Desert Diaries

Desert Survival and Predator Avoidance

Avoidance: we all do it; it can be a part of every-day human interaction and life! One aspect of avoidance that thankfully is not a vital part of our daily affairs is predator avoidance. If you’re an insect, this means not getting the attention of another animal that would like to make a meal out of you. Insects in the Sonoran Desert need to address predator avoidance daily, hourly, and often they practice it every minute of every day in some way. One method that can be a very effective component of predator avoidance is mimicry. Why look like a delicious caterpillar to a bird, when you can mimic the motionlessness and the appearance of a thorn on a plant? Looking like a thorn means you’d better act like one to pull off the ‘trick’ of fooling the ever observant and sharp eyes of a hungry bird!

These Geometrid moth caterpillars do exactly that. In size, shape and color they resemble the thorns of the plant that they eat, but that may not be enough if they are always moving around. To complete the deception, they will hang onto the plant with only their rear set of legs, and angle their bodies off the stem at a similar angle to the thorns of the plant, remaining absolutely motionless for minutes at a time! This combination of appearance and behavior makes for very effective ‘thorn mimicry’, and increases the caterpillars’ chances of becoming a moth one day!

Written by: Howard Byrne, HIIZ Keeper