Monday 22nd February
Into the Oven
The temperatures have continued to remain around 40ºC (104ºF) mark for several months now. Coupled with this has been the sharp decline in rainfall from mid December as the dry season progresses. January experienced little more than one and a half inches of rainfall. It is now that the forest floor begins to take on a dry and dusty appearance and despite being only two months into the dry season small cracks have begun to appear underfoot. Not many people complain of the blue cloudless skies though which give day long bright and sunny conditions.
Two animals have been seen in the area over the last week that are not frequently seen. The Brown-throated Three-toed Sloth, (Bradypus variegatus), is a reasonably common rain forest mammal. It would not be unusual to see one in the area given their relatively high density of numbers. The problem is that they live at the tops of the trees, don’t move too far or too fast and have a fur that is tinged green with algal growth ensuring that it does not stand out but rather blends in. That is a situation that lends itself very nicely to an animal that cannot move too fast in an effort to escape predation.
There is a second species of sloth that inhabits the area though; Hoffman’s Two-toed Sloth, (Choloepus hoffmani). They don’t occur in the same high numbers as the Three-toed Sloth and also prefer to forage at night which makes them less likely to be seen by the casual observer. But one was located one afternoon high in the canopy by Matthias Klum, a world renowned Swedish wildlife documentary maker who works for National Geographic while walking the Zapatero Trail while on a recent trip to Bosque del Cabo.
Up in the canopy the Two-toed Sloth can easily be distinguished from its Three-toed cousin by the color of the fur. The former is very pale blond while the latter is a mid grey. Closer examination with the aid of binoculars will reveal the Hoffman’s has a longer face and lacks the markings which appear to give the Three-toed a permanent benign smile.
Both species consume leaf although the Two-toed has a much wider range of tree species from which it will feed. Also the Two-toed will supplement its diet with insects, chicks and eggs.
Hogging the Limelight
The area around Cabo Matapalo is home to several herds of Collared Peccary, (Tayassu tajacu). Although only distantly related to pigs they do look for all intents and purposes like small wild boar. Many of the visitors from the Southern United States are more familiar with them as Javelinas.
Just as with the sloths there is a second species of peccary that can be seen but only very occasionally. The White-lipped Peccary, (Tayassu pecari), is much larger than its collared cousin and prefers more pristine conditions. They tend to stay within the confines of Corcovado National Park but once in a while a migration will occur and a group will make their way along the Pacific coastline. Last week there was a small herd of about 16 individuals that passed by and stayed at Bosque del Cabo for the duration of a few days.
Both species of peccary are essentially herbivores and will take fallen fruits, dig up tubers and browse on leaves. The Collared Peccaries exist in smaller herds, which in this area number around 25, while the White-lipped Peccaries can be found in herds of 300. The Collared Peccary as the name suggests has a white ring around the body in the area of the shoulders. The White-lipped Peccary as the name equally suggests has the fur around the mouth area colored white. The White-lipped Peccary is also much larger and with long shaggy hair.
The presence of the White-lipped Peccary is hard to mistake. As they move through the undergrowth they continually huff and puff while at the same time clack their teeth. They also have a very powerful odor that is not pleasant to the nose of human observers. The herd passing through Bosque arrived overnight and then several days later disappeared as quickly as they had come.
Taking over the Airwaves
From January through to March the daily soaring temperatures and bright sunlight stimulate a constant high pitched white noise. This is cicada season. The cicadas in this area have a two year life cycle but that is staggered so that there is an annual emergence of cicada adults at this time of year.
Cicadas live most of their life in the nymphal stage below the ground where they feed by tapping into the vascular system of the roots and imbibing the sap. They progressively grow through a series of moults until after two years they are ready to emerge. The final nymphal stage emerges from the ground one night and climbs the nearest available tree or sapling. Within several hours the exoskeleton splits down the back and the new adult pulls itself out of the old skin. This is the winged, reproductive dispersal stage in the insects’ life history.
The newly emerged and fully winged adults fly to the top of the trees. The next morning as the sun rises and the temperatures climb then the calling begins. The males have two sound producing organs on the underside of the abdomen called tympani. Each one is like a tightly drawn drum skin. The increasing temperature throughout the morning enable the cicadas to vibrate the muscles connected to the tympani more rapidly which in turn vibrate the drum skins more rapidly resulting in a the volume and pitch of the sound they create to increase. Conversely should the clouds traverse the sky and obscure the sun then the temperatures drop and the pitch lowers and the sound softens. If the clouds persist then the calling may cease completely. Once they clear and the sun shines afresh the sound will rapidly rise to a crescendo one more time.
The female is attracted to the sound of the calling male and lands beside him. She does not call except by way of an almost inaudible clicking sound. They pair up and mate. The female lays her eggs in the bark of a tree. When the eggs hatch and the larvae emerge they fall to the ground where they quickly burrow beneath the surface to tap into the tree roots and feed on the plant sap. There they will spend the next two years before emerging and starting a new generation of cicadas.
From the Same Old Record to A New Record
After sixteen years of monitoring butterfly populations at Bosque del Cabo it is always a thrill when a new species not recorded for the lodge turns up. Recently I had the good fortune to have a new species to add to the list. It was encountered during the course of my weekly butterfly count.
It was spotted flying close the forest edge quite low down. I saw it alight under a leaf about 8 feet off the ground. Unfortunately the angle at which the leaf was suspended and the proximity of the other leaves meant that the butterfly was not presented in the best way to photograph. I did manage to get enough information to make an identification though. It turned out to be one of the metalmarks, Family: Riodinidae, this individual being of the species Thisbe lycorias. It is by no means a rare butterfly and in fact is widespread throughout the country. But nonetheless it was not a species I had seen before.
Philip Davison is a biologist, writer and photographer based in Costa Rica
Tuesday 2nd February 2016
Senna to Sleep
Over the past few weeks many of the trees have started to flower. The increasingly dry conditions stimulate blooming at this time of the year but because most of the floors are 100 foot up in the forest canopy then the only time the visitor has to see them is when flying over the forest or when the spent blooms fall to the ground and lie littering the forest floor amongst the dry leaves. However there are some smaller trees, shrubs and herbaceous plants that grow beneath the canopy or in more open conditions. Here you can get to see the floral display at a closer proximity.
One of those small trees generally found growing along sunny paths and roads is the Saragundi, (Senna reticulata). Its bright yellow flowers tinged with a hint of orange stand upright like fat golden candles giving the whole of the tree crown an overall fiery glow against the green background of the forest or azure blue of the sky. Stand beneath the tree and you will hear the constant buzz of bees attracted by its flowery display as they come to take nectar and pollen.
Despite its showy appearance Saragundi is not a welcome part of the native flora as far as farmers are concerned. It is a rapidly growing weedy tree that will quickly invade and take over open areas such as pasture land and nor is it easy to eradicate. It is little wonder that the local gardening team around here hates them with a vengeance and cut them down as soon as they germinate.
Should you see a Saragundi later in the day, more towards dusk, you will notice that the leaves start to droop and the plant goes to “sleep.” This is a feature common to many plants in the Fabacaea family, (legumes), and it is known as a nastic response. The base of each leaflet has a fleshy elbow called a pulvinus. During the course of the day the rhythmic flow of potassium ions causes water to either enter or exit the cells of the pulvinus. In the morning the large water holding cells become full of water making the pulvinus turgid which holds the leaflet out straight. At dusk water exits the cells making the pulvinus flacid and so the leaflet folds down appearing as if to go to sleep. It is not known what evolutionary benefit this nyctinasty conveys on the plant but it most certainly looks like some of the forest trees are dozing off for the evening.
A Rod of Gold
Growing along the currently dusty roadsides or lining the forest edge abutting the gardens are weedy long-stemmed plants that have a crown of yellow flowers atop. These are the Jackass Bitters, (Nuerolaena lobata). It belongs to the Aster family which includes the daisies and dandelions. It is one of the most species rich families of plants on the planet rivaled only by that of the orchids.
The flowers heads are composites; each individual head is a group of flowers, the greater display of many flowers together provide a more attractive visual target to potential pollinators.
There is a lot of folk medicine currently based on the supposed curative properties of Jackass Bitters but none that has any scientific backing. However its anti diabetic qualities are being scrutinized in a laboratory situation with regards to its ability to exert some control over blood sugar levels.
Canna Look at Your Lily
Tucked under the shady conditions beneath the taller vegetation where the garden meets the forest edge are a low growing plant with yellow flowers. These are the Canna Lilies, (Canna x generalis). It is mostly a hybridized form cultivated to bring a splash of color to leafy green flower borders. It is not obvious from which natural species of Canna that this variety has been hybridized but it is possible that it may be a Neotropical native Indian Shot, (Canna indica). You will seeing this variety growing freely in many garden situations around the country.
Going Bats for Garlic
Going for a walk through the forest this time of year may certainly cause a stimulation of your olfactory senses. There are many scents and odors that seem vaguely familiar but you cannot quite put bring to mind what it is simply because it out of context. Currently walking through the forest there are areas where you experience the definite smell of chives, or is it onions, no wait a minute it is garlic. What would garlic be doing growing in a tropical rain forest situation?
Here and there along the forest trail there are patches of yellow flowers littering the forest floor en masse. At this point the aroma of garlic is very strong. The flowers lie for some distance concentrically around the base of a large tree which given its appearance looks more like a tree from higher temperate forests. The bark is rough and deeply fissured, closely resembling an Oak Tree than a smooth bark tropical tree. This is the Ajo or Garlic Tree, (Caryocar costaricense), so named because its flowers give off a scent reminiscent of garlic.
There is very little wind in the Pacific lowland forests of Costa Rica so the plants have to rely on animal agents for pollination and seed dispersal. Bats are very important pollinators and seed dispersers but bats prefer musky smells rather that sweet smells which is why there are some very strange odors in the forest. It is the scent of garlic that attracts the bats in so the Garlic Tree is a bat pollinated tree.
Seeing Things in a Different Light
On the hot sunny days of the dry season many butterflies can be seen flying around the garden areas. There are several species that are noticeable due to their striking yellow coloration. These could be the “butter” flies. These are the sulphurs and they are not easy to tell apart species wise unless you have them in the hand.
Sulphur butterflies belong in the Subfamily: Coliadinae of the family: Pieridae. To the human eye the butterflies all have yellow coloration to a greater or lesser extent. Some may appear to be more creamy-yellow, others lemon yellow and yet others orangey-yellow but without exception – yellow, hence the name sulphur. But that is not how they look to other butterflies.
Butterflies, unlike humans see light at the ultraviolet wavelength of the electromagnetic spectrum. The dorsal surface of the male sulphurs wings are colored with a yellow pigment. This re-enforces a reflective ultra violet component that covers most of the dorsal wing surface and appears to sexually attractive to females which only have a small amount of ultra violet reflectance on their wings in comparison. The ultra violet patterning is used by the males in courtship displays. To human eyes the butterfly appears as a dancing honey colored piece of confetti. The females however see something different. Larger males with bright reflective radiance appear to be more attractive to larger females. In the world of the sulphurs flashy show offs get the girls.
Philip Davison is a biologist, writer and photographer based in Costa Rica.
Weather January 2016
Max Temp 40.0ºC (106ºF) Max Low Temp 25.1ºC (77ºF)
Min Temp 34.5ºC (94ºF) Min Low Temp 21.5ºC (71ºF)
Average High Temp 39.3ºC (103ºF) Average Low Temp 24.1ºC (76ºF)
Total Rainfall 42.7mm (1.68ins)
Animal Sightings January 2016
Greater White-lined Bat
Western Red Bat
White-throated Capuchin Monkey
Central American Squirrel Monkey
Mantled Howler Monkey
Central American Spider Monkey
Alfaro’s Pygmy Squirrel
Central American Agouti
Tome’s Spiny Rat
Striped Hog-nosed Skunk
Bare-throated Tiger Heron
Golfo Dulce Anole
Mediterranean House Gecko
Central American Smooth Gecko
Central American Whiptail
Barred Forest Racer
Green Parrot Snake
Black and Green Poison Arrow Frog
Golfo Dulce Poison Arrow Frog
Fitzinger’s Rain Frog
Stejneger’s Dirt Frog
Red-eyed Green Tree Frog
Savage’s Thin-fingered Frog
Philip Davison is a biologist, writer and photographer based in Costa Rica.
Thursday 28th January 2016
Stay Behind the Barrier
Black and yellow is the most visible color combination that exists. It follows that any creature sporting patterns in this visually obvious blend might not be trying to conceal itself. Bees, wasps and hornets are generally striped in yellow and black. Many poisonous spiders, butterflies and caterpillars are decked out in the same fashion. If they are not trying to hide then they are making themselves obvious, for whatever reason they are telling you to stay away. This strikingly acute combination of color is known as aposematic coloration or warning coloration. Humans use it too in the form of black and yellow striped tape to keep people from getting too close to a dangerous situation.
In the area of Matapalo these colors can be frequently seen and encountered throughout the forest. Flying along the forest rides and around the nectar giving bush Lantana camara in gardens are the brightly colored Heliconiids or longwinged butterflies. One of the most common of these is Heliconius sapho, its yellow banded velvet black wings beating slowly interspersed between periods of short glides as it makes its way down the trails. This aesthetic beauty is telling potential predators one thing – “STAY AWAY”.
The butterfly is unpalatable and what makes it unpalatable is the fact that it is packed with cyanide. Having a toxic defense against predation serves no purpose if the predator does not know about it. Eating one of these butterflies would result in the death of the butterfly and the creature eating it. The predators learn through experience. Once a predator, whether it be a bird or a lizard, catching and trying to feed on one of these butterflies will experience a foul taste caused by the cyanide. It spits it out and it does not take too long before the black and yellow coloration is associated with something so wholly unpleasant that anything dressed in the same colors will be avoided with a passion.
Leaf it Alone
It is not just adult Lepidoptera that use toxic defenses; many caterpillars are prone to do the same. Frangipani, (Plumeria rubra), despite being thought of as a Hawaiian plant whose flowers are used to make the leis to put around the necks of tourists, is actually native to Central America. It is the national plant of Nicaragua.
Frangipani continually flowers throughout twelve months of the year. As the sun sets the pale white blossoms give off a heavenly scented sweet perfume which drifts into the night, the aroma of which attracts night-flying hawk moths. The moths are attracted with the promise of a nectar rich feed. But nectar is energy expensive for the plant to produce so the plant cheats the moth; it reneges on the promise and produces no nectar at all. The duped hawk moth searches in vain but to no avail, the long proboscis probes into one flower after another and becomes covered in pollen. Flying from flower to flower it transfers the pollen and pollinates the plant. The moth having thus been enticed subsequently receives no reward for its labors.
There are moths that unwittingly have their revenge, the Frangipani Hawk Moth (Pseudosphinx tetrio). The eggs of this moth are laid on the undersides of the Frangipani leaves. Upon hatching the caterpillars are very small, only 10 – 15 mm. They won’t stay that way for long. After consuming their own egg shell they set about consuming the leaves with gusto. The caterpillar is a committed eating machine; it turns plant tissue into animal tissue at an incredible speed. They can almost be seen to grow day by day.
The last part of the leaf to be eaten is the stalk. If damaged the stalk leaks a stiff white liquid rich in alkaloids. The alkaloids are very toxic and would normally deter anything from consuming the leaf. The Frangipani Hawk Moth caterpillars store the alkaloids in their bodies making them in turn highly toxic. Once more that information needs to be relayed to any potential predator to save both parties from harm. The vividly black and yellow hoops with a flash of bright red head, tail and legs should serve the purpose very well. It appears to do so as these caterpillars feed in full view both day and night on the very naked limbs of the Frangipani.
Within little more than a week the plant will be denuded of leaves and the caterpillars will have increased to a very stout 60 – 70 mm. Should more plant tissue be needed to complete the larval stage before pupation then the caterpillars set about consuming the rubbery branches of the tree. One night, as if by magic, all the caterpillars will have disappeared, retiring to some secluded nook or cranny to pupate before emerging in the future as a relatively drab moth which will mate and start the process over again. Although the Frangipani may look a little forlorn in its leaf denuded state, it really doesn’t take long for it to produce fresh growth, in fact quite often on parts of the plant as the caterpillars are still feeding.
Beware a Colorful Meal
Spiders might not be that easy to find but once you start to look they are everywhere. In common with many other forms of life, the species richness and diversity of spiders is huge. More obvious than most are the orb weaving spiders, the webs of some species traversing large expanses between trees. However there are many smaller spiders with consequently smaller webs. One of the more distinctive of these is the Arrow-bodied or Spiny-bodied Spider, (Micrathena sexspinosa). Either name is appropriate and speaks for itself.
The body of the spider has an array of spines and thorns which in itself should be enough to discourage any potential predator. But sometimes physical defenses can be overcome. The spider has invested in a second insurance policy – a foul-tasting chemical defense. As with the above butterflies and caterpillars there is no point having that means by which to avoid predation if the predator is oblivious to its existence. So once again aposematic coloration comes into play, the spider is dressed in a black and yellow checkered pattern.
Any naive bird or lizard that ignores the warning signs and tries to eat the spider will end up with the spider jammed in its bill or mouth by way of the spines and thorns. All the while the spider issues from its skin a nasty tasting secretion that the unfortunate predator has to endure while trying to remove the spider from its bill or mouth. Once the cause of the vile experience has been eliminated then the bird or lizard will probably never attempt to eat anything black and yellow again.
Tiny Timid Tigers
For the last example of black and yellow aposematic coloration we turn to the hymenoptera, more specifically the ants. Ants like spiders may not at first be as obvious as mammals, birds and butterflies but take the time to look at little more closely and they most certainly are there. Leaf-cutter Ants are hard to miss, their long winding ribbons of green cut leaf fragments running like verdant rivers across the forest floor. Army Ants likewise when in a foraging frenzy move in fronts upto sixty feet across appearing as an almost large black plastic sheet being pulled across the forest floor, its intent being the slaughter and butchering of all small forms of life unfortunate enough to not be able to escape from its path. Noisy excited attendant birds and the hum of parasitic flies usually herald its approach.
But rather than these mass movements there are many other ants that occur in smaller numbers. Seen walking down tree trunks, along branches and roots in small lines like kids playing follow the leader are distinctive black ants with golden bands, the Tiger Ants, (Camponotus seriseivestris).
Tiger Ants are closely related to the Carpenter Ants and share the same life history as general foragers taking nectar, seeds and fruit from plants. They attend aphids and certain Lycaenid caterpillars for honeydew as well as taking small creatures either dead or alive. They live in colonies in hollows within dead or living trees but in much smaller numbers than Leaf-cutter or Army Ant colonies.
The name Tiger Ant conjures up visions a seriously ferocious adversary capable of doing limitless damage to any unsuspecting tourist that accidently puts his hand upon them. In actual fact they are harmless, most certainly to humans, the name referring to the coloration rather than their nature. They do however have a means of defense if disturbed. The aggravated ant will turn its abdomen between its legs so the rear end is facing forwards and then it will shoot a jet of formic acid towards its aggressor. Many ants indulging in the same defensive strategy will generally deter the cause of its ire to retreat to a safe distance.
Philip Davison is a biologist, writer and photographer based in Costa Rica.
Monday 25th January 2016
A Sinister New World Emerges
Once the sun sinks low on the horizon and the light levels fall to dusk then the daytime animals return to the safety of their nightly abodes. There is not much twilight this close to the equator, the sun seems to fall from the sky and before you know it darkness has descended and the world around you takes on a very different atmosphere. The calls of birds ceased some hours ago. Those cicadas whose constant high pitched hiss has permeated throughout the hot sunlit day have now gone quiet. Even the sundown cicadas, the white noise of which replaces their daytime cousins, have called to a crescendo the fortississimo now having fallen silent too. The blackness that was the green lawn starts to flicker here and there with small green flashes of light as the male fireflies emerge, the twinkling stimulating a response from the females which live higher in the vegetation. In the background a Spectacled Owl, (Pulsatrix perspicillatus), calls sounding for all the world like a distant muffled laugh. Not too far away a ground roosting night hawk, the Common Paureque, (Nyctidromus albicollis), calls with a series of plaintive whistles. The night shift has begun.
All the Better to See You
From somewhere hidden for the day deep in the depths of the undergrowth nocturnal snakes emerge. There is one with a body long and pencil thin that supports a head seemingly too large and out of scale with the other dimensions. It has large eyes, very large eyes, all the better for seeing its prey. The snout is short and the eyes are directed forwards giving it some perspective. The long slender body is triangular in section which reinforces the skeletal strength of what is little more than a muscular tube. This is the Brown Blunt-headed Snake, (Imantodes cenchoa).
The slightness of the serpent allows it to move unnoticed through the branches and leaves which make no movement in its passing. Like an angel of death it seeks a victim. The tongue flicks in and out constantly sampling the air until it picks up on an odor measured in quantities at the molecular level. The scent plume leads the snake to its source and consequently its prey, a sleeping lizard.
Lying in Peril
This lizard is a Golfo Dulce Anolis, (Anolis polylepis). It has been active during the day waiting head down on a leaf in low lying vegetation for hapless insects to wander by. It jumps from its ambush position, grabs the meal and consumes it in quick time. Bouts of feeding maybe punctuated with territorial disputes of chasing interloping males from its territory or perhaps courting a passing female. With the day’s activities at an end it retires to what would normally be the relative safety of a leaf tip to sleep for the night. Any predator approaching on the leaf would cause vibration which becomes amplified along the length of the leaf thereby warning the sleeping lizard which awakens to the imminent danger. It jumps off and disappears into the leaf litter below.
Tonight however the lizards sleeping position is not so safe as doom is approaching from a different direction. The Brown Blunt-headed Snake is not on the same leaf. Its search has led it to a position on a plant in close proximity. That long strong sinuous body reaches out across the gap. It has already identified where its meal lies. The lizard is oblivious to its presence. The snake’s body draws into a series of s-shaped loops and then with lightning speed and precision the strike is made. The lizard knew nothing of its final moment on earth, dispatched and eaten like the insects that met their fate in a similar way earlier in the day.
Upping the Ante
Not all lizards sleep at night though. There are nocturnal lizards, the most common and noteworthy of which are geckoes. Around the Osa Peninsula there is a very common gecko that can be found in all buildings and on the trunks of garden trees. It is a visitor that became naturalized, the Mediterranean House Gecko, (Hemidactylus frenatus), hitching a ride from Southern Europe courtesy of human transport and wherever conditions were suitable then there it settled, not just here but in tropical conditions everywhere. They are familiar to most people as those small creatures hanging around by house lights to catch the insects attracted in by the incandescent glow.
Asleep or not the gecko is still a meal that does not escape the attention of the Brown Blunt-headed Snake. With a similar stealthy approach it closes in on a gecko which remains perched head down on a tree trunk waiting for insects to land. But this hunter is about to become the hunted, the difference being this one is wide awake and alert to the danger
The snake slithers into position, the tongue confirms the gecko’s presence, the eyes focus forward and the scene is set. The snake strikes out, the jaws agape but the gecko’s reaction is rapid and it moves just in time. The snake does not miss its target but rather than hitting the body the jaws close and the teeth sink into the tail. Here the gecko has another defense, the tail breaks and the snake is left with little more than a wriggling piece of tail section, not much of a meal but better than nothing.
Meanwhile the gecko has scuttled off post haste up the tree trunk, the missing tail section being little more than a minor inconvenience. The most important thing is that it is still alive. That missing part of the tail will regenerate over the coming months and apart from the fact that it will be of a slightly duller color than the original there will be nothing else to show for the encounter.
Philip Davison is a biologist, writer and photographer based in Costa Rica.
Monday 18th January 2016
Spiders are an amazingly diverse group of animals, the eighth most diverse group of animals of the planet in actual fact. It doesn’t take long while poking around in the undergrowth to come across a spider. Some build webs and some don’t but they can all spin silk, the orb weavers having the ability to spin upto seven different types of silk. The non-orb weavers tend to be ambush predators, remaining motionless in a strategic location where potential prey may wander innocently by unaware of the imminent life threatening danger. The ambush position could be on the side of a wall, atop a leaf or sitting on a flower head.
This Wandering Spider, (Cupiennius sp), was sitting perfectly still on a blank white wall at night. As many spiders are nocturnal predators the eyes play a lesser part in the identification and capture of a meal but that does not imply the spider is without the means by which to locate the exact location of its prey. The body, which at first sight looks smooth, upon closer examination can be seen to be covered in hairs of different lengths. These hairs form part of a battery of sensitive sense organs responsive to touch, vibration and moving eddies of air currents that allow the spider to detect a passing meal in the darkness.
The majority of hairs covering the body, which give most people the heebie-jeebies with regards to spiders, are tactile and touch sensitive, the stimulus of which will cause the spider to attack or run away. Between the shorter hairs, particularly on the legs are long fine hairs called trichobothria. These are super sensitive to the slightest movement in air currents which can be a giveaway for any larger creature passing by which could make a nice meal. The Wandering Spiders can even detect insects such as moths flying overhead which they jump and grab straight out of the air.
For those more stealthy prey items whose movements are too slow to disturb the air, they cannot avoid causing small vibrations of the substrate and the spiders are attuned to this also. Around the body but more particularly around the leg joints are slit sense organs which allow the spider to detect any vibrations moving through the substrate upon which it is placed.
Whereas the Wandering Spiders rely on their tactile senses at night during the day there are spiders that actively hunt down their prey visually. The Jumping Spiders prefer to hunt in full sun. The most obvious feature are the large anterior eyes with which they can locate and subsequently stalk their victims. They stealthily approach to the point where the potential meal is within striking distance. The spider braces itself and then pounce. The fangs are embedded upon impact, pumping venom into the victim which is held in a death grip by the front pair of legs.
Hunting the Hunters
The spiders may be highly adapted carnivores with specialized hunting techniques but they too in turn have predators specialized to catch and eat them. Not the least of these are the giant Helicopter Damselflies, (Megaloprepus caerulatus), the largest damselflies on the planet. They can be seen flying along the sunlit trails through the forest. The peculiar motion of the blue/black tipped wings gives the impression of rotating helicopter blades. What may at first seem like a somewhat erratic flight pattern actually has design. The more astute observer will notice that they have the ability to fly vertically up and down as well as horizontally in and out. But what are they seeking? The large eyes and acute vision are scanning spider webs in front of which they momentarily hover scanning for the silken structures builder. Once located the spider is grabbed in the legs of the damselfly which goes into reverse gear before biting off the spiders head and legs to finally gorge itself on the soft body parts.
The damselflies can be recognized when they alight by the habit of folding the wings together over the body. Their cousins, the dragonflies keep the wings held out to the sides when at rest. During the day it is not too often that they do rest. Each individual has a perch from which it frequently takes off to investigate any passing creature that might make a meal or another dragonfly that might prove to be a mate or another dragonfly that might be a rival for that meal or mate. They make aerial sorties swooping at speed, hovering in place and if unmoved to action return to the perch for a short while before they are off again on another sortie.
They differ from the more delicate damselflies not only by how they hold their wings but also in the structural placement of the eyes. Damselflies have two large compound eyes widely separated on either side of the head. Dragonflies have two large compound eyes that meet together for a greater or lesser part of their margins on top of the head. However no matter where the eyes are placed they allow for excellent diurnal vision which combined with the unsurpassed aerobatic proficiency make these some of the masterful airborne hunters.
As we move into the dry season the hot and parched conditions stimulate many of the plants into flowering. This is most certainly true of the orchids. There are two orchids that can be seen blooming at the moment in the area. One is a non native terrestrial orchid, the Bamboo Orchid and the other is a native epiphytic orchid.
The Bamboo Orchid is a native of South East Asia but is planted in many parts of Costa Rica as a beautiful ornamental edging plant. Bamboo refers to the long erect stalk that resembles that a of a bamboo grass. The attractive purple flowers appear throughout the year giving a nonstop display of color for the back of a flower border.
The majority of orchid species in Costa Rica are epiphytic, that is they grow on the outside of trees without harming them. Generally to see orchids you need to be at the top of the canopy, 88% of Costa Rica’s 1400 orchid species are to be found there. Many of the orchids flower from December into January but some may be seen flowering at any time of the year. This particular specimen was found growing close to the ground near the base of a large tree. Due to the diversity of genera and species the identification of orchids, like so many tropical plant and animal taxa, is the realm of specialists. For most visitors it is enough to see and enjoy the exotic blooms should you be lucky to encounter them.
Philip Davison is a biologist, writer and photographer based in Costa Rica.
THURSDAY 14th JANUARY
Blue and Brown
As the wet season fades into memory and the dry season progresses then the number of butterflies increases. Week by week as the weather becomes warmer and drier you will start to see more and more species of butterflies and not only that but also an increase in the number of individuals. The best place to observe the most colorful of these constantly fluttering confetti-like insects is in the open areas particularly around the nectar plants that they favor which in this area happen to be the orange/yellow flowers of Lantana camara. Here bright poster colored, slow flying heliconiids painted in yellow, orange and red are conspicuously flitting from sunlit flower head to flower head. The casual observer will not fail to be impressed by the constant swirling to and fro of so many different species. Flying overhead but not landing are the sulphurs, butterflies dressed, as the name suggests, in vibrant yellows and creams. They exhibit ultra violet markings, invisible to us, but seen by other butterflies or by humans with a U.V. filter.
Down by your feet, visiting and taking nectar from the flowers of low growing herbaceous plants, are butterflies so small as to be barely discernible. Concentrate your attention to the level of the grass and there will be revealed a motion of tiny flicking blue wings, butterflies smaller than a fingernail. These are some of the Lycaenids, the Cenaurus Blue, (Hemiargus hanno), and the Eastern Tailed Blue, (Cupido comyntas). Their delicate form and intricately patterned wings decorated with dark spots, pale dashes and splashes of red can only really be appreciated if you lie down at their level and watch them close up.
Moving into the forest beneath the umbrella of the canopy which casts the forest floor into shade a whole other group of ground hugging butterflies can be seen, but once again only with patience and a sharp eye. Most of these butterflies disappear as soon as they alight amongst the dead leaves or on the textured bark of trees. The satyrs have a ground color in shades of grey and tan. Overlying this are streaks of browns in ochres and chestnut. They look like the leaves amongst which they settle.
There are several species of butterfly in the same subfamily as the brilliant Blue Morphos that do not have the bright blue coloration. One of them, the White-signed Morphet, (Antirrhea philoctetes), looks more like a satyr than a morpho. It is a beautiful tan and chocolate brown with darker dashes, black dots and a white stripe across the underside of the fore and hind wings. It also sports a distinct eyespot. Just as the earthy colored satyrs, the White-signed Morphet never flutters more than a few inches above the ground. When it lands it remains motionless blending in perfectly with the background.
Another butterfly that remains unmoving on the side of tree trunks is the Owl Butterfly. Having been unnoticed the close proximity of a walker on the trail may cause the butterfly to take to the air. But not for long as it quickly settles head up on the trunk of another tree. If you approach slowly you can see the intricate patterning of browns, tans, creams and yellow overlain with wavy black bands.
The most distinctive and distinguishing feature is the large eyespot on the underside of the hind wing that gives the butterfly its name – Owl. The large dark bordered ring with a central pupil, along with white spots that mimic a catch light look just like an eye. The illusion is deliberate. This is a bullseye, a target for potential predators. A bird, a lizard or a mouse will attack in the area of the eye because normally lying behind the eye is the major part of the central nervous system – the brain. Wipe out the brain and the prey is killed instantly. In the case of the butterfly the target is placed on a non vital area of the hind wing that the butterfly can afford to lose without it hindering its ability to fly. All the predator disappointedly ends up with is a tatty piece of wing membrane. As can be seen in the photo the Gold-edged Giant Owl, (Caligo atreus), the hind wing shows evidence of a previous attack.
Everywhere and Nowhere
A common question asked by visitors to the tropical forests is “Where are all the mushrooms?” The fungi are most certainly here, the extensive mycelia of which permeate the soil reaching into and spreading throughout any dead organism whether it be animal or vegetable aiding in that process of rapid decay and decomposition. But in these warm wet forests conditions are ideal all year round for the production of those familiar reproductive spore producing bodies – the mushrooms and toadstools. In higher latitudes the almost overnight appearance of such a rich variety of fungal fruiting bodies is a visual treat for hikers in the forests and mountains. But it is an all at once autumnal phenomenon. Within a month or so the event has ended. Here if you look carefully there will be mushrooms but not in such profusion or rich abundance.
This was a group of agaricales that were found growing on decomposing lawn mowings which had been discarded at the forest edge. They were in various stages of fruiting from small and unopened to fully extended caps. Actually the mushroom will grown very quickly overnight, open, shed millions of spores into the air and can have gone within 24 hours. There are many animals that enjoy taking advantage of this sudden appearance of a tasty meal with flies laying eggs from which the larvae emerge very quickly to feed and develop. Mice and squirrels enjoy the fungal feast as long as they are not poisonous, something humans have to be very wary of as there are some deadly toadstools out there. Better to appreciate and enjoy the texture, form and function of these interesting ephemeral appearances than risk sampling the terminal flavor of an exotic final meal.
Jumping to an Identification
Crickets, katydids and grasshoppers can be found in all tropical terrestrial ecosystems during both day and nighttime hours. They might not be the easiest things to see but hearing them is unavoidable. Although they all belong to the order: Orthoptera there are differences between the three groups. Most familiar grasshoppers are brown or green and have short stubby antennae. Grasshoppers make raspy sounds known as stridulation by rubbing the femur of the hind leg against either the front or hind wing. Katydids are an elegant group consisting of many forms and colors. Some not only have the green coloration of vegetation but have evolved remarkable mimicry with the wings resembling the veins and patterning of leaves against which they are almost indistinguishable. Katydids, along with crickets, stridulate by rubbing the forewings together. Katydids tend to have more pleasant calls than the grasshoppers but are not as melodious and musical as the crickets. Both katydids and crickets tend to have long filamentous antennae. Grig is an older English term for the jumping insects of the order: Orthoptera but these days generally refer to a separate family of katydids.
Philip Davison is a biologist, writer and photographer based in Costa Rica.