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| How fish school |
During last week’s
snorkel around this beautiful little lagoon did you happen to notice all the
little fish swimming around near the surface? Ever wondered how they all manage
to change direction at the same time? Yes, you can put your towel down and
sunbathe now but just take a closer look at this couple of little fellows I’ve
just netted. Pretty aren’t they? That dark line going from stem to stern is
called the lateral line and it’s packed full of hair cells which can detect
minute movements and vibrations in the water. These signals are then sent
electronically to the brain giving the fish an extremely accurate picture of
its environment even in dark and cloudy waters. They can locate prey, avoid
predators and, of course, all turn together in a way that would make any synchronised
swimming team give up and take an early shower.
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| Cardinal Butterfly |
This is
just one of the methods that animals and plants use to communicate with each
other and while we’re sitting here enjoying the sun I thought we’d look at some
of the other ways they do it. That stunning Cardinal Butterfly that’s just
landed behind us for example. Easily recognisable by the way, from the greenish
sheen to its hairs. Bright coloured
butterflies semaphore their colours to each other and even the comparatively
plain female Cabbage White gives a brief flash of ultraviolet light on each
downstroke of her wings when she’s ready for a mate. So, butterflies too have
their flashers, not just the girls after a night out in the bars of Malia.
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| Blackbird |
Birds, as
we know, sing beautiful songs, particularly the males when they want to attract
a mate but even that is not as simple as it seems. During the reproductive
season the blackbird, famous for his ability to improvise and embellish his
repertoire, actually sings a simplified, functional version of his song
proclaiming ‘here I am’, ‘this is my territory’ ‘ready when you are’. All those
twiddly bits and sound incorporations (I knew one once who managed to include a
police siren into his song) come later when he has time to relax and
experiment.
Now, if
you could just move your towel a bit – no, it’s not in my way as such, it’s
just that you’ve parked it on an ants’ nest that I wanted to talk about. You
didn’t need to move it that far away – or quite so quickly. You’ve disturbed
the ants now but still, you’ve created masses of communication in the nest.
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| Ants have a sophisticated communications network |
Ants are what are known as eusocial insects (which is like social but to a very
high degree), living and working almost like a single entity. To get this level
of coordination you need a pretty sophisticated communications network and the
key to this is pheromones, chemical substances that can be detected by other
ants through various sense organs such as their antennae. Female moths use pheromones as well to attract
males over long distances and so do we to a certain extent (ever wondered why
you were inexplicably attracted to someone? Pheromones at work). But back to
theses ants; as well as chemoreception (the technical term for communicating
with pheromones) they are very touchy-feely creatures, passing information by
stroking each other with their legs and antennae and they are also surprisingly
vocal. We can’t hear them of course but they stridulate like crickets – that
is, they rub parts of their bodies together, and produce high pitched chirps.
Tree dwelling ants go one better, they also send vibration messages back to the
nest by drumming their heads against the wood (the insect world not only has
flashers but head bangers as well so when we say that certain disruptive
elements in our society are “behaving like animals” maybe we should be more
specific and say “behaving like insects.”). So what looks like a mass of
confusion down there is a highly complex hub of smells, vibrations and sounds
ensuring that every ant knows what it should be doing, and where and when it
should be doing it. Amazing little animals, ants. Have you got them all off of
your towel yet?
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| Mallow |
But what
about plants? The idea of plant communication was ridiculed for years (as in
the old song parody: “I talk to the trees, [that’s why they put me away]”) but
we are now investigating myriad ways in which plants pass messages to each
other. I spotted a little drama unfolding amongst the mallows on our way down
here so if you pack up your towel and sun-tan lotion I’ll show you on our way
back.
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| Ant and Aphids ona Mallow leaf |
Down here
on the leaves we have some newly emerged green aphids and an ant. The aphids
want to eat the plant and as they do so they will excrete a sugar rich
substance called honeydew. This is what the ant is after. The plant doesn’t
want to be eaten so it will mount a chemical defence and produce toxins to
deter the aphids. It doesn’t necessarily stop there as we now know that some
(maybe all) plants produce pheromones which shout the equivalent of “APHIDS - INCOMING!” to their neighbours who can then mount their own
defences prior to an attack. The question that arises in my mind is – how does
the ant just happen to be there as the aphids emerge? Could be he just stumbled
across them but we know that the ants’ main method of communication is based
upon pheromone chemoreception so, has the ant picked up the “APHIDS -
INCOMING!” transmission? Military intelligence in action as it were. This would
be counter productive to the Mallow as the ants will shepherd and protect the
aphids from predators such as ladybirds. It’s possible that the plants are
aware of the ants’ abilities and send out a scrambled pheromone message that
the ants can’t decipher and this one did indeed just get lucky. Or maybe the
ant has learnt to decipher the code? As always when we start looking at nature
in action there are far more questions than answers.
Until
next week – happy hunting and, as Sherlock Holmes would say: the trick is not
just to look but to observe.
Add your own comments and
observations by using the comments button at the foot of the page or find out
more about Crete nature by following the links below.
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LINKS:
Naturalists
(the facebook page that accompanies this blog)
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