2019-11-23 New Scientist

(Chris Devlin) #1

54 | New Scientist | 23 November 2019


Nettle effect


How is it that stinging nettles don’t
seem to affect my dog’s sensitive
nose and ears or his relatively
fur-free belly while I respond rapidly
with a very painful skin rash?

Fiona Hussey
Aylesbury, Buckinghamshire, UK
Nettles are covered in tiny,
hair-like structures called
trichomes with fragile ends that
break off when touched. The ends
act like needles, injecting chemicals
that cause irritation and pain.
The outer layer of skin on a dog’s
nose is very thick, so I suspect that
the trichomes are too delicate to
penetrate it. The rest of the dog’s
body has hair, and even though
the ears and belly have much less
hair than elsewhere, it probably
still provides protection.

Pamela Manfield
Monmouth, UK
A friend recently told me that he
hasn’t felt nettle stings since a
boyhood experience. At the age
of 6, riding his new bicycle while
wearing shorts and a T-shirt,
he overbalanced into a patch
of nettles and was badly stung
all over his body. Since then, he
hasn’t had a problem with them.
Perhaps it is the same for dogs.

Dogs probably are shielded from
stings for the most part, but can feel
them. A recent article in Veterinary
Record Case Reports (DOI: 10.1136/
vetreccr-2018-000672) describes
two gun dogs that were treated
for suspected toxic effects from
sustained exposure to nettles – Ed

Hourglass figure


Why do wasps have such
a narrow waist? What could be
the advantage of having such
a narrow join between thorax
and abdomen, which seems
like a very weak point?

David Muir
Edinburgh, UK
Key to the evolution of certain
insects was a change from feeding

on plants to laying eggs on or
in the bodies of other arthropods.
The eggs hatch and the larvae
eat their host from the inside,
eventually killing them.
Around 250 million years ago,
at the start of the Triassic period,
a species of insect evolved to have
a narrow waist, called a petiole.
This adaptation allowed greater
flexibility and manoeuvrability
of the ovipositor, the tubular
structure on the female’s rear
used to deposit eggs.
This insect was the last common
ancestor of bees, wasps and ants.
In some families of Apocrita,
the wasp-waisted insects, the
ovipositor has morphed over
time into a stinger – as lots of us
have discovered to our cost.

Hazel Russman
London, UK
Wasps and bees have a narrow
section joining their thorax to
their abdomen, so they can curl
their abdomens under to sting
you while resting on your skin.

Dan O’Donovan,
Solihull, West Midlands, UK
The waist is narrow for flexibility.
This area needs to act like a hinge,
but unlike with a finger joint in
humans, it isn’t surrounded by
flexible skin and flesh. Instead,
it has a hard outer casing and a
thin membrane that can flex only
a little. If this hinge were thicker,
the membrane would have to
flex further and more quickly.
The joint is only as wide as
it needs to be for itself, nerves
and other plumbing.

Getting used to it


I grew up in Perth, Western
Australia, where summer days are
often in the high 30°Cs. I found this
warm, but not too hot. But after a
year living in the UK, I was wearing

shorts when it was just 21°C.
Obviously, I had acclimatised
to the local weather. Is this a
psychological or physiological
process? Do any changes occur
in the body?

Neil Holmes
Bromsgrove, Worcestershire, UK
Acclimatisation will be a factor,
but differences in relative
humidity of the air are probably
more important. In warm
weather, the cooling effect
of the evaporation of sweat from
the skin is vitally important.
When the air temperature in
Perth is in the high 30°Cs, the
relative humidity is usually very
low, often about 40 per cent or
lower. This allows sweat to readily
evaporate from the skin, keeping
the body comfortable.
The air in the UK in summer
is usually more humid. At 21°C
and a relative humidity of 70 per
cent, there will be less evaporation
of sweat from the skin and so
less heat loss. So the body will
feel comfortable at this lower
temperature.

Eddy Richards
Allanton, Scottish Borders, UK
When I moved to Kenya, I
experienced the same adaptation,
but in reverse. After a few months,
I started to put on a jumper when
the temperature dropped below
about 24°C. Returning to the
UK was a bit of a shock, because
it was snowing at the time,
but I rapidly reacclimatised.
However, even 30 years later,
I still find high temperatures
perfectly pleasant. This makes
me think that the effect is
psychological and is a reaction
to changes in the typical
temperature locally.  ❚

This week’s new questions


Time to think Are longer-lived animals such as turtles or
tortoises typically more intelligent than those with shorter
lifespans? Deborah Hartstein, Sydney, Australia

Mind fuel How many calories go on running the brain?
Could I burn more calories by trying to do lots of difficult
mental arithmetic or solving the New Scientist cryptic
crossword? Could I actually think myself thinner?
Thomas Reid, Dundee, UK

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