Spiders are often feared and sometimes scorned, but they do serve a purpose on our planet. Did you know that this order, Araneae, is the largest entirely carnivorous group of animals on the planet? Without spiders, insects would soon reach pest proportions. Most people can recognize a spider, even without knowing the characteristics that members of the order Araneae share.
Spiders are not insects; spiders belong to the class Arachnida. Like all arachnids, spiders have just two body parts, a cephalothorax and an abdomen. In spiders, these two body regions join at a narrow waist, called a pedicel. The abdomen is soft and unsegmented, while the cephalothorax is harder and includes the eight legs that characterize spiders.
Members of the order Araneae prey on other organisms, usually insects. However, spiders can only consume liquids, as they lack chewing mouthparts. They use chelicerae, pointed appendages at the front of the cephalothorax, to grasp prey and inject venom. Digestive juices break the food down into liquid, which can then be injested by the spider.
Most spiders have eight simple eyes, although some have less or even none at all. When trying to identify a spider, observing the number and arrangement of the eyes is an important detail to note.
All spiders make silk. Usually, the spinnerets are under the tip of the abdomen, allowing them to spin a long strand of silk behind them.
Habitat and Distribution:
Over 40,000 species of spiders inhabit most of the world, including the Arctic. The vast majority of spiders are terrestrial, although a few specialized species live under water.
Major Families in the Order:
Families and Genera of Interest:
- Female flower crab spiders, Misumena vatia, change colors from white to yellow to match flowers, where they lie in wait for pollinators to eat.
- Members of the genus Celaenia resemble bird droppings, a clever camouflage that keeps them safe from most predators.
- The ant spiders of the family Zodariidae are so named because they mimic ants. Some use their front legs to mimic antennae.
- The magnificent spider, Ordgarius magnificus, tricks its prey by setting a silk trap with a pheremone that mimics the moth's own. Male moths are lured to the trap by the prospect of a female, and quickly subdued by the spider.
- Insects: Their Natural History and Diversity, by Stephen O. Marshall
- Australian Museum - online fact sheets