Author Topic: Arctosa perita - how does she make her tunnel?  (Read 1667 times)

Offline Arne Fjellberg

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Arctosa perita - how does she make her tunnel?
« on: July 22, 2010, 06:21:18 PM »
For the last two years I often observed Arctosa perita being active on the sandy seashores around the southern tip of Norway (Lista-Jæren), admiring her perfect camouflage and her neat retreats in the silk-spun tunnels in the sand. However, I could never figure out how she actually made these tunnels. They are usually set in the sunny slopes of the active white dunes at the beach front. Digging these out in the "floating" sand seemed impossible to me.

In late April this year, after collecting springtails at the sandy beaches near Mandal (Sjøsanden), I had my sandwich lunch behind some Leymus-dunes, in shelter from the stiff wind. Suddenly I became aware of a female perita performing a strange "dance" in a small hollow in the sand. I watched her close and realized she was actually using her spinners making a web along the edges of the hollow. I grabbed the camera and made a sequence of shots showing how she finally covered herself up in the sand pit. After spinning some threads along the periphery of the pit, she would turn around and use her legs to drag grains of sand onto the net. When the pit was almost closed, she spun silk across the opening and windblown sand made the final cover during the next few minutes. The whole process lasted about five minutes.

Well enough! But how did she make the tunnel? That covered pit could just be a night retreat or some short of shelter. While pondering over this I observed that she was still moving down there - making small "bumps" beneath the sand surface, mowing away from the primary pit. I could just imagine she was pushing away the sand while she used her spinners to reinforce the walls. Unfortunately I had no time to watch the final outcome of her underground work, but I bet she would eventually burst out of the sand having made a complet tunnel! So - probably she does NOT start with the opening. She goes into the sand and "push" her way out! Doing so we can also explain how she completes her construction with the nice "collar" of the entrance. But still I regret that I did noe spend a few extra minutes on the beach the see her COMING OUT!

(I write this in English to reach a wider audience)
(NB! the two last photos should change places in the sequence....)

Arne F.
« Last Edit: July 22, 2010, 08:19:05 PM by arnef »
Arne Fjellberg

Offline Magne Farlund

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Re: Arctosa perita - the making of her tunnel in sand
« Reply #1 on: July 22, 2010, 06:46:55 PM »
@arnef

Snakker om å velge rett sted for matpausen. Dette må ha vært morsomt å iaktta. Naturens ingeniør i aksjon, med et infløkt tunnelprosjekt. Det å utvikle rutiner for å bygge tunnel i så ustabil masse tok nok noen hundre år med prøving og feiling. Flott dokumentasjon.

Magne.


Når du går tom for nye biotoptyper å lete i så start på nytt - med andre metoder.

Offline Annie

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Re: Arctosa perita - how does she make her tunnel?
« Reply #2 on: July 22, 2010, 11:13:38 PM »
Heia Arne :)

Kjempeflott innlegg med vakre bilder :)

Veldig fascinerende aa lese om hvordan denne dama lager disse "hulene" sine! Da vi var paa Sandnes og besoekte noen av strendene der sammen med Harald, viste han oss disse hullene. Han viste oss ogsaa hvordan nettene saa ut, meget interessant :) Helt utrolig at det gaar an spoer du meg :)

Mvh
Annie
"One Act Of Kindness Can Change The World."

Offline Glenn H. Morka

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Re: Arctosa perita - how does she make her tunnel?
« Reply #3 on: July 23, 2010, 04:15:33 AM »
Wow, flott artikkel, Arne, -og hvilke fotos! :)
Slikt er artig å få med seg under ei nisterast.
Glemmer aldri første gangen jeg så peritaen. Harald sende meg et eksemplar for fotografering.
Den var mye større enn jeg trodde, -og ikke minst fargerik.
Når man da fikk se den i sitt rette element på stranda, var det litt av en opplevelse! :)
Flott at du skrev den på engelsk, slik at flere kan lese om opplevelsen! :)


-Glenn
"Sykemeldt"



Offline Kjetil Åkra

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Re: Arctosa perita - how does she make her tunnel?
« Reply #4 on: July 28, 2010, 09:53:24 AM »
Tusen takk for denne historien, Arne. Tror det er første gang dette blir så utførlig beskrevet og illustrert med bilder!!

Kjetil
Antall arter i Norge: 624!

Siste: Bjarte Aadland slo til med ett overraskende funn av Robertus ungulatus (Theriididae) på Rognabekken myrområde på Stord i november 2012.

Vårt mål: 650 arter! (26 to go!)