Archive for the ‘Asilidae’ 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

Advertisements

Diptera: The True Flies   1 comment


Wildlife, nature, fauna and flora of Costa Rica.

 

Photography is a very popular hobby, it has been since the invention of the first image recording apparatus started to replace portrait artists.  Initially it was beyond the scope of most people’s pockets and outside of professional realms was something of an elitist pastime.  But by the time I was growing up in the sixties many amateurs had at least moved on from a Box Brownie to a Kodak Instamatic.  Now the array of point and shoot pocket cameras is quite staggering, there is every type of model and specification to suit every level of expertise.

Many people have gone a step further and invested in a digital SLR featuring a range of interchangeable lenses allowing them to photograph in a wide variety of situations from landscapes, portraits and more specialist areas such as wildlife photography.  A sizable number of visitors to Costa Rica have spent no small sum of money on equipment to record for posterity the beauty of their surroundings and the plants and animals that thrill and delight them during their stay.  Some are more proficient than others and wildlife does not always co-operate with having its picture taken.  But given the technological development of today’s cameras it is hard not to take a good picture of whatever you aim the lens at.

For many it is a case of getting a picture of the bigger creatures such as mammals and birds, occasionally turning their attention to the more gaudily colored butterflies, pretty frogs or ever darting dragonflies.  For me though it has always been the small things.  I love photographing spiders, insects, frogs, lizards and snakes.  The majority of my work is macro photography; if it is more than six to nine inches from in front of the lens I generally won’t take a picture of it.

Everything has its own inherent aesthetic physical beauty; it’s just that until you take your time to get up close and personal you are probably not going to recognize that.  How many people would give a fly a second glance before swatting it to death?  But seen through a macro lens it takes on a different aspect, the insect almost has an expression.

Macro photography has its own set of challenging techniques, not the least of which is how to get so close to your subject.  Quite often slow, fluid movement is the essence of success, no fast, jerky moves or you will stand frustrated as that never before seen butterfly disappears.  Patience is a virtue macro photographer’s need in abundance.  If you have carefully composed your photograph perfectly in the frame and go to press the shutter, a leaf falls putting the subject to flight, just wait, it will probably come back.  When I am taking photographs of insects capable of flight, I approach them in a manner resembling some elderly Chinese gentleman doing Tai chi with a camera.

Light, you will probably need lots of light. Capturing the face of an insect at very small apertures allowing greater depth of field, means that little natural light will hit the sensor, more acutely so if you are shooting in deep forest or at night.  I normally carry with me five wireless flash units that allow me to create my own atmospheric lighting, again not easy to set this up if you are trying to capture the image of a flying insect.  But when you do get the shot, the one that reveals all the beauty hidden from the naked eye, it will give you so much satisfaction.  If you haven’t tried it, give it a go.  It is a challenge but one that is worth the result.

Flies Eyes

Insecta. Diptera. Osa Peninsula. Costa Rica. Felipe del Bosque

Stunning green eyes of unidentified Diperan sp

I have a fond affinity for flies having spent two years in the ancient oak woodlands of Epping Forest, England monitoring fly populations.  They are regarded by many as, at best, little more than pests, and at worst, winged dispersers of disease, misery, death and decay.  This assertion unfortunately is correct.  Many serious diseases on a global basis are spread by dipteran vectors.  Amongst a host of others, several diseases have had, and continue to exert, an important economic influence on countries, particularly in the tropics; malaria, dengue, yellow fever and sleeping sickness to name but a few.  Mosquitoes are one of the worlds most feared and hated of creatures, being responsible for the spread of major epidemics.  It is hard to believe that something so small could have such a devastating worldwide effect.

Visitors to Cabo Matapalo quite often comment on the lack of biting insects.  Matapalo is situated at the top of a hill so all the rain is runoff, there is no standing water in which they can breed.  Breezes from the ocean and the gulf constantly blow through the grounds.  And finally there are a phenomenal number of insectivorous bats flying at night.  These three factors combine to make it a very pleasant surprise that you are not being eaten alive by midges and mosquitoes.

Insecta. Diptera. Sarcophagidae. Osa Peninsula. Costa Rica. Felipe del Bosque.

Who would have thought a Flesh Fly, (Sarcophagidae sp), would have such beautiful eyes

Flies feed on liquids, all sorts of liquids, everything from nectar to blood.  They have highly developed mouthparts to aid in obtaining a meal.  Flies differ from most other flying insects in having only one pair of wings, the rear set of wings being reduced and modified into a pair of balancing organs called halteres.  The thorax of flies is much larger than other insects as it houses mega flight muscles that allow sustained and powerful flight.

But out of the countless thousands of fly species, not all of them are bad.  There are flies that act as important economic pollinators, there are flies that predate upon other flies.  Despite their terrible reputation, start to look a little more closely and you may be intrigued to find that they have bizarre and fascinating beauty all of their own.

Insecta. Diptera. Asilidae. Mallophora sp. Osa Peninsula. Costa Rica.

Heavily mustachioed face of a Robber Fly, (Mallophora sp)

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

%d bloggers like this: