Wandering Spiders: Nocturnal Predators of The Rain Forest   2 comments


Philip Davison Nature Diaries. Bosque del Cabo Rain Forest Lodge.

 

Today I saw for the first time a Long-tailed Woodcreeper, (Deconychura longicauda).  It is not a common bird in the South Pacific region of Costa Rica, which is the same for a lot of the plant and animal life here.  In terms of biodiversity, there tend to be a lot of species but not many individuals of any one species.  There is a saying, “Common trees are rare, rare trees are common” which can be applied across the board.  Nonetheless for a biologist out in the field every day, which is where I have spent the majority of my working life, it is still a thrill to see something new.  And to that effect, I am, therefore, thrilled on an almost daily basis; there is always something new to see.

First time visitors to the tropics will be captivated by many new sightings, almost everything will be a first time experience, plants and animals only ever seen in books or on T.V.  For a resident in these forests though, the daily viewing of monkeys, coatis, agoutis, macaws, and toucans can sometimes render you complacent of their presence.  It is not until something like a Long-tailed Woodcreeper appears that makes me once again contemplate the marvel of it all, nature, its diversity and all the complex interactions that exist within the system.  Take any one element out of the system and, although it may not be obvious, the system will be diminished.

Along with the woodcreeper, this week I have seen for the first time Turquoise Cotingas, (Cotinga ridgwayi) and White-lined Tanagers, (Tachyphonus rufus).  For only the fourth time in ten years, I saw the Eyelash Viper, (Bothriechis schlegelii).  But, my main interest is with the butterflies.  I have been fascinated by butterflies since the age of three.  I don’t know what it was that ever first captivated me, but whatever it was has had a very strong hold on both my imagination and natural curiosity.

On the grounds of Bosque del Cabo, over a ten year period I have inventoried 400 species of butterfly, all at ground level.  Most butterflies live at the level of the tree tops, so imagine how many more species I could add to that list if I could monitor in the canopy.  The species inventory for the nearby Corcovado National Park is 220 species.  Once in a while I will get one, two or perhaps three new species turn up in a week.  That puts a spring in my step and a smile on my face.  It amuses me when I am leading a guided tour through the forest and I stop everyone in their tracks, then move slowly towards something that has caught my eye.  The onlookers, paused with baited breath wait for me to signal for them to come forward and see the elusive and hidden form of some large cat, only to be shown a small, almost imperceptible, but never before seen by me,  species of skipper or hairstreak.  Each to their own, but that sighting will certainly have made my day.

Wandering Around At Night With Spiders

 

Wandering spiders, (Cupiennius spp), are nocturnal spiders.  As darkness descends, they emerge from their daytime hiding places and set up their position for the night.  They prefer plants with broader leaves and some form of cavity, perhaps a hollow stem, which they use as a daytime refuge away from the drying sun and wind.  They do not build webs, they are ambush predators.  The Wandering Spiders are finely tuned killing machines; they have vibration detectors and sensitive hairs on the legs that alert them to the presence of prey in their vicinity, any cockroach or cricket that may pass by.  The vibration detectors sense the movement of its prey on the leaf surface.  The hairs on the legs are very sensitive to minuscule eddies in air currents close to the spider.  The unfortunate insect is unaware of the imminent danger, the spider remaining motionless until the last moment, the spider’s leg borne sensory apparatus giving precise information about the insect’s proximity.  When the prey comes within range, the spider moves with lightning quick speed, it pounces forward and grabs the prey with its front two legs which hold the unfortunate victim in a vice-like grip while it sinks its fangs, chelicerae, into the hapless individual.

Arachnida. Araneae. Ctenidae. Cupiennius coccineus. Osa Peninsula. Costa Rica.

Wandering Spider emerges just as the sun sets

After envenomation, the prey is held at legs length away from the spider to prevent it retaliating with a bite or sting of its own against its assailant.  It is held above the leaf surface so that it has nothing to struggle against in an attempt to wrest itself free.  The whole attack took less than 0.2 seconds.  The venom works quickly on the prey’s nervous system, paralysing it into a state of immobility and finally death.  In terms of energy expenditure, venom is very expensive for the spider to produce and generally nature does not waste energy.  If the prey is small enough and poses no threat to the spider, then it will simply be overpowered and killed without the spider resorting to its precious venom supplies in order to subdue it.

Wandering Spider. Felipe del Bosque.

This is the last thing a prey item will see – the head of its killer

Spiders do not have mouth parts capable of chewing, so digestive juices are pumped into the prey converting the insect’s tissue within its shell-like exoskeleton into a soup which the spider eventually proceeds to suck out. Some of the larger wandering spiders will feed on the smaller frogs by the pond and have even been seen jumping on and biting the snakes.  They also have the unnerving ability to jump and snatch flying moths straight out of the air.  There are no spiders or scorpions in Costa Rica capable of killing you, but wandering spiders can inflict a nasty bite which will result in a localised ulceration.  But if you keep you distance you can watch these intriguing creatures going about their business almost everywhere at night.

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

 

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Posted August 29, 2010 by felipedelbosque in Philip's Nature Diary

2 responses to “Wandering Spiders: Nocturnal Predators of The Rain Forest

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  1. Wonderful article. I also am a lover of butterflies. My mum instilled it in me and I have been busy keeping all the weeds from being cut down, which are the wildflowers the butterflies love. The tiny flowers bring tiny Butterflies. We have many of these wandering spiders around our home and I lived with a giant one for about 2 weeks. It finally left after I started examining it too closely. It actually started walking towards me threateningly then never returned from its next nights hunt.

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