Why do bugs swarm over water? - Luke M. Jacobus
Like so many winged insects,
the world’s roughly 4,000 mayfly species
take to the skies
for their annual reproductive ritual.
These flights happen above every kind
of freshwater body on Earth,
barring Antarctica
and a few remote islands.
But whether the breeding mayflies
are large Hexagenia limbata,
tiny Paracloeodes minutus,
or the thousands of species in between,
their time on the wing will be brief.
Very brief.
For most mayflies,
adulthood lasts roughly one day.
And for some species,
it’s only a matter of minutes.
This isn’t because they’re all
eaten up by predators—
though they are a favorite food
of many fish, birds, and larger insects.
Rather, this abridged adulthood is
a natural part of their life cycle.
A close look at these insects reveals
they've ditched functional mouths
and digestive systems.
Without these innards taking up space,
mayfly bodies can store more eggs,
with some species producing
up to 12,000 per individual.
This adaptation is essential
to mayfly survival
since relatively few of these unborn flies
are likely to reach adulthood,
and even fewer will successfully
reproduce themselves.
In most of these flights,
male mayflies form dancing swarms,
which female mayflies move
through until a male grasps them
for some mid-air mating.
Some all-female populations can
reproduce without joining in the dance,
using a process called parthenogenesis
to produce viable offspring
without the help of a male.
And recent research suggests some mayfly
populations may even switch back and forth
between these two forms of reproduction.
But regardless of how the eggs
are made ready,
the female will deposit them
on or under the water,
and promptly perish.
This might sound like a tragically
brief existence.
And even mayflies’ scientific name,
Ephemeroptera, refers to their
stunningly short lifespan.
But for centuries, fishermen suspected
that mayflies live much longer
than this short flight.
And in 1681, scientists finally caught
up to their fishing friends
with a published account
of the full mayfly life cycle.
When the time is right,
these eggs will hatch.
Depending on the kind of mayfly,
this can happen as late as several months
after the egg is laid,
or even before it’s completely left
the mother’s body.
But whenever their egg opens up,
the mayfly inside quickly finds
its way into fresh water,
and it’s in this aquatic, nymph stage
that mayflies spend
the majority of their lives.
Inhabiting rivers, small streams,
ponds, lakes,
and other places with clean fresh water,
most mayfly species stay in this
nymph stage and feed underwater
for nearly an entire year.
In fact, some species live as nymphs
for up to two years
before they metamorphose
into their winged adult state.
A year is a long time for such
a small creature to stay alive.
So to survive and thrive, mayfly species
have a wide variety of habits
and corresponding body forms.
Sprawlers are flat enough to stick
to surfaces
despite the strength of a current,
while clingers accomplish the same feat
with suckers and claws.
Other species are swimmers,
crawlers, or borers.
One of the most noticeable groups
are the burrowing mayflies;
sizable specimens which use
their legs, tusks,
and a scoop on their heads
to dig U-shaped tunnels.
In these muddy dwellings,
the nymphs use their abdominal gills
to accelerate water through their burrow,
filtering it for food along the way.
After they metamorphose,
adult swarms can get so large
they appear on weather radars like rain.
Regardless of how they've adapted,
each unique species plays
an essential role in their ecosystem.
Plus, nearly all mayflies are a staple
of freshwater fish diets,
and since they ingest the smallest
particulate matter in their environment,
mayflies are also very sensitive
to water pollution.
In fact, scientists can tell a lot
about a water body’s health
based on which mayfly species they find.
If they don't find mayflies at all,
it's usually an indication
that something is wrong.
So the next time you see a swarm
of mayflies over a pond, bridge,
or park fountain,
remember that their short aerial dance
means a healthy world exists
below the surface.
