With cooler weather beginning to push into Southeast Texas, people begin to contemplate who or what they will be for Halloween. Ghosts and monsters generally come to mind but also creepy crawly things. Spiders fall under the category of creepy crawly and are often used as props to decorate for Halloween. And that is why this month, the focus will be on Arachnology - the study of spiders.
Spiders - Creepy Crawlers
Spiders are known as arachnids and belong to the order of Araneae. Although they may have some similarities, spiders and insects actually belong to two different orders and have several notable differences. Insect bodies are divided into three parts - head, thorax, and abdomen, whereas spider bodies only have two segments - cephalothorax and abdomen. Spiders walk around on eight legs attached to their cephalothorax while insects have six legs attached to their thorax. Though some spider species have six eyes, most species have eight eyes located on the front of the cephalothorax. In spite of so many optics, nearly all spiders have poor eyesight. An exception to this would be the jumping spider that has the ability to see colors beyond human capability.
Spiders are commonly known for producing silk, a protein fiber which is very strong and is used by its creators in many ways. Silk can act as a safety tether for climbing in case of falling and used to travel in the wind (called ballooning). It is also used to produce egg sacs, create traps for prey, bundle their prey, and of course, make a web. Not all spiders create a common web but all species produce silk of some kind.
To Fear or Not to Fear
Arachnophobia is the fear of spiders; however, the word ‘fear’ is an understatement for some when spiders are involved. The fear of spiders can be very irrational and intense as well as uncontrollable. In fact, you might be one who absolutely cannot stand spiders and would burn the house down to ensure the spider does not survive. For those who are unable to relate to arachnophobia, it might be better if facts and numbers are considered.
With the exception of Antarctica, spiders can be found throughout all continents. Population densities are greater in tropical zones over temperate regions. Most spiders are terrestrial with a few species that live on the edge or surface of fresh or saltwater. One species in Eurasia is an aquatic spider and survives in freshwater that is slow moving. There are over 50,000 species of spiders that have been recorded in the world that range in size from 0.011 inches (Samoan moss spider) to nearly 12 inches (Goliath bird eating tarantula). That's about 25 million metric tons worth of spiders in the world!
That many spiders may be daunting but there is good news about these amazing predators. With that many spiders around the globe, you can imagine they get hungry and they sure love to eat. Spiders in total can consume up to 800 million metric tons of prey annually. Spider food includes disease and virus carrying insects as well as agricultural pests. This would indicate that spiders are actually very beneficial for humans, even if they are scary by appearance and numbers.
The Value of Venom
What's For Dinner?
Depending on the species, spiders can capture their prey in any number of ways. Some spiders, like the jumping spider (pictured right top), capture prey via jumping on it. Some species ambush their prey, and others such as the orb weaver (right bottom), trap prey in a web of some kind. To the benefit of the spider, their venom immobilizes their prey and oddly enough, all species digest their food outside of the mouth. This is done by excreting an enzyme on the food that breaks it down as they chew or inject the digestive enzyme into the food source and they suck out the fluids. This style of eating may sound gruesome but it is an adaptation that suits spiders very well.
The Bites that Bite
Just about all spiders are venomous though very few species are harmful to humans. The most dangerous spiders in the United States are the Brown Recluse spider and the Black Widow spider. The Brown Recluse venom contains a protein that destroys the blood vessel walls meaning it kills tissue at the site. Toxins that do that are called cytotoxins. The bite location can develop a skin ulcer and/or become infected resulting in taking weeks if not months to heal.
Alternatively, the Black Widow bite produces a neurotoxin which results in severe muscle pain, difficulty breathing due to paralysis of the diaphragm, and nausea. Although it sounds horrible, most people recover without any complications.
Friend or Foe
You can ultimately decide if you like Arachnids or not but keep a few things in mind. Spiders really are beneficial creatures that help control insect populations but also serve as a food source for other organisms. These beautiful yet scary invertebrates add to the biodiversity of the ecosystem and play a vital role within the food web. Spiders may not get much love from humans but they do serve a purpose in nature. They also have their place in Hollywood as well as Halloween, and for that, we can be thankful for.
References and Resources:
- “Spiders Eat Astronomical Numbers of Insects.” ScienceDaily, ScienceDaily, 14 Mar. 2017, www.sciencedaily.com/releases/2017/03/170314111251.htm.
- “Spiders, Facts and Information.” Animals, www.nationalgeographic.com/animals/invertebrates/facts/spiders.
- “Spider.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., www.britannica.com/animal/spider-arachnid.