A few days ago I was out walking the dog when we came across a bunch of caterpillars crossing the road. These were processionary caterpillars and are a familiar sight in this part of the world particularly at this time of the year. They walk in a line one after another, a habit that gives them their common name. They produce a trail of pheromones but it is the hairs at the rear of the caterpillar in front provide the main stimulus for the caterpillar following behind. Even though I have seen this behavior many times I had never stopped to consider WHY they should be marching in a procession like this away from the pine trees on which they grow over the winter.
So why DID the caterpillars cross the road? Continue reading

