Slo Mo Drop to a Silken Retreat   1 comment

Felipe del Bosque Blog May 30th 2011



Continuing Wet

The rains continue to fall and are now building in intensity and frequency.  The daily maximum and minimum temperatures are lowering too.  It may seem hot and humid for anyone not used to tropical conditions with the daytime temperatures reaching 87°F but being out in enduring rainfall can also give the feeling of being colder than it actually is.

Slow Drop

Earlier this year, several female Three-toed Sloths were seen around the grounds of Bosque del Cabo carrying infants.  The young sloths have now been weaned and  gone their separate ways from the mothers, as we have had recent sightings of juveniles at a number of different locations around the grounds.

One morning as I headed out on the Primary Forest tour with a young couple, we took a short detour to see a young sloth that I had seen earlier.  Little more than an hour before, as I walked through the forest, there was a juvenile Three-toed Sloth about 4 feet off the ground on the side of a small sapling.  When we returned, the youngster had made its way up to the top of the tree.  The people I was with were happy to take photographs of it slowly trying to move from the top of the tree from where it had nowhere else to ascend, into the branches of a neighboring tree.  In slow, typically languorous fashion it reached out take hold of a thin tree limb.  As it tried to transfer its weight, the branch snapped and the young sloth came tumbling down from about 20 feet up.  The young couple were concerned as to its chances of surviving a fall of that distance, especially as it hit several other branches on the way down.  If nothing else they are pretty resilient, so I picked the sloth up off the ground, and placed it back on the small trunk and up it went, none the worse for the experience.

Sloths are leaf eaters with a very low basal metabolism.  Leaf, at the best of times yields very little energy, hence the sloths relative lack of rapid mobility.  During periods of the year when there is no fresh leaf available for food, just old, fibrous, almost indigestible leaf, coupled with a temporal, an extended period of heavy cloud cover, lower temperatures and no sunlight, the sloth can succumb to a condition akin to hypothermia.  The sloths low metabolic rate, with none of the sun’s energy to help kick along the digestive processes, makes them soporific and it is at this time of year that they fall from trees, occasionally not being as fortunate as our youngster, they don’t survive the drop.

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.

 Photo Feature

Following The Silk Trail

Spiders provide an endless source of fascination.  They don’t top everyone’s list of favorite creatures, but looked at objectively, every aspect of their lives is simply incredible.  Over the past week as I have been walking around the lodge grounds, I started to see variations on an arachnid theme.  I don’t know what made me suddenly seem more aware of our eight legged friends, possibly being out late one night and seeing an Ogre-faced Net-casting Spider did it, but I was inspired to go and get the camera for a closer look.

The first things I thought I might get some shots of were the webs.  Webs, their construction and use, would provide enough material for a book in itself.  Although not obvious to the untrained eye, the web of each species of spider is unique to that species. The webs are made of silk, which in itself is an amazing material.  Silk is a long chain protein molecule.  In the silk glands of the spider it is a liquid, when the spider starts to spin, it becomes a solid, a process that cannot be reversed.  Orb spiders have the ability to spin 7 kinds of silk, of which, at least 4 varieties are used to construct the typical orb web.

Golden Orb Spider

The silk is produced by glands in the spider’s abdomen which, under increased blood pressure, exude the liquid silk.  The legs of the spider pull the silk, aligning the molecular structure, and the silken strand is created.  Take a close look at the hind end of a spider and you will see the spinnerets which produce the silk.  These are composed of a collection of muscular nozzles which can alter the properties of the strand, making it thicker, stronger and more elastic depending upon the purpose of its use.

Golden Orb Spider Spinnerets

Orbs are not the only type of web though; there are tangle webs, sheet webs, dome webs, lace webs, basket webs, reduced webs and finally the single strand that is the web of the Bolas Spider.  Spiders can also use silk to tie two leaf edges together when making a shelter. It is highly unlikely that for any day in the life of a spider it is not producing, using or in contact with silk.

Micrathena sp

Having said that, not all spiders make webs, some are active hunters while others are sit and wait ambush predators.  A typical ambush spider seen all around the grounds of Bosque at night is the Wandering Spider.  They can be found lying motionless on the leaf surfaces at night waiting for an unsuspecting small animal, be it another spider, insect, small frog or lizard, upon which they pounce, inject with venom and consume.

Wandering Spider

Crab spiders will sit, quite often superbly camouflaged, on or near a flower head.  Approaching insects are totally unaware of the hidden danger lurking amongst the blooms and as they land the spider lunges forward and captures its prey.  This particular individual I only noticed because of the silk securing the two edges of a bent leaf making a shelter.

Crab Spider Shelter

Crab Spider

There are Jumping Spiders which tend to be very small.  One of the four pairs of eyes, the forward pointing pair, are very large, giving the spider excellent sight and good depth of vision.  Whereas Wandering Spiders tend to be nocturnal, the Jumping Spiders are diurnal.  They are stealthy sneakers, creeping up on the intended insect victim, and then jumping, anything up to 20 times its own body length to land on top of its prey.

Jumping Spider

tangle webs are created by attaching a complex of silken lines between two leaves lying horizontally one above the other.  If an insect flies into the tangle it becomes stuck to the threads which break from their lower attachment, then recoil upwards towards a denser mass of threads, effectively immobilizing and holding the prey bound within its core until the spider arrives to dispatch it.

Tangle Web

Webs are familiar to most people, strung as they are in almost any location, both inside and out.  The silken threads composing the web are covered in tiny droplets of glue which, in a similar fashion to the tangle web, holds the insect momentarily captive until the spider quickly locates it, wraps it up in a different kind of silk and finally delivers the lethal injection before consuming it.

Silver Orb Spider

Text and Photographs are taken from the forthcoming book:

The Natural History of Bosque del Cabo by Philip Davison

Temperature and Rainfall

Average Daily Temp High 87°F.  Average Daily Temp Low 74°F.

Average Daily Rainfall 0.51ins.  Total Weekly Rainfall 3.58

Average Daily Temp High 30.4°C.  Average Daily Temp Low 23.2°C.

Average Daily Rainfall 13.0 mm.  Total Weekly Rainfall 91.2 mm

Species List for the Week


  • Howler Monkey
  • Spider Monkey
  • Capuchin Monkey
  • Red-tailed Squirrel
  • Agouti




  • Red-lored Amazon
  • Scarlet Macaw
  • Great Currasow
  • Roadside Hawk
  • Lineated Woodpecker
  • Black-hooded Antshrike
  • Chestnut-backed Antbird
  • Short-billed Pigeon
  • Red-capped Manakin
  • Chestnut-mandibled Toucan
  • Great Tinamou
  • House Wren
  • Black Vulture
  • Turkey Vulture




  • Barred Ameiva
  • Four-lined Ameiva
  • Green Iguana
  • Golfo Dulce Anolis
  • Clawless Gecko
  • Mediterranean House Gecko
  • Cat-eyed Snake
  • Terciopelo
  • Tropical Bird-eating Snake




  • Marine Toad
  • Red-eyed Green Tree Frog
  • Banana Frog
  • Masked Smilisca
  • Milky Frog
  • Small-headed Frog
  • Smokey Jungle Frog
  • Stejneger’s Dirt Frog
  • Black and Green Poison Arrow Frog
  • Fitzinger’s Rain Frog
  • Tink Frog




  • Anartia fatima
  • Cupido comyntas
  • Detritivora gynaea
  • Dryas iulia
  • Eueides lybia
  • Heliconius cydno
  • Heliconius erato
  • Heliconius hecale
  • Heliconius ismenius
  • Heliconius sapho
  • Heraclides cresphontes
  • Hermeuptychia hermes
  • Hyalyris excels
  • Laparus doris
  • Magneuptychia libye
  • Mechanitis polymnia
  • Morpho helenor
  • Morpho Menelaus
  • Pareuptychia ocirrhoe
  • Parides erithalion
  • Philaethria dido
  • Phoebis sennae
  • Pierella luna
  • Pyrgus oileus
  • Urbanus simplicius
  • Urbanus tanna




  • Astrocaryum Palm Fruiting
  • Black Alligator Tree Fruiting
  • Calabash flowering and fruiting
  • Clusia Vine Fruiting
  • Monkey Comb Tree Flowering and Fruiting
  • Candlestick Plant Flowering.
  • Cannonball Tree Flowering
  • Figs Fruiting
  • Inga Fruiting
  • May Tree Flowering
  • Manglillo Fruiting
  • Nutmeg Fruiting
  • Psychotria Fruiting
  • Rosa del Monte Flowers
  • Rubber Tree Fruiting
  • Santa Maria Flowering
  • Stinky Toe Fruiting
  • Ylang ylang Flowering


One response to “Slo Mo Drop to a Silken Retreat

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  1. Great post Philip. Love the shots of the spiders.

    Spending about 1/2 hour with one of the juvenile sloths you mention was the highlight of our recent trip. We watched it climb down to the ground to take care of business and then climb back up again. All the while it would glance in our direction from time to time so we got really good looks at it. It was another great experience at Bosque del Cabo.


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