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| Wasp damage on Cosmos |
A neighbour of mine recently showed me some Cosmos stems
that had linear scars along them. When
she told me that it was wasps that had done the damage, I wasn’t particularly
surprised being familiar with their habit of chewing up any suitably soft or
weathered wood. I’ve often seen them on
fence posts where they chew little grooves along the grain of the wood. As far as I know, wasps are not into wood
carving or marquetry, so what is going on here?
The simple explanation is, of course, that they are making papier
maché. This is not the papier maché that
we made out of torn up newspaper and flour paste in school handicraft classes,
but a much finer version made out of wood pulp and wasp spit. Nor are they making model animals or lumpy
boxes, but rather the beautiful, intricate and delicate structure of their
nest, which includes both the many layered (and therefore insulated) outer
shell and the honeycombs inside where the wasp grubs will incubate.
I don’t know what attracts them to Cosmos in particular, but
I suspect that it not only provides the wood pulp for their nest, but also
because the sap is not far beneath the surface, it also satisfies their sweet
tooth. It is their sweet tooth that also
makes them such a nuisance at picnics, and it’s their nuisance value that makes
many people want to destroy their nests at every opportunity, whether they are
interfering with your gardening or not.
For good reasons why you shouldn’t do that, I can recommend an article written
by Steve Backshall in the Daily Mail on that very subject. And if you have an aversion to reading the
Daily Mail, then it is on-line at http://www.dailymail.co.uk/sciencetech/article-2748653/Why-learn-love-WASPS-They-ve-vanished-summer-But-s-shouldn-t-celebrate-writes-STEVE-BACKSHALL.html
(or better still just Google Steve Backshall Daily Mail Wasps.)
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| German Wasp chewing a garden chair |
I mentioned the honeycomb structure above, but it has
nothing to do with honey, as there is only one British native (introduced)
species that stores honey – the honey bee (Apis
mellifera). I was recently asked by
a friend how honey bees manage to build such a regular hexagonal
structure. I didn’t know, of course, but
I did vaguely remember some research published in the last year or so that
provided an explanation. I found the
article which was published as a news item in Nature magazine, as well as the
full text of the research paper. (See http://www.nature.com/news/how-honeycombs-can-build-themselves-1.13398
) Basically, what happens is that each
bee tries to build a circular cell of a particular diameter (6mm) as close as
possible to the next bee doing the same thing.
As the cell grows they turn into a series of adjacent cylinders which
are heated by the bodies of the wasps which partially melts the wax. This allows surface tension to pull the wax
into a basically hexagonal shape. (You
can show this by creating identically sized bubbles in soapy water, which then
form perfectly regular hexagon-shaped bubbles on the surface. The research team showed it by melting
bunches of plastic drinking straws.) The
bees also knead and reinforce the wax to make sure that the walls don’t get too
thin. The result is the perfect hexagon
pattern of the honeycomb which has rounded internal corners, no doubt for the
comfort of the grubs.
This does leave some questions unanswered though – like how
do the bees measure the circle in the first place? I suspect that this has to do with the fact
that all worker honey bees are roughly the same size and they will measure
things like we did before we invented rulers and inches. We had to use measures like cubits (the
length of your forearm) and spans (the width of your outstretched hand). It’s probably got something to do with the
size of the bees head.
The next question is – how do wasps make their hexagons with
papier maché which doesn’t melt like wax does?
Maybe it’s something to do with surface tension as the paper dries, but
the truth is – I haven’t a clue. It’s
still marvellous though.
