Flying a Dangerous Flag   6 comments


Philip Davison. Costa Rica. Blog. Nature Diaries

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 Postman Butterfly. Heliconius sapho.

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.

Frangipani Hawkmoth. Pseudosphinx tetrio

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.

Spiny-bodied Spider. Micrathena sexspinosa.

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.

Tiger Ant. Camponotus sericeiventris

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.

 

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6 responses to “Flying a Dangerous Flag

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  1. Always fascinating, Phil! Thank you! Kathryn Kostka de Tanzi

  2. A great read! I’m visiting Bosque del Cabo at the end of Feb and can’t wait now.

  3. Hi again Philip, I’m looking forward to my upcoming visit in a week’s time. I was wondering if you ever run a light trap at Bosque del Cabo? I just ask as I frequently survey moths in the UK so thought I’d ask on the off-chance!

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