Friday, May 18, 2012

Life of a Cactus Part 4: Spines

The red, hooked spines of a Barrel Cactus.

Obviously, spines also are a major deterrent to any creature wanting to access the cacti’s rich moisture reservoir.   Many animals still consume cacti anyway.  Prickly pear pads are a staple to javelin.  During extreme drought many animals including packrats and mule deer will consume cacti to obtain water.  I have found entire barrel cacti hollowed out in the inside by rats or chipmunks eating the inside tissue to obtain water during extreme droughts.  Mule deer and javelina supposedly will remove cacti spines with their hooves before eating the tissue.  So under extended dry conditions animals are willing to brave spines and oxalic acid to obtain water.  A few cacti, have such a huge density of spines very few animals ever dare go near them.  The teddy bear cholla is one such example, while the huge density of spines may look fuzzy and attractive like a teddy bear from a distance, one encounter with this cactus will deter you forever.  Teddy bear and jumping chollas both have spines that are microscopically barbed or hooked like fishing hooks.  So it is much easier for these spines to penetrate skin rather than be removed.  I often step on teddy bear cholla joints which isn’t so bad being I have shoes on, but once I accidently bumped a joint on my shoe into the calf of my other leg.  Removing the spines was excruciatingly painful and difficult due to the barbed spines.  Then, the day after, I developed one of the most amazing bruises right were the joint was stuck in my calf.  The bruise changed from blue and black to yellow and green over time, and to say the least I learned my lesson and stay as far away from teddy bear chollas as possible.
Buckhorn Cholla cactus.
Obviously, spines are used to deter animals from eating cacti, but they have a few far less obvious but still very useful functions also.  Spines actually provide a significant amount of shade, helping to cool the plant and therefore prevent water evaporation.  The shade also protects cacti from intense desert sun which could damage the plant.  Spines also provide a sort of shield protecting the cactus from dry desert winds that might “steal” moisture.  Spines can also serve as insulation, preventing freezing temperatures from freezing and damaging the cactus.  Some cacti utilize spines to the extreme.  Teddy bear chollas are so dense with spines nothing can even begin to try and touch the green portions of the plant without first going through the spines.  Small pincushion cacti are also quite dense with spines.  These spines greatly reduce the amount of light reaching the plant, cooling temperatures slightly, as well as slow the wind.  Barrel cacti also have a higher density of spines on their tops where the growing tissue is located.  This protects the growing tissue from intense sun, extreme temperatures, and dehydration so the plant can continue to grow.  Senita cacti also often have a dense almost furry looking accumulation of spines near their tops.  
Close-up of a Buckhorn Cholla.

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