Can insects predict LONG TERM weather?

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Chuck
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Can insects predict LONG TERM weather?

Post by Chuck »

There's an old adage that the severity of winter can be predicted by the stripes on the Wooly Bear caterpillar. This has not been proven to be true.

But can insects predict long-term weather, e.g., the severity of winter?

I ask because up here the Tiger Swallowtails are still eclosing, and presumably ovipositing. This is a week longer than last year, though in past years I've seen them into the first week of September. IF today's ovae are to survive through pupation, figure six weeks, that means no severe weather, no frost, until the first week of October.

Do the Tigers know something, or is it just a gamble?

I did some quick research, and there's no serious answer. There is of course the old wives tales and Farmer's Almanac type stupidity. There are scientific studies but they don't seem to discern between short-term and long-term weather, and one has to read them to discover that they're focused on short-term (e.g., days or a week) - No S Sherlock, fish know the weather days in advance based on pressure.

I can predict the weather in my area too. First full week of September brings a terrible cold front and is the first day after months I wear long pants and socks. Like clockwork. Weather is not random as most think it is.

So what of these Tigers? Do they think it will be warmer than usual through October, or are they gambling?
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adamcotton
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Re: Can insects predict LONG TERM weather?

Post by adamcotton »

The pupae that resulted from larvae which failed to initiate diapause (the trigger for diapause is during the period between fourth and late fifth instar) will emerge or die trying, regardless of the weather.

It is not really a case of gambling as much as a natural 'insurance policy'. Some pupae from each generation will often go into diapause, those relatively few from the early generation which go into diapause will then hatch in the following spring along with the pupae from later generation(s). A percentage of the summer generation do not go into diapause, they naturally mate and their offspring either go through to pupae or die. If they survive they will go into diapause and hatch next spring. This ensures that at least some will survive to the following spring even if there is some sort of catastrophe in summer, hence 'insurance policy'.

Adam.
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nomihoudai
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Re: Can insects predict LONG TERM weather?

Post by nomihoudai »

The numbers of insects that hatch in a given period will create a distribution. From this distribution one can define a probability. For some species there is quite some variance in their distribution. This gives them adaptability without having to know anything about the world, seasons or climate.

In simpler words. Some insects randomly hatch here and there. Sometimes they are lucky and they can finish an extra generation. They don't know anything about long term trends and don't need to.
Lepidoptera distribution maps: lepimap.click
Chuck
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Re: Can insects predict LONG TERM weather?

Post by Chuck »

Most emergences I've seen charted are pretty much binomial distribution with a tail extension at the end.

So why would a population, instead of being binomially distributed, peak when ovipositing would have a high mortality? And, assuming the population generally peaks with plenty of time, but then one year doesn't, I'd think that over long periods (millennia) those that tend toward a late emergence would tend to be eliminated. However, and this is what I was exploring, if the population somehow were able to predict the 60 day weather, and knew it to be good, they could carry on with no greater than normal risk.

Hagen & Lederhouse did some experiments that demonstrated several factors affecting eclosion, which also might offer a solution: extrapolating their findings, I suppose a cool early summer followed by warm late summer could push out eclosion. This would be deadly to the next generation though.
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Re: Can insects predict LONG TERM weather?

Post by kevinkk »

I'd agree with Nomihoudai, insects just do what they do, and don't need to predict weather, we've all seen larva that in the same population will
grow faster than others, as well as some species overwintering more than one season. Certainly abnormal temperatures one way or the other
may be a problem, but I'd think at least once pupa are formed, especially when day length is shorter are safe from early emergences.
Over the millennia insects have probably experienced just about every climate scenario and some years may simply have fewer adults, for instance,
we had a late start to spring this year, but not late enough to prevent a generation for the following year. I did get a surprise on my last collecting
trip, a polyphemus male on July 26, at 3000 ft, even not being familiar with the area, I doubt there would have been enough time for him
to have found a mate, and the subsequent ova reach maturity. I'd have to visit the same location again to get anything close to an answer for that.
I certainly didn't expect to see a Saturniidae that late here in the Northwest.
The local weather "joke" is that our summer starts on July 5th..
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joachim
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Re: Can insects predict LONG TERM weather?

Post by joachim »

kevin are that your feet in the profile?
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kevinkk
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Re: Can insects predict LONG TERM weather?

Post by kevinkk »

joachim wrote: Tue Aug 23, 2022 10:16 pm kevin are that your feet in the profile?
Yes, that's my preferred method of collecting, kicking back in the SUV, watching a blu-ray, waiting for the moths to fly in. It's deplorably
primitive.
Chuck
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Re: Can insects predict LONG TERM weather?

Post by Chuck »

"Predict" may be a misnomer in a way. Certainly, environmental conditions (eg diurnal length and heating degree days) influence whether some populations are univoltine or bivoltine.

On the annual scale, eclosing behavior is influenced by seasons. Likely through genetic heredity, a given species "knows" not to eclose early or late. This isn't to infer cognizance, but the fact is insect populations "predict" winter and have "learned" to accommodate.

Insects can predict weather days in advance. As can fish, squirrels, and a limited number of humans.

So if insects can predict weather in the short term, and in the long term, to what level can they do so in between?
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