Migration Theory PT2
Wednesday, June 29th, 2022 12:08 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
snoozefestaudioSo the other day I was speculating that crickets migrate into the southern hemisphere between October and March, then into the northern hemisphere between April and September.
But that would be an oversimplification of such a migration theory.
My focus would be on North and South America. But before we look at that, we should note that crickets exist on every continent but Antarctica.
The family Gryllidae, the crickets, in the order Orthoptera, evolved between 200 and 250 million years ago... on the supercontinent of Pangea. So they were well established everywhere before the contintents moved to their current global positions.
If we assume that crickets thrive year round within ten degrees north and south of the eqator, then in the Americas... that's most of the Amazon rainforest.
Across the Atlantic, that's the middle third of the African continent... that's the Congo.
Even further east, that's the islands of Malaysia, Indonesia, New Guinea, etc... between China and Australia.
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So my annual crickets, here in Illinois, are, according to the migration theory, coming from the Amazon!
There, between 10N lat & 10S lat, they live year round. But they're never ONLY in that band.
If we start at the March 20th Equinox... start of spring for the northern hemisphere, and start of fall for the southern hemisphere...
Then their population extends as far south as Argentina, way down in southern South America.
They are beginning to die off in Argentina, because it's getting a bit chilly. But at the same time, their population is beginning to spread northward out of the Amazon, up into Central America... Panama, Costa Rica, Nicaragua.
As we move through April and May, their numbers are dwindling fast in South America, but now they're expanding through Mexico, up into the United States.
And so it goes until the September 21st Equinox... start of northern hemisphere fall, and southern hemisphere spring.
By September 21st, they may not exist much further south than the Amazon, but their population extends north up into Canada, and the southern coasts of Alaska.
------------{=0=}------------
So, crickets are always alive and well, in about a 120 degree swath, north and south... which is huge! One degree of latitude is 69 Miles, so that's 8,280 Miles, or 13,325 Kilometers.
It's just that the 8200M N/S swath drifts north and south of the equator over time. In March, it's mostly in the southern hemisphere, in September, it's mostly in the northern hemisphere.
The crickets of the Amazon, ten degrees north and south of the Equator, are the only ones that never die out. In the areas outside of that band, they arrive and stay, until it's too cold and then they die.
The eggs stop hatching under 65F. But the adults can stay active down to 45F. Once it drops below 35F for a few days in a row... that's it!
Migration theory says the area's been sterilized completely, and won't be repopulated until new crickets from the Amazon make their way back... by hopping!
------------{=0=}------------
Now, even the above description is simplified. Crickets probably do exist year round at a little more than 10 degrees north and south of the Equator, especially in coastal areas that stay warmer longer.
And the speed of their migratory spread would depend on geography. So, for example, they make it up through Central America pretty quickly, because it's a narrow corridor. Wheras, once they get north out of Mexico, there's the whole huge expanse of North America to fill in, east and west.
That's, I assume, why they can make it up to, say Texas, a month after the equinox (April 20th) but it takes another three months to get up into Chicagoland in August!
------------{=0=}------------
Or at least I think it takes until August!..
Since I will be sooo bored this July... thanks to no wind for wind chimes, and living in the hole where no storms come through... I guess I'll just take notes as to exactly how the crickets really do fill in the soundscape around here.
And that goes for the other bugs, like the leaf tappers, and chick bugs. When exactly do they get here? And when do the cicadas start going?
Is it all of them all at once?
I guess I'll find out.
°¦}
https://soundcloud.com/snoozefestaudio
But that would be an oversimplification of such a migration theory.
My focus would be on North and South America. But before we look at that, we should note that crickets exist on every continent but Antarctica.
The family Gryllidae, the crickets, in the order Orthoptera, evolved between 200 and 250 million years ago... on the supercontinent of Pangea. So they were well established everywhere before the contintents moved to their current global positions.
If we assume that crickets thrive year round within ten degrees north and south of the eqator, then in the Americas... that's most of the Amazon rainforest.
Across the Atlantic, that's the middle third of the African continent... that's the Congo.
Even further east, that's the islands of Malaysia, Indonesia, New Guinea, etc... between China and Australia.
So my annual crickets, here in Illinois, are, according to the migration theory, coming from the Amazon!
There, between 10N lat & 10S lat, they live year round. But they're never ONLY in that band.
If we start at the March 20th Equinox... start of spring for the northern hemisphere, and start of fall for the southern hemisphere...
Then their population extends as far south as Argentina, way down in southern South America.
They are beginning to die off in Argentina, because it's getting a bit chilly. But at the same time, their population is beginning to spread northward out of the Amazon, up into Central America... Panama, Costa Rica, Nicaragua.
As we move through April and May, their numbers are dwindling fast in South America, but now they're expanding through Mexico, up into the United States.
And so it goes until the September 21st Equinox... start of northern hemisphere fall, and southern hemisphere spring.
By September 21st, they may not exist much further south than the Amazon, but their population extends north up into Canada, and the southern coasts of Alaska.
So, crickets are always alive and well, in about a 120 degree swath, north and south... which is huge! One degree of latitude is 69 Miles, so that's 8,280 Miles, or 13,325 Kilometers.
It's just that the 8200M N/S swath drifts north and south of the equator over time. In March, it's mostly in the southern hemisphere, in September, it's mostly in the northern hemisphere.
The crickets of the Amazon, ten degrees north and south of the Equator, are the only ones that never die out. In the areas outside of that band, they arrive and stay, until it's too cold and then they die.
The eggs stop hatching under 65F. But the adults can stay active down to 45F. Once it drops below 35F for a few days in a row... that's it!
Migration theory says the area's been sterilized completely, and won't be repopulated until new crickets from the Amazon make their way back... by hopping!
Now, even the above description is simplified. Crickets probably do exist year round at a little more than 10 degrees north and south of the Equator, especially in coastal areas that stay warmer longer.
And the speed of their migratory spread would depend on geography. So, for example, they make it up through Central America pretty quickly, because it's a narrow corridor. Wheras, once they get north out of Mexico, there's the whole huge expanse of North America to fill in, east and west.
That's, I assume, why they can make it up to, say Texas, a month after the equinox (April 20th) but it takes another three months to get up into Chicagoland in August!
Or at least I think it takes until August!..
Since I will be sooo bored this July... thanks to no wind for wind chimes, and living in the hole where no storms come through... I guess I'll just take notes as to exactly how the crickets really do fill in the soundscape around here.
And that goes for the other bugs, like the leaf tappers, and chick bugs. When exactly do they get here? And when do the cicadas start going?
Is it all of them all at once?
I guess I'll find out.
°¦}
