Thursday, 21 June 2018
Bizarre dispersal mechanism
It is amazing how, when one finds out something about wild things, the answer leads to more questions. Like Kipling's Elephant child some of us have ' satiable curtiosity', but we no longer risk corporal punishment with all our annoying questions. We simply turn to Google. This is how things happened.
A local lady, Wendy, asked me to identify this beautiful caterpillar she had photographed in her recently planted woodland. It turned out to be a Mottled Umber. I've only ever caught one adult moth in my moth trap. It is a woodland species and flies in mid-winter. Only the males have wings (as with the Winter Moth). What the female adult does, when she emerges from the pupa, is to climb up the trunk of a tree and perch on a twig looking far from pretty, but releasing pheromones which the males find attractive. Mating takes place and the eggs are laid. Next summer the caterpillars hatch and eat the new leaves on the tree.
This is fine, but how, I asked myself, did the species get to Wendy's Wood? It would take years for a female to crawl there from the nearest woodland. Nothing helpful in my books. The Internet came up painlessly with what the crocodile has for breakfast. Richard Fox, a big name in the moth-ing world, describes a bizarre strategy that wingless moth species have evolved for dispersal. Some eggs are laid on the tree where she mated. But then to seek woodlands new for her species she offers herself to be eaten by birds such as Tits. She wriggles like a mealworm to make sure she is seen. The fertilised eggs in her body pass through the guts of the bird. The bird flies off, perhaps to another wood and disperses the species.
I haven't got a photo of a female Mottled Umber moth, but this Winter Moth looks very similar. Melvin Grey found it by watching male Winter Moths and searching twigs by torchlight.