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Drops of Colored Poison on a Leafy Bed   Leave a comment

Felipe del Bosque Blog February 11th 2013

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The Patter of Tiny Feet

The dry conditions continue but with the bonus of some rain at night which is enough to keep things green.  That hint of dampness is enough to tempt the Halloween Crabs, (Gecarcinus quadratus), out from the dark dank tunnels in which they reside beneath the surface of the forest floor.  They may be land crabs but they breathe through gills which have to remain moist to function effectively, so even though they may have escaped the confines of their aquatic environs and adopted a terrestrial habit, they have not fully adapted to totally dry conditions.  It always remains something of a surprise for people who had never heard of land crabs, and consequently only associate these crustaceans with the rocky coastal shorelines, to find the forest floor crawling with them following a summer shower.

It is not only those creatures in possession of 10 legs that have been spurred into action; the six-legged life forms of the social kind have suddenly become more obvious by their untiring activities.  Leaf-cutter Ants, (Atta cephalotes), familiar to most visitors to Bosque del Cabo due to the mesmerizing lines of slightly wavering fragments of leaf being carried in what seems like a slow moving river of green through the lawns and across the forest floor, have caught a second wind.

Normally at the height of the dry season the Leaf-cutter Ants cease their assiduous cutting and carrying during the daylight hours and recommence once the sun has set.  The dry season in the south west of Costa Rica can quite often result in very little rain for five months of the year and sometimes none at all during February and March.  At this time of year, should the ants cut and carry leaf, the distance over which it has to be transported and the time required to do so can result in the leaf drying out.  If the leaf contains small quantities of toxic compounds, as it dries these may become more and more concentrated thereby constituting a lethal cocktail for the ant or the fungus grown on the leafy mulch that provides staple diet of the ants.  This time of year those leaves delivered to the nest that were tasted and recognized as being unsuitable by the quality control ants are brought back to the surface and dumped on top.  The further we go into the dry season, the higher these mounds of dried leaves will built up around the entrances of the nest.

Leaf-cutter Ant

Currently the waste disposal ants in the colonies seem to be hard at work too.  In many of the nests around the trails excavation has been taking place at a heightened level of activity.  If you were to walk the trails on a daily basis you would see the heaps of earth accumulating in ever increasingly sized mounds.  Take a closer look and you will see the ants whose allocated employment is to remove excavated earth and waste products from inside the nest and bring it to the outside.  Each one is carrying a fragment larger than her own head.  Where the waste tip issues from the side of a hill or bank you will see the friable piles tumbling down, in ant terms each mouthful the size of a boulder, to the base.

Feeding of the Ravenous Hordes

The leaf-cutters are not the only ants that have been stimulated into action over the past week or so.  At various points on several trails long columns of ants moving quickly, deliberately and determinedly have been seen.  These are army ants, (Echiton spp), one of the forests most formidable mini predators.  Army ants have no nest, they are nomadic.  They have to periodically change the location of their temporary headquarters due to the fact that being such a super efficient predator, were they to remain in any one area for a protracted period of time they would deplete the locality of all small forms of life.

They may be encountered in one of two phases of activity; translocation or foraging.  When on the move to a new hunting area the whole colony including the queen is on the march.  There appears to be an endless river of ants streaming across the forest floor, insects in fluid form.  The workers carry the immobile pupae like swaddling aliens in their mandibles.  When virgin territory is reached the army ants ball up, linking their legs together to form a living bivouac, generally somewhere in a sheltered spot such as a hollow log or under a large fallen branch.  The queen moves to the centre, swells up and starts to lay about 60,000 eggs a day.

When the first larvae emerge, they emit a pheromone which causes a change in the behavior of the other workers.  They are stimulated into a hunting response which results in the mustering of half a million murderous assassins swarming through the forest slaughtering all that find themselves so unfortunate to be in their path.  The ravenous hordes surge relentlessly across the forest floor, up trees and scouring every nook and cranny.  The foraging front can be anything up to 60 feet across and 3 feet in breadth.

Army Ant

The ant’s progress will be heralded by flocks of exciting birds gathering as if at a tickertape parade.  You will hear the calls of antbirds, ant-thrushes, antwrens, woodcreepers, woodpeckers and tinamous.  If ever you see Grey-headed Tanagers you will see army ants, they are obligative followers of the army ants.  None of the birds are here to eat the ants.  As the front moves forward so many creatures are flushed, fleeing for their lives only to meet their end in the bill of a hungry bird.

Even if they escape those two terminal hazards, a third gruesome fate may await.  Clouds of parasitic flies, Phorid flies are flying in droves at the head of the advancing front.  The hum of their countless buzzing wings can be heard in the air.  They fly in and lay an egg on any victim attempting to escape the melee of death beneath.  The fickle hand of fate has played them a cruel hand.  They may have escaped mandibles, bills and jaws but the insidious cargo they now carry will now become their executioner.  When the egg hatches the fly maggot will eat its victim alive.

The ants push forward, unrelenting in their pursuit of fresh meat.  Whatever they come across they have, spiders, scorpions, centipedes, beetles, cockroaches, crickets, small frogs, small lizards, small snakes and even fledgling birds, it matters little to the ants.  There is no hiding place; the only choice is to run.  Once found, the prey is overwhelmed in a seething mass of frenzied killers, the ant’s venom laden stingers plunging through the victim’s skin time and time again and within seconds it will have been done to death.  Then it will be butchered on the spot, the slashing mandibles of the ants acting like meat cleavers to dismember the cadaver.  The separate parts of its now mutilated corpse will be carried back along feeder columns from the foraging front to the bivouac to feed the hungry carnivorous larvae.  Once the larvae pupate, the hunting response is turned off and away they go nomadically through the forest until they reach new and rich killing fields from which they will steal the lives of countless unfortunate creatures now dwelling there in blissful ignorance of their rapidly approaching fate.

Swollen With Indignation

Snakes are never the easiest animal life form to find in the forest.  They are ever-present but tend to elude those who want to see them but ironically make an appearance for those who don’t.  As with everything else, once you overcome your aversion to these reptiles, then they become fascinating creatures evolutionarily modified for a unique legless life-style.

One reasonably common snake around the grounds of Bosque del Cabo is the Neotropical Bird-eating Snake, (Pseustes poecilonotus).  They can grow up to six feet or more in length, are a pale blue-grey in color with a yellow belly and quite often a dark head.  If approached they put on a defensive display that involves flattening the neck laterally and turning the head side on so that they look larger than they are.  They are also very snappy snakes and are inclined to readily strike out and bite if molested, a characteristic of both juveniles and adults alike.

Tropical Bird-eating Snake

As the common name suggests, the bird-eating snake feeds on chicks and eggs from nests.  The breeding success of many birds at Bosque is hampered by these lithe predators whose forked tongue allows them to locate the presence of prey very quickly.  Many times around the restaurant area where Cherrie’s Tanagers and House Wrens nest and raise their offspring, it is almost a certainty that before too long the bird-eaters will turn up.

Pseustes poecilonotus

This individual I happened across this week when returning to my cabin.  It was lying across the path and I could see it ahead so just stood and watched for a while.  Its tongue was flicking constantly in and out tasting the air for scent particles.  It moved very slowly its head face down intently following what seemed to be a trail across the ground.  Then it lifted its body and flattened its neck, still its tongue rapidly flicking to taste the air and leaf litter in front as if something was bothering it.  I could see no sign of other life.  It looked like its attention was going to be held in this area for a while so I fetched the camera, lowered myself to the ground and took some close ups of its head before letting it slowly slither off into the undergrowth.

Unexpected Visitors

As the forest is so full of life it is no surprise that things turn up all over the place all of the time.  If I was to sit on the patio of my cabin and take time to look around I will see a myriad of small animals each one of which can capture your attention and then hold you thrall to its actions which can be observed, noted and later analyzed.  It may produce nothing more than an air of idle curiosity but when you delve a little deeper then most subjects however large or small have a fascinating life history and natural biology.

Jumping Spider

This week I was sat reading in the shade and noticed a line of minute ants making their way up and down the outside wall of my abode.  They were little more than moving specks and in typical ant fashion were following in a fairly strict line in both directions.  There was nothing unusual in this per se and my attention was concentrated more on where they were coming from and consequently where they were going to before returning again.


Off to one side of the ant column was another small dark speck that I could make out as having eight legs.  Tiny as it was, its form and behavior suggested that of a jumping spider, Family Saltacidae.  As I sat watching a small drama unfolded.  One of the ants broke ranks and the maverick spirit took a line of its own deviating away from the main caravan.  This was to be its undoing.  Small prey attracts small predators; nature is red in tooth and claw at every size level.  This ant that had left behind the safety in numbers that comes with a being part of a group had now exposed itself as a target.  That error did not escape the attention of the spider.

Jumping Spider

Despite its minute dimensions, the jumping spider is an evolutionarily adapted hunting and killing machine.  Looking at it face on you will find the front of the head bears huge eyes which in spider terms are visually acute.  It’s not very often that the spider prey will see these eyes as the jumping spiders are as stealthy as a cat.  Once they have singled out their victim they sneak up on it at the last moment launch into the air landing on the hapless prey.  Needle sharp chelicerae inject a powerful immobilizing venom and digestive enzymes which both kill the prey as well as reducing its innards to a soup that the spider can suck from its now dead shell.

That is what happened to the ant.  It would not have even registered that anything was happening.  The attack was lightning fast.  The ant did not know what hit it and it was dispatched in the blink of an eye.  The tragedy played out on the mini stage before me was one of countless such encounters that you can witness all around if you choose to redirect the focus of your attention.

Bat Sac

Despite their numbers, abundance and diversity bats are not always the easiest animals to find.  When you do find a bat, without having it in your hand it may not always be the easiest animal to identify to species level.  Costa Rica has a very diverse bat fauna, 111 species in total of which 80 species live on the Osa Peninsula.

Some bats are so distinctive though that their identity leaves little ambiguity as to what it is you are looking at, the Greater White-lined Bat, (Saccopteryx bilineata), falls into this category.  One morning while walking on the Zapatero Trail with a group of guests, we stopped to watch two bats flitting around between the giant buttresses of the tree.  They would settle momentarily then flit off again to land not so far away.  When they did land it was face down but with the head pushed out at almost a right angle to the body.  This is the characteristic poise of the Greater White-lined Bat.  After the tour had ended I headed back in the hope of getting some photographs.  My luck was in, the bats were still there.  They were not keen on my presence and kept moving but with a little perseverance I managed to capture several images.

Greater White-lined Sac-wnged Bat

The Greater White-lined Bat is one of the sac-winged bats belonging to the Family Emballonuridae.  They are insectivorous bats and are normally communal roosters having one male guarding a harem of one or more females.  Quite often there can be several roosts in close proximity.  They are called sac-winged bats as the male has a small pouched scent gland on the wing in front of the forearm.  This emits a smelly secretion which is used in both territorial and mating displays.  The male can be seen during the course of the day flying up and down in front of the females serenading them with releasing scent from his ‘sac’.

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

Localised Poison

There are two species of poison arrow frog to be found at Bosque del Cabo; the Black and Green Poison Arrow Frog, (Dendrobates auratus), and the Golfo Dulce Poison Arrow Frog, (Phyllobates vittatus).  Both are visually unique, both have different calls and they inhabit different habitats so there should be no confusion as to what you are looking at when you find one.

Black and Green Poison Arrow Frog

Currently on the forest floor behind the restaurant where the Creek Trail enters the forest the Black and Green Poison Arrow Frogs can be seen without little difficulty.  You just have to walk ten yards or so then stop and look down by your feet and invariably you will see at least one but often several hopping around.  They are not inclined to be shy either, quite often making their way across the open expanse of the cleared trail or jumping around on the leaf litter to the sides.  The Golfo Dulce Poison Arrow Frogs can be a little more difficult to locate.  They prefer damper habitat and can be found by the creek beds.

Both species have different calls.  The black and green has a high pitched trill which is produced in a very broken stuttering fashion.  The golfo dulce calls with a long unbroken trill.  At certain times of the year you can hear the golfo dulce constantly calling but that is not always going to lead you straight to them.  They are more retiring than their black and green relatives and usually call from under fallen leaves, hollow logs or small spaces in the banks.  Also due to their inherent ability with regards to ventriloquism they seem to be in a different location to where the calls are emanating from.

The poison arrow frogs are diurnal.  For a frog to be found hopping around on the forest floor during the light of day would normally make it an easy target for predators.  These frogs have evolved toxic skin secretions to protect them against predation.  But there is little point having a toxic skin secretion if the predators are not aware of it.  If the frog gets eaten it is too late for both the frog and the animal naïve enough to eat it.  The glowing colors that they sport make them stand out clearly against the background.  If something is so deliberately drawing attention to itself it is not inviting predators to dine on it but rather warning them off.  These are warning colors, aposematic coloration.

Golfo Dulce Poison Arrow Frog

The black and green secretes a lipophilic alkaloid skin toxin which if you get it on your skin can cause burning and itchiness of cuts and scrapes.  Woe betides you if you get it on any mucus membranes such as eyes, nose or mouth.  Put two of these frogs in a bag together and they will die.  The golfo dulce is the most poisonous of the Costa Rican poison arrow frogs.  The skin toxin is a batrachotoxin which poisons heart muscle causing a painful death.  Do not attempt to handle these frogs but by all means admire them for their toxic beauty.

Text and Photographs are taken from the forthcoming book:

The Natural History of Bosque del Cabo by Philip Davison

Temperature and Rainfall

Average Daily Rainfall 0.04 ins.  Total Weekly Rainfall 0.29 ins

Average Daily Rainfall 1.1 mm.  Total Weekly Rainfall 7.4 mm

Highest Daily Temp 96°F.  Lowest Daily Temp 75°F.

Highest Daily Temp 35.9°C.  Lowest Daily Temp 24.8°C.

Species List for the Week


  • Mantled Howler Monkey
  • Spider Monkey
  • White-faced Monkey
  • Agouti
  • Alfaro’s Pygmy Squirrel
  • Red-tailed Squirrel
  • Greater White-lined Bat
  • Collared Peccary


  • Crimson-fronted Parakeet
  • Red-lored Amazon
  • Scarlet Macaw
  • Great Curassow
  • Crested Caracara
  • Mangrove Black Hawk
  • Roadside Hawk
  • White Hawk
  • Crested Owl
  • Spectacled Owl
  • Chestnut-backed Antbird
  • Short-billed Pigeon
  • White-tipped Dove
  • Blue-crowned Motmot
  • Rufus Piha
  • Long-billed Hermit
  • Red-capped Manakin
  • Chestnut-mandibled Toucan
  • Grey-headed Tanager
  • Bright-rumped Atilla
  • Dusky-capped Flycatcher
  • Black-throated Trogon
  • Great Tinamou
  • House Wren
  • Black Vulture
  • Turkey Vulture


  • Barred Ameiva
  • Cat-eyed Snake
  • Central American Smooth Gecko
  • Central American Whiptail
  • Clawless Gecko
  • Four-lined Ameiva
  • Golfo Dulce Anolis
  • Mediterranean House Gecko
  • Pug-nosed Anole
  • Tropical Bird-eating Snake


  • Black and Green Poison Arrow Frog
  • Golfo Dulce Poison Arrow Frog
  • Marine Toad
  • Masked Smilisca
  • Red-eyed Green Tree Frog
  • Savage’s Thin-fingered Frog
  • Stejneger’s Dirt Frog


  • Anartia Fatima
  • Anartia jatrophae
  • Archaeoprepona demophon
  • Caligo eurilochus
  • Colobura dirce
  • Dryas iulia
  • Eueides aliphera
  • Eueides lybia
  • Eurema albula
  • Glutophrissa drusilla
  • Heliconius erato
  • Heliconius hecale
  • Heliconius ismenius
  • Heliconius sapho
  • Heraclides cresphontes
  • Hermeuptychia hermes
  • Morpho helenor
  • Morpho Menelaus
  • Parides erithalion
  • Pierella helvina
  • Pierella luna
  • Pierella argante
  • Phoebis sennae
  • Philaethria dido
  • Pyrisitia proterpia
  • Pyrrhogyra crameri
  • Temenis laothoe


  • Alamandra  cathartica Flowering
  • Alpinia purpurata Flowering
  • Apeiba tibourbou Flowering
  • Arachis pintoi Flowering
  • Arundina graminifolia Flowering
  • Attalea rostrata Fruiting
  • Bauhinia variegata Flowering
  • Cascabella thevetia Flowering and Fruiting
  • Citrus spp  Fruiting
  • Clusia rosea Flowering and Fruiting
  • Clusia vallerii Flowering and Fruiting
  • Cocos nucifera Flowering and Fruiting
  • Crestentia alata flowering and Fruiting
  • Costus speciosus Flowering
  • Couroupita guianensis Flowering and Fruiting
  • Dypsis lutescens Flowering and Fruiting
  • Etlingera elatior Flowering
  • Ficus citrifolia Fruiting
  • Ficus insipida Fruiting
  • Jacaranda mimosifolia Flowering
  • Heliconia chartacea Flowering
  • Heliconia latispatha Flowering
  • Heliconia pogonantha Flowering
  • Heliconia psittacorum Flowering
  • Heliconia rostrata Flowering
  • Hibiscus rosa-sinensis Flowering
  • Hymenaea coubaril Fruiting
  • Hymenocallis littoralis Flowering
  • Ixora coccinea Flowering
  • Lantana camara Flowering and Flowering
  • Lagerstroemia speciosa Fruiting
  • Morinda citrifolia Fruiting
  • Musa acuminate Flowering and Fruiting
  • Nephelium lappaceum Fruiting
  • Piper auritum Flowering and Fruiting
  • Piper nigrum Fruiting
  • Piper umbellatum Flowering and Fruiting
  • Pleiostachya pruinosa Flowering
  • Plumeria rubra Flowering
  • Psychotria sp Fruiting
  • Stachytarpheta frantzii Flowering
  • Virola guatemalena Fruiting
  • Zammia sp Flowering



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