Posts Tagged ‘arthropods’

Spiders: The Ultimate Predator

Tuesday, November 20, 2012 posted by Bruce 11:36 PM

Thailand’s 8-legged arthropods

Lawn wolf spider in Huai Kha Khaeng Wildlife Sanctuary

It is said arachnophobia, or the fear of spiders is common among people around the world who have an inherent trepidation of these creepy crawlies. Just the thought of coming in contact with one is something most of us dread.

But there are few souls out there who love them and even keep spiders as pets. However, the vast majority of us tend to just stay out of their way. Some spiders can give a nasty bite although fatalities are rare.

Like all living things, spiders have to face life’s difficulties such as finding food and mates, producing offspring, and fending off danger. However, spiders are the ultimate predator, and have been on the planet for a very long time.

Ornamental spider female and smaller male in Lampang province

The ancestry and anatomy of spiders are different from those of insects. Spiders have eight legs not six, and their bodies are divided into two parts rather than three. Many people mistake spiders for bugs.

The family tree of spiders is as follows: Jumping spiders, the largest and most highly evolved family, with hunting spiders and web spinners making up the main group. Tarantulas and trap-door spiders and others in this group plus ‘six-eyed’ spiders make up modern-day spiders.

Spiders are an ancient group that first appeared during the Devonian period, almost 400 million years ago. By the Carboniferous period (300 mya) when insects were still relatively little developed, many highly evolved spiders already existed. These arthropods appeared about 100 million years before the first back-boned animals.

 

Green linx spider in Lampoon province

Scientists have identified some 43, 244 species around the world. More than 230 species have been recorded here in Thailand with many more to follow. There are just a few people researching spiders and hence, knowledge is bit limited.

Dr Patchanee Vichuitbhun and Prasit Wongprom working out of Kasetsart University in Bangkok are the country’s leading arachnologists. Some five other graduate students are also working on spiders.

Together with their eight-legged relatives, the scorpions, harestmen, mites and ticks, spiders form the class Arachinda. Spiders alone represent the order Araneae and are classified in a family tree that numbers three suborders and 111 families.

Bird-eating spider in Phu Khieo Wildlife Sanctuary

Spiders are found virtually everywhere: in the house, in the garden, in forests, in caves, and in most other terrestrial habitats throughout the world. A few species live under water and some even in the marine tidal zone. The only place with no spiders is Antarctica.

While the greatest diversity of species occurs in tropical rainforest, spiders are also very well represented in temperate woodland and grassland. Spiders thrive wherever there is rich vegetation and plenty of insects or other arthropods.

Thailand has plenty of big scary-looking spiders but only a few species will actually bite a human being. Luckily, deaths from spider bites are very rare-less than 3 per year across the whole world and these are generally a result of allergic reactions.

 

Decoy spider in Chiang Mai province

Although virtually all spiders possess venom, only a small number of species, probably fewer than a hundred in the world, have a sufficiently potent and effective bite to be of medical importance. Spiders use venom to quickly immobilize or kill their prey. It is also used in defense against animals, including man, but this is only a secondary purpose.

Thailand is home to very few spiders that are dangerous to people. However, the brown widow is the most venomous. Tarantulas and golden orb weavers attract notoriety more for their size than their bites. Monitor all spider bites carefully to avoid the development of secondary infections.

The spiders of medical importance in Asia include widow and cupboard spiders (also called brown house spiders or false widows (family Theridiidae) which venom contains neurotoxins. Though not especially venomous, a number of Asian tarantulas or bird-eating spiders can also be regarded as potentially dangerous.

 

Orb-web spider in Ankor Wat, Cambodia

In many countries around the world, the practice of keeping spiders as pets seems a bit on the extreme to most of us, especially if it is highly poisonous. A few years ago, a brown widow escaped from someone and it made front-page news in some newspapers here in Thailand.

A trip down to Chattuchak Market at the pet section can provide one with a spider. There are rows and rows of shops catering to anyone who wants one. Most species on display are tarantulas from South America but there are some Asian ones too.

The pet trade is alive and well here in a business as usual atmosphere. It seems most of these shops act with impunity and no matter how many raids the Department of National Parks makes, they just pop back up and carry on. It is really disheartening to see how these mafia-type groups continue to operate.

Orb-web spider in Chiang Mai province

 Most people are not aware the dangers of keeping a tarantula that will flick off barbed hairs when alarmed causing imbedded hairs in the eyes and hands of the pet owner. Eye surgeons might be able to remove some hairs from an eye but many are likely to remain causing a serious medical ailment.

Something else the public needs to worry about is the brown widow, an invasive species from North America related to the very famous and notorious black widow. The brown species is now confirmed in 20 provinces in Thailand, and probably came over on ships. The bite from one of these is extremely painful but there have been no fatalities here yet. There is no anti-venom for this species.

The most remarkable thing about spiders is the silk they make. We humans have not produced anything as strong, light and elastic. Spider silk is twice as strong as other silk producing insects like the silkworm moth.

 

Argiope sp. spider in Thung Yai Naresuan Wildlife Sanctuary

Besides the construction of webs, spiders have many other uses for their silk such as making nests, attach trapdoors, furnish burrows, and construct egg cocoons. Other uses are to wrap up and mummify their prey. It truly is some amazing stuff.

The coupling of two predatory and often shortsighted creatures can be a hazardous affair, particularly for the smaller male. In spiders, the battle of sexes is very intense and in some species, the male ends up being eaten after mating with the female. The size difference between the male and female can be seen in the photograph of the ornamental spider.

Spiders are extremely important in the balance of nature and play a big role in the elimination of vast numbers of pest insects. These unique creatures are allies of farmers and growers. Yet even if they were not useful, spiders would still deserve our whole-hearted respect as one of the most diverse and fascinating groups in the natural world.

 

Argiope sp. spider in Chiang Mai

Some people may disagree but if you bump into a spider, please let it go. These ancient creatures need our love and protection.

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