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What Are Tarantula Book Lungs?

Spider on tiny steps

In a previous article, I talked about bioactive setups for invertebrates. You can find that article here. One of the reasons bioactive terrariums are beneficial for arachnids in particular is that it helps them to breathe by adding more moisture to the environment and even indicating when the habitat is dry.

The reason humidity levels are so important to respiration for animals like tarantulas is because they breathe through sets of organs called book lungs. This article covers more on what book lungs are and how tarantulas and other arachnids use them to breathe.

Book lung structure

Tarantulas have two sets of book lungs, for four book lungs in total. This number actually makes them fairly unique among spiders. Most other arachnids only have one pair of book lungs, and some spiders have no book lungs at all, instead breathing through tracheal tubes, like insects do.

Each of these book lungs is contained within a solid pocket on the tarantula’s abdomen, and on the inside of these pockets, the book lungs look like...well, books. That is, they are arranged in layers that resemble enclosed pages.

Book with open pages

Oxygen is diffused between these “pages,” which are called lamellae.

Differences with book lungs

By the physical description alone, you may have noticed that tarantula’s lungs are much different from the kind we have. They also function differently, and because of that, they have different advantages and disadvantages to the animals.

Although all respiration uses up water, breathing with book lungs generates greater water loss than using the kind of lungs mammals have. That’s part of the reason why it is so important to keep your spider’s humidity levels high enough and to provide substrate they can burrow in. They need that moisture to breathe properly.

Tarantula on mossy ledge

Another difference is that tarantulas and other creatures with book lungs, such as scorpions, don’t actively pump air into their bodies like mammals. That is, they don’t fill their lungs with air. Instead, they breathe passively; air simply enters the book lung openings and is diffused through their blood (though technically, they don’t have blood either, possessing instead a blood-like substance called hemolymph). Tarantulas do, however, open the lamellae wider in certain situations in order to take in more oxygen.

Knowing how your spider’s body works can help you be a better tarantula keeper. Do you provide live plants in your spider enclosure or do you use a different method to maintain healthy humidity levels? Let us know on The Tye-Dyed Iguana Facebook page.