Do Spiders Have Lungs?
WouterSpiders are unique in that they have two types of breathing apparatus. One of them is called trachea, and the other is called book lungs.
The trachea is a series of small tubes that run through the spider. They are designed to allow the spider to get oxygen into its body, but they don’t actively pump air. Unlike vertebrates, spiders breathe through passive diffusion. This allows them to go hours without a breath.
Book lungs are located at the front of the spider’s abdomen. These lungs are made of thin, hollow plates, and they are surrounded by a layer of hemolymph, similar to blood. During periods of activity, some spiders open wide lung slits.
Some species have two pairs of trachea, while others have only one pair. Those with only a single pair tend to have lower metabolic rates. It is possible that spiders with only a single pair of trachea were formed through direct evolution from spiders with two pairs.
As a result, some spiders have wide lung slits during short periods of activity, while others have slits that are only slightly wider. However, in all studied species, the lung slits open if the spider’s blood oxygen levels fall too low.
In most arachnids, the book lungs are the most important respiratory organ. This is because they have a large surface area for gas exchange. While arachnids don’t need to actively pump air, they do need to move in order for the book lungs to work properly.
