Many people believe that spiders must be able to hold their breath because they often survive a spray of insecticide or being underwater for a long period of time. This has become a wide-spread myth that Rod Crawford at the Burke Museum has set out to dispel. He says, “Neither spiders nor insects actually breathe, therefore they cannot hold their breath.” We will examine how spiders breathe and what you need to know about spider control to make it effective.
Spiders do not actively pump air in and out of their bodies. Instead breathing takes place through a kind of passive diffusion. Arachnids have two types of “breathing” apparatuses. The first are called book lungs. Although they are referred to as lungs, they have little resemblance to human lungs. Book lungs look like the pages of a book. Each “page” is a hollow, air-filled plate that is open to the air through slits on the abdomen. Hemolymph (spider blood) surrounds the inner surface of the plates and hemocyanin (similar to red blood cells) carries oxygen and exchanges carbon dioxide. The slit openings of the book lungs can expand and contract, but never fully close.
The second way spiders breathe is with trachea. These are very small tubes that branch out, often from the book lungs, and run throughout the body. Tracheae allow the passage of air and open directly to the surface through small holes called spiracles. Some spiders only have one trachea and no book lungs, and other spiders have 1 or 2 book lungs.
Since spiders do not actively breathe and cannot hold their breath when underwater, why can they survive these things better than other bugs? Crawford says it is because sometimes body hair on a spider can trap air and make a film that can exchange some oxygen and carbon dioxide with the surrounding water. This does not work long-term, but spiders can go for many minutes fully submerged.
As for pest control, spiders are not insects and often do not behave in the same way as insects. While most of the insecticides will work with direct contact, other methods of spider control like diatomaceous earth, sealing the exterior of your home, removing webs, and replacing outdoor lighting may prove more beneficial. Spider traps are also great for monitoring the population within your home. Harris Spider Killer is another great option. For more information on dealing with spiders, check out Spiders: The Ultimate Guide.