around a billion years ago, almost certainly produced eggs too. I think we can finally lay this one to rest.


2 pings

    • Alex S. on September 19, 2013 at 11:44 am
    • Reply

    I’ve been wondering this for a long time: if mammals are the only animals to produce milk, how can pigeons produce it to feed their young as well?

    1. Good question, I’ll include that as one of the questions when I do a follow-up to this post.

  1. […] September, I published a post entitled ‘Why are moths attracted to flames? (and other mini questions)’, which aimed to answer questions about the natural world that were neither large nor detailed […]

  2. […] the third Mini Questions entry (see here and here for the two previous ones), Extraordinary Animals will once again be probing into a few […]

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