Stinging nettles hold no fears for caterpillars
In New Zealand there are two native butterflies known as the red admiral and the yellow admiral.
The caterpillars of both species feed on the tree nettle which is found mainly on the fringes of our native forests and in damp scrub areas. It is difficult to distinguish between the two species in the caterpillar stages. Most likely the one in the photo is a red admiral caterpillar as adults were flying in the vicinity.
Admiral caterpillars grow through five stages called instars. At the end of each stage they moult and expand to a larger size. The colouring of this caterpillar indicates that it's at the last stage and will soon pupate and change into an adult butterfly.
As can be seen in this photograph, the stems and leaves of this stinging nettle produce many stinging hairs which are tipped with very sharp spines. Even a light touch can result in the spines penetrating human skin causing pain and numbness that can last for several days. Severe stinging can cause paralysis and even death. It's a dangerous plant.
These caterpillars, however, can crawl over the stinging hairs with no apparent consequences. Somehow they are immune and it may well be that medical science will, in the future, identify an antidote for human use.
Notice that this caterpillar has spines in its back that are of similar design to the nettle spines.
In effect the caterpillar is saying to hungry birds, "keep away, I might sting".
The Southland Times