Hey everyone, it's Inés and welcome back to Draw Curiosity!
As you probably all know by now, I've spent the past few years completing my thesis in
insect flight, and thus far the two prime uses of my ultra narrow expertise go towards
this… [choosing doctor on sign up form] and regaling anyone who cares to listen with
niche facts about insect flight.
So trust me, the latter is way more fun so without further ado, here are 5 of my favourite
facts about insect wings that you may not know about!
[Intro by Caro Waro & Cristina de Manuel ]
Number one - Sexual dimorphism!
In biology, sexual dimorphism is where the two sexes within a species display different
characteristics beyond their sexual organs.
For instance, in many species, females are much larger than the males, and in many bird
species, the males are much more colourful and ornamented compared to their female counterparts.
These differences also extend to the wings of many insect species, as the male sex of
several species use their wings to serenade and attract the females.
For example, male fruit flies extend their wings and they vibrate them to generate a
courtship song to increase the female’s receptivity.
However, my favourite example of sexual and natural selection in action comes from the
oceanic field cricket, Teleogryllus oceanicus.
As you know, male crickets rub their wings together to generate the infamous cricket
sound to attract the females.
Now whilst the wings in male and female Drosophila are mainly different in size and possibly
aspect ratio, in crickets their structure is completely different: the males use the
plectrum on their left wing, which has lots of minuscule teeth, to rub against the file
of their right wing, which is the hardened Cu2 wing vein, to generate their characteristic
sound.
They additionally have structures known as the “harp” and the “mirror”, which
are resonators.
However, when you’re a noisy male cricket, you don’t only draw the curiosity of female
crickets, but also the attention of predators and, in the case of the oceanic field cricket,
of parasites.
There is a parasitoid fly, Ormia ochracea, which uses the cricket’s song to locate
the crickets and flick their eggs onto them.
The larvae then burrow into the crickets, eventually killing them a week later when
they emerge.
How wonderful!
And this has led to the evolution of a new form of male which is completely silent and
it has a wing that more closely resembles that of a female.
Of course, this protects them from the parasitoid fly, as they can no longer be traced, but
you might also be wondering how they attract the females instead.
And the answer is they still rely on the singing males - which they too track down by listening
out for them, but then they simply intercept any females passing by, before they find the
singing male.
Isn’t nature wonderful and sneaky?
Number two - the pterostigma!
The pterostigma is a small pigmented spot found close to the leading edge on the outer
edge of the wing in some insect orders, such as Odonata, which are the dragonflies, Neuropterans,
such as lacewings, Psocoptera, the barkflies, Hemipterans, which are true bugs, and Hymenopterans,
the bees, wasps and ants.
Even though at first glance it may seem insignificant, from an aerodynamic perspective the spot makes
quite a substantial difference.
The pterostigma is essentially a thicker sclerotised mass, which makes it relatively heavier than
the surrounding bits of wing.
Throughout the length of an insect wing, the torsion axis of the wing, which is the axis
around which the wing twists length-wise, lies ahead of the chord-wise centre of mass,
with the exception of the pterostigma, which brings the centre of mass closer to the wing
tip.
And the reason for this is that in gliding flight, where the wings aren’t necessarily
flapping, if the centre of mass is too far behind the torsion axis, wing flutter can
occur at sufficiently high speeds.
Flutter is quite a serious aeroelastic phenomenon - it’s the phenomenon that took down the
Tacoma Narrows Bridge in 1940, and is also very dangerous when it occurs in aircrafts.
It is a self-excited oscillation of the structure of the aircraft, or in the case of the insects,
of their wings, where the energy from the airstream is absorbed into the structure.
At flight speeds beneath flutter speed, the oscillatory motions decay and they don’t
cause any further damage, but when the flutter speed is reached or even surpassed, the oscillations
can increase in amplitude and lead to massive structural failure.
So as a result, aircrafts are rigorously tested for flutter, and their structures are reinforced
to protect them from reaching dangerous warping at the high speeds.
That being said, I will say don’t worry if you look out of an aircraft window and
you see some wing bending, that is perfectly fine and normal, this is nothing like the
levels of flutter that we are talking about here.
And in the case of dragonflies, the pterostigma takes up only 0.1% of their mass, but enables
them to increase their maximum gliding speed up to 10-25% depending on the species, which
demonstrates how a little bit of optimal engineering can make a huge difference to flight performance.
Number 3 - the alula The alula is a hinged flap found in the wing
of Brachyceran flies.
Brachyceran flies include flies such as hoverflies, house flies, fruit flies, blow flies… but
not flies such as mosquitoes and crane flies.
The alula is controlled by one of the flight muscles, and although its effect is variable
it significantly changes the effect of the wing beat trajectory in flight, providing
these flies with another way of altering their position and speed when they fly.
Also fun fact, this is actually the work of one of my supervisors!
Number 4 - wing folding!
Not all wings are created equally.
You may have already noticed in the wings we’ve seen so far that they have a plethora
of neat features which allow the insects to change the shape of the wing depending on
their circumstances.
One of my favourite extreme examples of wing deformation are insects who fold up their
wings.
For instance, beetles only have a single pair of wings.
Their front pair have hardened and been modified through evolution into elytra, and they actually
serve to protect the hindwings which are folded up inside when they’re not flying.
Apart from their nifty folding mechanism, ladybirds can deploy their wings in a tenth
of a second, which is actually faster than the blink of an eye (150-400ms), and that
enables them to take flight quickly if endangered by any predators.
But also, the process of folding them back up again, although it is considerably slower,
is still relatively speedy.
Rove beetles take it to the next level, as their elytra are shortened, and their wings
fold asymetrically, meaning that their folding mechanism to package them away is even more
sophisticated.
Earwigs, however, I think take the prize, they are the most impressive of the lot: depending
on the species, their wings when unfurled can be 10 to 18 times greater in surface area
than when tucked away, and they can unfurl them with no muscle activation whatsoever.
They achieve this with many resilin junctions present on their wings.
Resilin is a rubber-like protein present in wing vein junctions and the joints in many
insects that is extremely efficient at storing elastic energy.
In dragonflies and bees, it aids with wing torsion during flight, but it also plays a
crucial role in insects that engage in wing folding by allowing the wing to ‘spring-load’
and snap into different configurations when folded and unfolded.
Understanding how insect wings fold and the properties of the materials in the wings actually
has implications for the development of foldable electronics, such as storing and unfolding
solar sails for satellites and space probes, or designing products such as compact tents.
Number 5 - hairy wings!
Last but definitely not least, insect wings are actually quite close to me when you look
at them up close - they're kind of hairy! and all of their hairs naturally have different
functions.
There are macrotrichia, which are large socketed hairs generally found on the wing veins.
In the case of Lepidopterans, which are butterflies and moths, and Trichopterans, which are the
caddisflies, the macrotrichia are highly modified to be the colourful scales that cover their
wings.
There are also microtrichia, which are smaller and more irregularly scattered, and are thought
to have a variety of functions.
One of the main ones is they are thought to protect the wings from drops of moisture.
The spacing and the direction of the microtrichia on the wings make them almost impermeable
by drops of water, which land and are quickly guided off and away from the insect’s body.
The distribution of microtrichia also varies immensely across different species, and in
species of beetle they are also known to play a role in helping to hold the wings that are
being folded in place underneath the elytras.
And finally, I want to give a special shoutout to the Hymenopterans, which comprise the bees,
the wasps and the ants, as they have quite a few more hairy wing features.
Firstly, most if not all of the winged Hymenopterans have a row of hooked hairs, also known as
“distal hamuli”, which are found on the leading edge of the hindwings and they serve
to hook them onto the forewing during flight.
This means that despite having two pairs of wings, they function as a single pair during
flight.
And secondly, there is also a highly diverse group of parasitoid wasps which are actually
so minute that their wings, rather than being disk shaped are more comb or brush shaped
- they are formed by a very tiny disc and several setae.
The reason for this is that at that size, the air is so relatively viscous that despite
the hairs being separate, the air does not pass between the hairs.
So there you have it - 5 insect wing facts that hopefully you didn't know about!
By the way, whilst this video is not sponsored - I do have a little announcement to make!
You may have noticed that 14 edutubers and I from the “Smart YouTuber Mafia”, AKA,
educational youtubers you may already be watching, and if you aren’t, probably should be watching
because you'd probably really like them, have been collaborating on a thoughtful subscription
box called “The Singularity” - and the first edition is going to be shipping out
in mid-April - I believe the 22nd!
It contains a plethora of items and merch, I'm going to say easily my favourite is a
CGP Grey's Bonnie the Bee plushie, after all of this insect talk you probably know why,
there's also an environmentally friendly water bottle from MinutePhysics, there are actually
a ton of different things aaaalso some postcards contributed by yours truly which I photographed
and illustrated myself!
So - if this sounds like something you would be interested in, you can check it out on
the website.
If you use the code 'drawcuriosity', you will also get $5 off.
This is a physical product, so it's shipping from the US - if you're within the US shipping
is free.
If you are ordering from the outside, please check your customs regulations in your country
- I don't want any nasty surprises.
I've heard there might be an EU fulfilment centre in the future, but that's not the case
right now.
So if a thoughtful Singularity is something that sounds like something you want, then
feel free to order before mid April, cos if not that's apparently it until June when the
next edition comes out, and if it's not, that's totally fine as well!
As always, thank you so much to my incredible patreons on patron for supporting the creation
of this content, and as always, thank you so much for watching and I’ll see you in
the next one!
[Music: Intro - Johnson by Thastor, BG music - CryoSleepKitten]
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