A saguaro boot is the hard shell of

callus A callus is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may o ...

tissue, heavily impregnated with

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...

, that a

saguaro The saguaro (, ) (''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...

cactus A cactus (, or less commonly, cactus) is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word ''cactus'' derives, through Latin, from the Ancient Gre ...

(''Carnegiea gigantea'') creates to protect the wound created by a bird's nesting house . The bird pecks through the cactus skin, then excavates downward to hollow out a space for its nest. When the saguaro dies, its soft flesh rots, but its woody infrastructure lasts much longer. So does the hollowed-out callus whose roughly boot-like shape gives it the name of "saguaro boot." Several different kinds of birds create nest holes in saguaro cactus. The

Gila woodpecker The Gila woodpecker (''Melanerpes uropygialis'') is a medium-sized woodpecker of the desert regions of the southwestern United States and western Mexico. In the U.S., they range through southeastern California, southern Nevada, Arizona, and New M ...

(''Melanerpes uropygialis'') creates small holes (about 5 cm across) at midlevel on the cactus, where the ribs are far apart, feeding on larvae under the cactus skin. The larger

gilded flicker The gilded flicker (''Colaptes chrysoides'') is a large-sized woodpecker (mean length of ) of the Sonoran, Yuma, and eastern Colorado Desert regions of the southwestern United States and northwestern Mexico, including all of Baja California, ex ...

(''Colaptes chrysoides'') drills bigger holes higher up, where ribs are close together, because its beak is strong enough to break through rib tissue. The saguaro responds to the bird's damaging its tissue by secreting a resinous sap that, over time, hardens into a bark-like shell that prevents the cactus from losing fluid and also protects the nest hole by making it waterproof. The bird's nesting hole requires not only the bird's making a hole but also the cactus's lining the hole - it is not ready for use as a nest until a year after its creation. Many saguaros are home to multiple nests; if birds excavate adjoining hollows, a saguaro boot may be formed with more than one opening. Native Americans of the

Seri Seri or SERI may refer to: People *Jean Michaël Seri, an Ivorian professional footballer Places *Seri Yek-e Zarruk, Iran *Seri, Bheri, Nepal *Seri, Karnali, Nepal *Seri, Mahakali, Nepal *Seri, Raebareli, a village in Uttar Pradesh, India Oth ...

group used saguaro boots to store or carry water. It is now illegal to collect saguaro boots from the wild in Arizona. Some desert moth caterpillars also make tunnels inside saguaro cactus. The resulting dried callus that forms around their tunnels has a flattened disk structure where the caterpillar exits instead of the larger hole seen on a saguaro boot.

References

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Gallery

File:SaguaroBoot_2.jpg, Saguaro boot with US quarter to show scale File:SaguaroBoot_1.jpg, Slightly different viewpoint of same saguaro boot File:DBG SaguaroBoot.jpg, Saguaro boot with saguaro. Boot toe should point down, not up. File:DBG SaguaroBoot3holes.jpg, Three nest-holes united into one saguaro boot File:Dead saguaro1.jpg, The bare wooden ribs of a dead saguaro File:Saguaro1.JPG, Saguaro with nest holes File:Gilded Flicker (Colaptes chrysoides) by nest hole in saguaro cactus.jpg, Gilded flicker by nest hole in saguaro cactus File:Melanerpes uropygialis Tucson AZ.jpg, Gila woodpecker on cactus File:SaguaroInsectDamage.JPG, Saguaro with dime-sized rosette from caterpillar exit hole File:HoleLivingSaquaro.JPG, Close-up of living saguaro with hole, wound-response

, quarter shown for scale File:HoleLivingSaguaro2.jpg, Longer view of living saguaro with hole seen in previous close-up File:Jefftimscactus.jpg, Looking up a saguaro Bird breeding Flora of Arizona Flora of the Sonoran Deserts Flora of the Southwestern United States North American desert flora Cacti of Mexico