1. Two segments body
2. Eight legs
3. Simple eyes
4. No antennae
5. No wings
1. Three segments body
2. Six legs
3. Compound eyes
5. Wings (in some cases)
Some spiders might differ from others in terms of shape , color and size, but overall they share the same basic anatomy. Their body structure is divided in two sections.
The Cephalothorax is the front section which includes the brain, stomach, fangs, chelicerae, glands that produce venom and eyes, which are simple, not like those of insects which are compound. Eight legs to walk and two palps that help in mating and holding the prey are attached to this seccion as well.
The second section is the Abdomen containing the spinnerets, the glands that produce silk, heart, intestine and ovary among others.
Spiders, like other arthropods, don´t have an internal bone structure, but they are covered by a hard exoskeleton which they shed each time they moult, allowing them to grow.
Though spiders and insects are both groups of arthropods, they are not the same, each one belonging to a different class. Spiders belong to the Arachnida and insects to the Insecta, yet people often confuse them. Understanding basic information about their main differences might help with a correct identification.
Illustration by Sergio Grez
The importance of spiders lays mainly on the impact they have in our world as natural pest controllers. What spiders do to keep the environment from becoming unbalanced is a job that people often underestimate. Spiders help in reducing the likelihood of plagues, diseases and famine.
When we talk about spiders keeping the environment balanced it is because they are prey for birds and other animals, but at the same time, Spiders are the main predators of insects and other arthropods. Many of these animals represent a threat to crops, so in a few words, spiders are the ones that keep those crops in good shape for humans.
Spiders are also a great help for gardeners by controlling pests that ruin flowers and plants. So if you want a beautiful garden, don't think twice, spiders are your best allies.
They can also keep your house free of unwanted insects and diseases as well. In some parts of the world, spiders are great at controlling the numbers of mosquitoes that spread Malaria.
Currently, spiders are being studied by many scientists who think they can be helpful to humans in many other ways. For example, spiders' silk has been shown to be stronger than steel and even more elastic, which makes it of great importance to the future of the building and engineering industry. Also of great interest is spider venom which scientists say could lead to new discoveries in the medical field and treat many diseases.
Spiders are marvellous creatures with many mysteries yet to be told. As time passes by and new discoveries are made we are beginning to understand how linked we are to spiders and the importance of having them around us.
Spiders are fascinating in many aspects, yet people often look at them with fear. This might be a behavior we learn as kids when we see others reacting badly to a spider. In some way I understand this fear because as humans, we see other species that differ too much from us as possible threats and even more when it is known that animals like spiders can sometimes inflict venomous bites, even though the dangerous ones are actually just a few. Spiders might seem like strange creatures we are not able to see and control and the feeling of a silent spider roaming our room can definitely give us second thoughts, but the truth is spiders won't try to bite for the sake of it, they run and hide instead. Spiders are true masterpieces of nature and there is certainly more to learn and treasure than there is to be afraid of.
Spiders have been around since before dinosaurs and it is estimated that the first species evolved about 380 million years ago. As conditions changed, so did the insects they fed on and slowly spiders advanced their capacity to build webs and other complex ways of catching their prey. In the present day, spiders have developed many different behaviors that allow them to continue as one of the most successful groups that have ever lived on earth. Some build amazing orb webs to catch flying insects, some change their colors to match the flower they are sitting on so they can ambush their prey, others master the technique of building a net between their front legs and then throwing it over the victim. There are spiders that hunt down their food and others use the tactic of waiting in a burrow and then striking when an insect passes by.
In the next taxonomic map we can see where spiders and relatives come from.
In many cases male spiders can be substantially smaller than females and often the process of mating can become quite a challenge for them. Certain females have been known to eat their male mates and this is why males must be careful to send the correct vibrations along the web when approaching the future mother. By doing so, the female wont confuse them with trapped insects.
Female spiders, depending on the species, will lay sometimes hundreds or even a thousand eggs once or twice a year. They will cover or wrap these in a silken cocoon that will be hung, attached to vegetation or hidden.
Once spiderlings hatch, they will come out of the egg sac and see the light of the world for the first time. At this moment, some mothers are so tired due to the big effort that they will shortly die after placing the eggs, leaving them on their own, but there's one species, the Wolf Spider, which is an amazing and beautiful case where a mother carries the egg sac attached to the spinnerets and when spiderlings come out, she carries them over her body until they are developed enough to start their own life.
When spiders begin their new life they will need to feed and the menu is a big variety of arthropods and even some small vertebrates, but with food and age comes the necessity to grow. As spiders are covered with a chitin exoskeleton, the only way to keep growing is to shed their skin and when they do, it is the moment when they are more vulnerable to being eaten by predators. After some time the new exoskeleton will harden and the spider will be safe again.
Female and male
about to mate
Female theridiid holding her eggs sac in her jaws
from the egg sac
Exoskeleton after molting
Spider at its adulthood