An introduction to spiders

Why we should not fear them

by Sasha Remnant

Araneae an order from the class Arachnida, more commonly known as spiders can be found with the exception of Antarctica, on every continent on the planet.

 

For most people, spiders arouse mixed emotions. Many of us marvel at their complex and shimmering webs. On the other hand, many of us are terrified by their painful and potentially fatal bites. Contrary to popular belief, the effects of most bites are not serious and a lot of ‘spider bites’ may be over diagnosed or misdiagnosed. In many reports of spider bites, it is unclear if a spider bite has actually occurred.

 

Fear of spiders amongst the general public is not unusual. However, most people can overcome their fear of spiders once they become familiar with them. Spiders play an essential role in the Earth’s ecosystems; these colourful, fascinatingly beautiful creatures certainly deserve closer inspection.

Image by Vidar Nordli-Mathisen

Recent studies suggest spiders are thought to be one of the most important groups of natural enemies to insects worldwide. An estimated 400-800 million tons of prey are annually killed by the global spider community; to put that into perspective the world human population consumes an estimated 400 million tons of meat and fish annually.

 

Spiders have an enormous ecological significance serving as important pest and disease management through controlling insect population. Furthermore, they serve as a crucial source of nutrition for an incredibly diverse complex of arthropod-eating carnivores. Countless species of birds, mammals, reptiles, and amphibians feed heavily on spiders, even fish have been reported to consume spiders which have mistakenly landed on the water surface.

 

Spiders are one the most diverse groups of arachnids. Their population can be huge, possibly more than five million per hectare in temperate grassland. As a result, they have significant impact on agricultural productivity. It has been proposed that the population of spiders in Britain consumes more insects each year than the weight of the population of people. 

Image by Ed van duijn

 Araneus diadematus (European Garden Spider). Photo by Ed van duijn on Unsplash.

A common misperception of spiders is that they are merely slightly odd insects that have an additional pair of legs and wings. This misunderstanding could not be further from the truth. They have evolved independently from insects for hundreds of millions of years, with the oldest fossil of a true spider believed to be from about 300 million years ago long before the first modern humans existed. Most of the earliest segmented fossil spiders belonged to the Mesothelae group of spiders with spinnerets (silk-spinning organ) placed underneath the middle of the abdomen, rather than at the end like modern spiders. Above all, they differ from insects in their ability to produce silk and in injecting venom through their fangs to immobilise prey. Although there are some insect groups which do produce silk for example, to provide a protective cocoon for the pupae in butterflies and moths, spiders use silk in almost all aspects of life. Silk has been put to many uses by spiders, including protection of eggs, mating, prey detection, making retreats and, most obviously, to entangle and catch prey. They can survive under extreme conditions and disperse by ballooning, a process allowing them to become airborne and travel from place to place via silken threads. This has enabled them to colonise a wide variety of different terrestrial habitats. 

Glistening Spider Webs

Spiders are classified into two main types by the way they use their fangs. Mygalomorph fangs hinge downwards and araneomorph fangs hinge together sideways. Most of the spiders that people encounter in daily life belong to the Araneomorphae infraorder of spiders. We only have one Mygalomorph (tarantulas and their close kin) found in the UK, the Purse Web Spider. This species is mainly found in Southern England which spends almost all of its life inside its purse-web, consequently it is a rarely seen species.

Araneae have astonishing morphological variation and can be categorised into 120 families with over 48,200 species worldwide. But, there may be more than 120,000 species across the planet, of these, over 670 species (34 families) have been recorded in the British Isles. The British spider fauna is dominated by money spiders (Linyphiidae) some of which are only 1mm long, which account for over 40% of our spider species. This is a significant contrast to species found in warmer areas of the world where members of the linyphiids family typically form a smaller proportion of all spiders. For example, they constitute to only 7% of the Greek spider fauna. Linyphiids species are small and are found in virtually every possible habitat, trees and shrubs but the majority live on the ground surface, in leaf litter or even in soil. Unlike Linyphiids, the British Orb-Weaver family Araneidae are commonly found in trees and shrubs as opposed to on the ground.

Almost everyone will be familiar with the European Garden Spider which is widespread and abundant throughout Britain. These types of spiders build spiral wheel-shaped webs often found in gardens, fields, and forests. The wolf spiders (Lycosidae) do not build webs and are almost exclusively ground-active, they are characteristically diurnal (active by day) hunters with well-developed eyes and excellent eyesight used for hunting prey. Females can be immediately recognised in the breeding season by their habit of carrying an egg sac attached to their spinnerets (silk-spinning organ) which is an unusual behaviour almost confined to this family.

Jumping spiders (Salticidae) are perhaps our most unique family of spiders, with excellent eyesight allowing them to stalk and capture their prey and are entirely diurnal hunters. The crab spider, Thomisidae, represents a completely different diurnal hunter they do not build webs to trap prey; some sit on or beside flowers as pictured where they grab visiting insects with some species even being able to change colour over the period of a few days, such as Misumena vatia. While this family overview is only brief, it can demonstrate spiders diversity of body form, prey-capture strategies, and ecological adaptation.

Image by Егор Камелев

Crab spider, a spp. from the Thomisdae family. Photo by Erop Kameneb on Unsplash.

As the temperature drops in autumn, spiders become more active, looking for a mate, and come out of their hiding places which is why it is more common to see them in your house. Towards the end of autumn many die off, but some hibernate until the following spring.

 

If the autumn season was spent honouring and learning more about spiders, we may find ourselves overcoming the fears we have towards them.