Some of us that were still growing up before the age of the internet and technology might still recall playing a game called follow the leader. Here at the Hoedspruit Endangered Species Centre a very interesting phenomenon has caught our attention. Some caterpillars seem to have started playing “Follow the leader”!
These are of course commonly known as processional moths, although it is the caterpillars that people are mostly noticing. These convoys are found crossing roads and pathways in a single line where they follow each other in a head-to-tail procession. Some of these processions have been known to consist of up to an astonishing 600 caterpillars.
According to Field Guide to Insects of South Africa they belong to the family Thaumetopoeidae that is considered by some to be a subfamily of the Notodontidae. There are that species that are known in the region with the most common being the Reticulate Bagnet (Anaphe reticulata).
The larvae are more conspicuous than the adults due to their gregarious behaviour. They are quite hairy and form these congregations to ward off predators and find food and it appears that they feed on a wide variety of plant species. As they usually get together in very large numbers, they easily strip the host tree of all its leaves. However this is a natural phenomenon and trees perfectly capable to recover without any long-term damage having been done.
The larvae are mostly active during the colder times of the year. During the day they will be found congregating in the trunks of the food plant that is mostly the Wild Pear Trees (Dombeya) and Horn-pod Trees (Diplorrhynchus). They move from tree to tree in trails that is formed with silk which is laid out by the leader. This does not show them the way, but rather acts as a gripping mechanism for the followers. Pheromones and tactile stimulation by the setae of the preceding caterpillar determines guidance for the group.
These caterpillars also pupate together when fully grown when they form the silken cocoons that are compacted together, all within an outer tough envelope. These bagnet structures are what gives this family of moths their and are very strong and up to 600 larvae may contribute to a single bagnet. The silk in these bagnets are littered with the larval body hairs that they shed when they pupate. Some have tried to harvest these silk nests for the silk trade but the cost of extracting these hairs would have been prohibitively expensive. As with most of the hairy caterpillars these hairs serve as protection against predators and other curious investigators. Animals such as dogs that might be intrigued by the procession tend to end up at the vets as they may pick up the hairs onto their paws which they lick as it is very irritating. Once the hairs are on the lips/tongue it will induce itching, swelling and possibly vomiting.
A similar family known as the pine processionary caterpillar can also be found in the Northern Hemisphere and it is one of the most destructive species to pines and cedars in Central Asia, North Africa and the countries of southern Europe.
There are so many fascinating phenomenons all around us as nature is full of surprises. There is never a dull moment out here as we find and learn something new and interesting everyday if you just look around you.
Field Guide to Insects of South Africa
By Mike Picker, Charles Griffiths, Alan Weaving