Archive for the ‘Pteridophyte’ Tag

Phasmids: A Neotropical Walking Stick   2 comments


Wildlife, nature, fauna and flora of Costa Rica.

Sticking to the Twigs

There are some animals that live out in the open, right in front of your eyes, and yet you never see them.  That is because they don’t want to be seen.  Only when mistakenly they venture forth onto a background that reveals their presence will you have the opportunity to marvel at their disguises.  One such group of animals are the Phasmatodea, more commonly known as Walking Sticks or Stick Insects.

Last week I saw one that had made such an error.  It had left the vegetation where it lives perfectly concealed from view and had wandered onto the screen of my cabin.  There it stood out like a sore thumb.  Thankfully for the phasmid it was my eyes that saw it before those of any potential predator.  If removed the unfortunate creature and placed it back amongst some twigs from which I could take its picture but also from where it could make its way back into the obscurity of the vegetation.

Phamatodea: Walking stick in Costa Rican Rainforest

The long spindly legs and body of a Walking Stick make enable it to avoid the attention of predators

The body and legs of the walking stick are long and spindly.  They are either green or brown in color and quite often, as this one was, a mixture of the two.  The body and legs are grooved and have small thorns.  They resemble so perfectly a twig that, even when you are looking directly at them, they are imperceptible.  Some species have wings but not the one I was looking at.  They are vegetarian and tend to be host specific.  Walking sticks reach the zenith of their diversity in tropical forests such as these, of the 2,500 species identified so far, 30% live in the Neotropics.

As well as the perfectly camouflaged body form the phasmids use other means by which to complete the illusion.  This one, when disturbed, would rock back and forth as a twig being blown in a breeze.  Then it would freeze and hold the front legs as well as the long filamentous antennae out in front of its head to make to enhance its long twig-like form.

In and Out of the Rainbow

There has been a new wave of plant life that has come into bloom over the past week or so.  The cycle of change in the forest is such that throughout the year you are never short of something new to see or hear each time you venture out onto one of the trails.  As the flowers of certain species turn to fruit, then so do others come into bloom.  The flowers and fruit provide a continual annual transition of color and form.  You only have to keep your eyes open as you walk and you will be rewarded with a visual sensory feast.

Last week one of the most obvious additions to the floral display was the Recadito, (Palicourea guianensis) of the family: Rubiaceae.  The multi-clustered bright yellow flowers are borne on a vivid red stalk at the end of the branches.  They are visited a lot by butterflies, especially if found growing at the forest edge.  It is a small tree with large leaves and is reasonably common in wet habitat from Mexico to Bolivia.  There are 27 species of Palicourea to be found in Costa Rica, 3 of which occur on the Osa Peninsula.

Rubaceae of the Osa Peninsula, Costa Rica.

The distinctive floral display of Recadito, (Palicouria guianensis)

Another related plant, but much smaller and subtler is the Cafecito, (Psychotria capitata).  It too, belongs in the family: Rubiaceae but it is a very large genus, 115 of which live in Costa Rica, 40 of those on the Osa Peninsula.  They are not always easy to identify to species level.  This one, Psychotria capitata has small white flowers which when pollinated give rise to small purple berries.  At that point it resembles a rather swollen blackberry fruit.

Cafecito, (Psychotria capitata), Osa Peninsula, Costa Rica.

Delicate white flowers of the unobtrusive Cafecito, (Psychotria capitata)

Crosier for a Green Bishop

Ferns, or pteridophytes, are non-flowering vascular plants that most people who enjoy walking in the countryside will be familiar with.  You will not see fruits or seeds as ferns produce tiny dust-like spores produced in special spore cases on the underside of the leaves.  There are about 800 species of fern in Costa Rica but their form is so distinctive that they are not too difficult to recognize as such.  They are mostly low growing in shady areas of the forest but there are some that grow to a substantial size, the tree ferns.  These behemoths of the pteridophyte world, along with the cycads, were the dominant form of terrestrial vegetation before flowering plants evolved, and can be regarded as the “Food of the Dinosaurs”.

There are tree ferns found growing in these forests but they don’t reach the giant statures of those in other parts of the world.  Most of the ferns here are of the low growing type.  When a new leaf is produced it lies in the center of the plant, wound around itself like a green rope on a spool.  As the days pass it unfurls up and outward, revealing leaves that appear as an organic fractal, repeating the pattern on a smaller and ever smaller basis.  Eventually as the stalk has reached its maximum growth, the final part resembles a Bishop’s Crozier, which ultimately uncurls and the side-branching leaves and leaflets open out to reveal the familiar frond.

Pteridophytes of the Osa Peninsula, Costa Rica.

An unfurling fern frond

Mustachioed Murderer

Walking through the forest I entered a more open spot where the sun was lighting up a clearing.  I noticed something move very quickly on the forest floor.  It settled on the surface of a leaf.  I knew what it was but to begin with I was a little puzzled as it looked to possess four large eyes, so in my mind I was looking at one insect perched on top of another.  I bent down to take a closer look and I could now see my mistake.  There were most certainly two very large distinctive eyes but the dark markings contrasting with the yellow ground color of the thorax gave it the appearance of a second insect sitting on its back.  I could now also confirm my identification as that of a Robber Fly, family: Asilidae.

Robber flies are true flies of the order: Diptera and therefore only possess one pair of wings.  A distinctive feature of the robber flies is the cluster of hairs at the front of the head that give them a look of an Edwardian gentleman sporting a rather luxurious mustache.  This is known as a mystax, which is taken from the Greek word for mustache.

Why would a fly have a protective mustache of bristles protecting the front of the head?  The Robber Flies are accomplished predators and will hunt down any arthropod of a suitable size, not too small, not too large, that makes the unfortunate mistake of entering into the killer’s field of view.  The Robber Fly has large eyes and respond with speed to a potential meal.  It uses the stiletto-like piercing mouthparts to stab its victim and to inject a saliva which contains a deadly cocktail of neurotoxins and cell destroying enzymes which render the prey to a corpse being digested from within.  The fly then sucks out the pre-digested meal.  They have no hesitation in attacking wasps and ants which themselves are capable of inflicting a fatal bite or sting.  The mustache serves to protect the fly from such retribution.

Asilidae: Robber fly on the Osa Peninsula, Costa Rica.

Assassin with stilleto ; Robber fly with cockroach prey

Robber Flies prefer sunny gaps in the forest, which is exactly where I found this one.  They sit on a perch located low to the ground and wait for a meal to pass by.  Their reaction speed is so fast that in a blur of the eye they can snatch a flying insect out of the air.  You can see in the photograph that this one had just caught a tropical cockroach.  Don’t try to catch one in your hand as a stab from that proboscis is very painful.

There are about 7,500 species of Robber Fly distributed around the planet, preferring warmer areas that are arid or receive only seasonal rainfall.  They are not that hard to find, pick a sunny light gap and then you just have to sit and watch for that quick movement.

Philip Davison Is a Biologist, Writer and Photographer Based in Costa Rica