in StemSociallast year (edited)

Last week, while walking across the meadows at the edge of town, just after the last houses ...

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... I encountered some fuzzy caterpillars ...


... a long line of fuzzy caterpillars, to be more precise.

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They were walking across the parchment of terrain with very sparse vegetation ...

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... directed to the place covered with dense short grass.

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These are the larvae of the Thaumetopoea pityocampa moth ...

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... commonly known as the Pine processionary. And now, before continuing the story about this interesting species, is time to take a look at caterpillars in motion, in the video I recorded last week, at the edge of town. Have a good viewing.

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A look at the social behavior of the Pine processionary caterpillars. Just like most of my videos, this makes much more sense as a part of the considerably longer article on HIVE, than as a standalone thing. You can find more information about this interesting species if you read the post.

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As you could see in the video, when they reached the grass ...

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... the caterpillars changed their formation ...


... the line became a seemingly less organized pile ...

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... hidden in the grass.

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From what I learned on the Internet while preparing this post, this could be the definitive end of the procession ... because the Pine processionary caterpillars pupate in the soil, about 10 cm deep, and they start the pupation at the end of winter or early in spring. It's quite probable that the caterpillars dug their way into the ground and disappeared from sight while I was walking home.

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While they are crawling along the host tree in search for a good feeding place, the caterpillars lay down a pheromone trail from the tip of the abdomen. Although the caterpillars also secrete silk and mark their pathways on the branches and twig with those threads, this plays little or no role in trail following. Most likely, silk helps the caterpillars grip on smooth surfaces of the plant.
They can distinguish old from new trails, and tend to follow trails marked by larger numbers of caterpillars. This trail marking enables the caterpillars to aggregate at feeding sites and allows them to find their way back to nest after feeding. When they move over the branches, caterpillars may travel head to tail in small groups or alone, and they rely on the trail marker to find their way.
However, during processions the system works in a slightly different way, stimuli from the bristles on the tip of the abdomen of the caterpillar in front serve to hold the line together, taking priority over the trail pheromone. An experiment showed that the caterpillar can easily be induced to follow a model made of a wooden dowel covered with the abdomen of a killed caterpillar.

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The large meadow was surrounded by shrubs and pine trees ... the caterpillars probably descended from there. On the following photograph ...

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... you can see the nest of the Pine processionary caterpillars.

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The silk at the bottom is decorated with excrements ...

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... and old molts.

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I took these shots a few days later, about 5 kilometers further, near the neighboring village of Liznjan, on the harsh stony terrain at the edge of an abandoned stone quarry. Only small pines grow here. This one was just slightly taller than me, so I could easily explore the large cocoon ...

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... and find this amazing little spider ...

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... the Kochiura aulica.

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A few spiders of this minuscule species have found a nice shelter on the surface of the nest built by caterpillars ...

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... and when you see them crawling or resting among these threads ...

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... it could look like they built the whole thing :)

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The caterpillar Colonies inside the nests are active throughout the winter months.

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Infrared activity monitors during some studies, have shown that the caterpillars leave their nests soon after sunset and travel to distant feeding sites on the branches of the host tree. There, they feed overnight then return to the nest at dawn. The caterpillars have been observed foraging on the coldest nights and can move at sub-zero temperatures. The nests are positioned so that they can be warmed by the sun. The caterpillars rest during the day and the heat in the nest helps them digest the food. When they emerge from their nests in late March, they are fully grown and leave their nest processing towards pupation sites in the ground.

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Here you can see the small spider near the big molt of a Processionary caterpillar ... or a corpse of the Processionary caterpillar ... I'm not sure ...

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... I took all these shots with the flash on ...

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... because the day was very cloudy ... and the evening was approaching ... and although this kind of light source makes all the details visible, when it comes to aesthetics - well, the photographs don't convey the atmosphere and lack the poetic elements that more subtle natural light can bring.

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Fortunately, just before leaving the spiders and caterpillars to their usual activities ...

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... I found this angle ... with the sky as the background ...

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... that, with a bit of patience, enabled me to take these more natural - looking shots and show you the real atmosphere on that cloudy day.

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And that's it. The procession is over. As always in these posts on HIVE, the photographs and the video are my work. I found some information about this interesting species in the pretty long Wikipedia article, and some stuff I knew from before, from various natural history books that I read who knows when, probably when I was a kid.


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Impressive pictures!
Here, further north, it is mainly the Oak processionary that is on the move.
Wherever it is found, everything is immediately cordoned off and warning signs put up. The poison of these caterpillars attacks the human immune system and can lead to many problems.
I hope you didn't get too close to them, because the same probably applies to your caterpillars ;)

I knew that these Pine processionary have hair and bristles that can create problems to the health of humans and other animals ... but the reaction varies a lot ... fortunately :) my reaction is minimal, I can get very close to them and nothing happens ... only when I accidentally touch them, like I did while recording the video, the touched place starts to itch and slightly burn. It didn't last long though, so it's ok, the price paid for the video wasn't too high.
But the next time, who knows ... this kind of reactions can change in time, so I think I'll let them be next time ... unless something really extraordinary, that just has to be recorded, happens in front of my eyes :)
It seems that here in my area the Pine processionary and the pine trees exist in a relatively good balance, I see some nests here and there and the trees are still prosperous.

Wonderful caterpillar (and spider) shots. I've read about the processionary caterpillars. Some people have had serious allergic reactions to them, and serious eye problems because the hairs can float through the air and get embedded in the eye. Sorry for that unpleasant note to your wonderful blog. You probably know all this already :)

Hehehe :) It's ok, this is all part of the charm of this species. There is a bit of potential danger related to these caterpillar, so the problematic hair and allergic reaction must be a part of conversation. It's like talking about a venomous snake and not talk a bit about what its venom can do.
It's a very sophisticated and effective protection against predators ... and they develop this highly irritating mechanism only when almost ready to pupate. "At the fourth and fifth instar stages, their tegument comprises two different kinds of hairs: true non-removable hairs and removable urticarial setae" ... so this is a protection specifically for their procession adventure that brings them in the open, before that they rely more on their nest and secretive nighttime feeding to avoid the troubles.

Thank you for that expanded explanation :)


Add dark tones and get a horror movie!


That was truly fascinating... thanks for taking us along on this processional!

Very strange creatures which we don’t have here! They look quite smart to me! My eyes wouldn’t be able to focus on such tiny creatures with colours if the earth! LoL
You must have laser sharp eyesight!

Hehehe I have laser sharp eyeglasses :D for watching the things up close

Oh! I will have to ask my optician to find me some laser eyeglasses!! This would be very useful!! LoL


Oh, I hope you didn't touch the nest or them. It can be toxic, really dangerous can be. My friend had to go the hospital because of the reaction.
For dogs, sometimes life treating if they get in touch with the Pine processionary caterpillars.

Btw, they are beautiful, on the photos :D and your video is awesome, those close shots are great...and the way of explication :D hehehe

I'm lucky when it comes to these caterpillars :) they don't cause me breathing problems and other dangerous reactions, just a bit of itching on the skin if I touch them by accident ... fortunately with the nests :) the things are even better for my health ... I had to hold the nest with one hand while photographing the minuscule spider with the other, and everything was ok ... fortunately ... this time ... I read somewhere that this is never granted, and if I had no problems this time, I could have them during another close encounter in the future ... so, this is probably my last post about this subject :)

Last post about the subject 🤣

But that is good, if you don't have reaction, just itching on the skin. You are lucky 😉

Here, if you see a nest you can call the town hall and they are supposed to sent someone to take it away from the tree before the carterpillars come out.

When my son was lot smaller, he had a reaction that we think it was maybe connected to those processionary carterpillars. We went to a pine forest and spent a day there (It was February or March). We saw the nests, but didn't touch them. Even then, he had red spots in his arms and back when we came home..

Anyway, very good post, didn't want to ruin it with the toxic thingy of those creatures :))

:) Their toxicity it's a cool topic for a casual conversation :D

, I mean da, it was cool to talk a bit 🙂


Wow impressive Pictus End good shot creatur & writing story ;))

Hehe :) thanks

Really admire the beautiful colony of caterpillars and spiders and also take your photo shots sir @borjan

That's a rather beautiful procession. Good shots!

Thanks :)

Wow how you found these?

I just encountered them while walking. They are very common here.

Your photography makes these guys seem like monstrous aliens. Love it!

Hehe, like an alien invasion in some Ed Wood's movie. :)