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Butterflies are beautiful and never sport absolutely horrifying tentacles.
This is well known.
Or is it?
Everyone likes butterflies, right?
That’s not true, ​​lepidopterophobia is a real thing and, like, why not.
Cockroaches are awful and everyone hates them,
and though they certainly seem less magical
than a monarch gliding gracefully on a massive migration,
cockroaches and butterflies are both just bugs.
Still, most of us like butterflies because they look nice,
and that might actually end up being good for them because it makes us humans,
who have a pretty large amount of control over this planet,
more likely to protect them.
But that is not why butterflies are pretty.
They are able to use the colors of their wings for camouflage,
to scare predators, to warn (or bluff) that they’re poisonous.
There’s also pretty good evidence that, in at least one species,
female butterflies prefer more brightly colored males.
That might be because it indicates that they’re better mates
and would have caterpillar babies with a better shot at butterfly lives.
And so, in those cases, what a female butterfly finds attractive
also just happens to be what we find attractive.
Unless we’re talking about coremata!
Butterflies have some pretty intricate systems for mate selection,
and for them, pheromones play a major role.
Pheromones are chemicals produced by one animal that
affect the behavior of another animal, and are often carried through the air.
Butterflies use them for courtship.
Often, a male will use pheromones to attract females to them,
and the airborne chemical signals are also
thought to make females more receptive to male advances.
This is not a thing that we tend to notice about them,
but it is a very big deal for the lepidopterans.
That’s the umbrella term for butterflies and moths,
not the name for aliens from the planet Lepidop.
And so some groups of butterflies and moths have special organs
for spreading their pheromones more effectively.
These include little patches of specialized wing scales that you would never notice.
And they also include coremata:
inflatable hairy tentacles that shoot out of their butts.
The butterfly lobby has clearly been trying to hide this from us.
When a male of one of these species wants to attract a female,
the insect inflates large organs from the rear of their abdomen that
increase the surface area from which the pheromones can evaporate.
The inflating happens either with air or with hemolymph, aka insect blood.
And this, basically, allows the insects to be stinkier.
Sometimes coremata are small and not too terrible,
but in some moths they can be absolutely massive.
Like, up to 37 millimeters in one species; as long as their whole wingspan.
This particular species of tiger moth has four of these structures
that it can retract entirely back into its body.
But, when it needs to really waft its scent out there
in the hopes of attracting a mate, it inflates these organs.
Clearly there is some significant evolutionary pressure
to really get that smell going.
This is likely because some species with coremata use a reproductive strategy
called lekking in which males all gather together to display to females.
In general, a lek refers to a gathering of males,
who might display with loud sounds, bright tail feathers or,
in the case of some Lepidoptera, extravagantly wafted scents.
Indeed, another species with impressive butts
that form leks is more familiar: peacocks.
Males who impress females are then selected for mating.
That creates strong evolutionary pressure for whatever trait is being selected for.
In some moths from the Erebidae family, including our tiger moths,
it seems that trait is giant butt tentacles.
In fact, this is a well-known problem in evolutionary biology called the Lek Paradox.
If females are exclusively selecting males for this trait,
then it should cause a runaway lack of diversity, with only males with the
absolute best wafting organs getting to spread their genes.
That lack of diversity would then be bad for the survival of the entire species.
But, for some reason, this doesn’t seem to happen with lekking species.
And there are a few hypotheses why.
One idea is that even though the selected traits do hold the species back,
the males in question are so fit that they still make worthwhile mates.
But a more prevalent hypothesis is that
somehow the selected trait is itself a sign of fitness.
Like, maybe a moth doesn’t grow big coremata because
it has the right genes to grow big coremata.
Rather, it has to be a successful individual or else the coremata won’t get so big.
That means that females aren’t selecting for
specific genes that lead to big coremata.
They’re selecting for overall healthy individuals
and genetic diversity doesn’t take so much of a hit.
For some Erebidae moths, this appears to be exactly what is happening!
The size and full development of their coremata is directly influenced by how much
of a specific chemical they’re able to ingest while munching around as caterpillars.
Adult males who ate well as caterpillars have the biggest coremata and
the strongest pheromones, and they gather in leks to
signal to females that it’s time to mate.
Unlucky males with smaller coremata don’t even try to join in:
they wait until the females that haven’t mated yet start signalling
later in the day and join in mating that way.
We have no idea why these species started doing this, though,
so the lek paradox remains a mystery.
Anyway! It’s important to note… not all butterflies and moths have coremata,
and most are much more modest affairs than these tiger moths.
But this is a reminder that butterflies and moths are not here to please us.
Their beauty is an accident, as is their occasional horror.
We are merely spectators.
And one of the coolest things to observe about butterflies is their ability to
detect Earth’s magnetic field.
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because we have Brilliant.
Brilliant is an online learning platform that offers guided problem-solving
based courses in math and science, like their science course
on electricity and magnetism.
That’s a topic that is way more interesting with interactive examples than it
would be to read about in a textbook.
So Brilliant provides everything from diagrams to quizzes to keep you engaged.
Click the link in the description down below or visit Brilliant.org/SciShow and
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