Slowly wrapped in gossamer threads   1 comment


Felipe del Bosque Blog Sept 2 2010

Temp High 89°F  Low 72°F          Precipitation 1.05 ins

Today was a little more typical of what we should be expecting weatherwise for September at Bosque del Cabo.  It started off raining, actually it continued raining from last night, it rained all day and it is still raining now.  It is not the heavy torrential rain that one associates with the 6 pm downpour, but rather that fine indistinct line between drizzle and mist with an intermittent heavier shower.

All of this makes for a very atmospheric feel to the forest and the grounds.  The trees are visible but appear almost phantom-like in a gloomy half light, obscured by mist.  It is as if you are looking at a picture with the color removed, a grayscale image.

The dingy conditions, though, did not deter some intrepid visitors who wanted to accompany me on the “Primary Forest Tour”.  The vegetation is always going to be there, so finding all things botanical to talk about is not a problem.  The dim, murky conditions, however atmospheric for us, seemed to dampen the enthusiasm of the animal life.  Mammals and birds are not easy to see in a rainforest under the most optimum of conditions.  Have you ever wondered why, when people come to the tropics to see tropical rainforest birds, birding guides don’t take them into the forest?  It is because vision is limited to about 15 feet in front of you.  Your view is hindered by lots of tree trunks, branches and leaves.  The irony about watching rainforest birds is that it is done in open areas where the trees have been cut down.  Now add to that a heavy mist and you don’t have conditions conducive to a lot of sightings.

But you never know what will turn up and this morning as we wound our way along the muddy trail through the dank forest, bumbling along at its own pace coming from the opposite direction towards us was a Tamandua, otherwise known as the Collared Anteater, (Tamandua mexicana).  Now, although they are not rare, it is also not that common to see a Tamandua.  Along with armadillos and sloths, the anteaters constitute the mammalian order: Xenathra.  One trait, apparently shared by all the Xenathra is; what would appear to be an ostensible lack of awareness for their immediate environment.  I have stood still in the forest and had sibling quads of Nine-banded Armadillos running back and forward over my feet without any fear, I doubt if they even knew I was there.  In the past I have walked alongside a Tamandua, that has remained oblivious to my presence until I accidently stepped on a dead twig, the snapping of which sent it unhurriedly up a tree, only for it to stop about 4 feet off the ground and lift its nose, smelling the air to see if I was still in the vicinity.  And so it was this morning, four people standing on the path and up it came, intent on its own business, searching for a meal of termites, (despite being called anteaters, they prefer a diet of termites), walked straight past us and on to wherever it may have been going.  This was a repeat performance of last night, when I had a Nine-banded Armadillo trundling along in front of me and displaying a complete lack of awareness as to my proximity.  In evolutionary terms I sometimes wonder how they made it this far along the line.

Philip is a biologist, writer and photographer as well as the onsite naturalist guide at Bosque del Cabo Rainforest lodge on the Osa Peninsula, Costa Rica.

http://www.bosquedelcabo.com

Photo Feature

If you can’t find anything to photograph, look for spiders.  They come in all sorts of shapes and sizes, some that we consider a typical spider and others more weird and bizarre.  Spiders are the eighth most numerically named group of animals on the planet.  You should also be able to find them irrespective of the weather conditions.  Spiders in webs make a good subject, especially if a breeze is not blowing, making the task of focusing on a moving object close to the lens a little difficult, if not impossible.  Placed motionless in the centre of a web is where an orb spider will normally sit unless disturbed.  That means, if you can avoid touching the web, you should be able to get pretty close.

Orb spiders are some of the more evolutionary advanced of the arachnids.  Spiders are posed with two big problems, how to catch prey and how to consume it.  Several groups of arthropods have evolved the use of silk.  People think primarily of butterflies and moths, the caterpillars of which will use silk to make cocoons, (silk comes from Silk Moth caterpillars), or hold the chrysalis to a leaf or twig.  But nothing has perfected the use of silk to the imaginative and creative extent of the spiders.

Silk is a protein.  It can be constructed from two forms of amino acid, a very loopy amino acid which can make it very elastic, or a crystalline amino acid which can make it very rigid.  In the silk glands of the spider, silk is a liquid, once the spider creates a silken thread, it becomes a solid.  Once silk is a solid, it stays a solid, the process cannot be reversed.  Silk is very elastic; it can be stretched to 300 times its own length before it snaps.  It can have the tensile quality half that of the finest steel.  Finally, if you were to take a strand of silk and let it float on a breeze, it would drift 50 miles before it broke under its own weight.  So, all in all, an absolutely amazing and versatile material.

Orb spiders have the ability to spin up to eight different kinds of silk.  To construct a web, the orb spider first spins a rigid silk which will form the framework.  It then moves from the centre to the outside attaching radial lines.  Now it moves in a circular fashion from the inside to the outside spinning a silk which when produced, absorbs water and becomes sticky.  The trap is now set.

If the web was taut, an insect the size of a large beetle hitting it at high speed would just be bounced off.  The fact that the silk is elastic allows the web to give, thereby removing all the kinetic energy from the impact, it then recoils and the prey is caught in the sticky silk.   That forceful contact will cause vibrations; the spider twangs the radial lines to locate the prey’s whereabouts, quickly goes down, wraps the unfortunate victim in silk and then delivers the poisonous bite.  The venom is a neurotoxin which will quickly quell the struggling of the now silken enwrapped meal.  The food parcel is placed in a part of the web where the prey will be digested within the confines of its own skin by digestive enzymes injected at the same time as the venom.  When the prey is ready to eat, the spider, sticks in the chelicerae and sucks out the liquid soup.

There are some animals though, that have evolved the means by which to escape their seemingly inevitable doomed entrapment.  Butterflies and moths are Lepidoptera, which means “Scaled wings”.  If you look at the wings of butterfly, you will find it is covered in tiny little powdery scales.  If you handle a butterfly you will find the scales come off in contact with your fingers.  If a butterfly or moth lands in a spider web, the scales shed from the wings allowing it to slide down over the web surface and away to freedom.  That is, if the spider is not too quick to detect where they are in the web, otherwise they will share the same ultimate fate as any other insect unlucky enough to have flown into that silken trap.

Text and Photographs are taken from the forthcoming book:

The Natural History of Bosque del Cabo by Philip Davison

Species List for the Day

Mammals

Howler Monkey

Spider Monkey

Capuchin Monkey

Agouti

Tamandua

Birds

Red-lored Amazon

Scarlet Macaw

Grey-necked Woodrail

Chestnut-backed Antbirds

Black-hooded Antshrike

Chestnut-mandibled Toucan

Golden-hooded Tanager

Cherrie’s Tanager

Mourning Warbler

Southern Beardless Tyrannulet

Great Tinamou

Yellow-headed Caracara

Roadside Hawk

Black Vulture

Reptiles

Basilisk

Pug-nosed Anolis

Golfo Dulce Anolis

Northern Cat-eyed Snake

Amphibians

Marine Toad

Red-eyed Green Treefrog

Banana Frog

Milky Frog

Smokey Jungle Frog

Fitzinger’s Rainfrog

Tink Frog

Black and Green Poison Dart Frog

Butterflies

Antirrhea philoctetes

Eurema albula

Heliconius erato

Heliconius hecale

Heliconius sapho

Morpho menelaus

Pierella helvina

Pierella luna

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Posted September 3, 2010 by felipedelbosque in Philip's Nature Diary

One response to “Slowly wrapped in gossamer threads

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  1. Phillip, I am writing this for my grandson Jack, who is Kim’s sister, Presley’s son. He loves this post the best. Spiders are one of his favorites. He is seven and is most anxious to come to Bosque and met you and see all the animals he can. Keep writing and telling him and others all you can about the amazing creatures at Bosque in the Rainforest.

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