Passengers

By Ruth D’Alessandro, The Wildlife Gardener What is the similarity between these two pictures?

 

Believe it or not, they are both pictures of passengers. People getting on a Surrey bus, and mites getting on a Surrey crane fly. Apparently my Mummy-Long-Legs was not carrying eggs, but mites. Mites belong to the class Arachnida, like spiders and scorpions. They can be parasitic, like the varroa mite that devastates bee colonies, or not, like the microscopic house dust mite that feeds only on shed flakes of human skin and goes unnoticed unless someone is allergic to its droppings. So how can mites get about? Well, my new word of the week is’phoresy‘: one animal attaching itself to another for transportation only. The mites clamber aboard a bigger, more mobile animal and hitch a lift. When their transport arrives at where they need to be, the mites disembark. The passengers are phoretic. So what’s in it for the carrier insect? A rather entertaining example of phoresy can be found in Sexton, or Burying beetles (Nicrophorus sp):

Yet even with this burden the beetle will find its way to a decaying corpse of a mouse or bird. Upon arriving at the corpse, the mites will disembark from the beetle and eat any maggots. The beetle will lay eggs on the corpse and bury it by gradually excavating the soil underneath it. By eating the competing maggots, the mites leave more food for the beetle larvae. The Sexton beetle and the phoretic mites have a symbiotic relationship: they get mutual benefit from their association. So what – if anything – could possibly be in it for the Surrey crane fly? It obviously waited patiently for so many mites to climb aboard, and that weight of phoretics must make flying less easy. Does altruism exist in invertebrates? I think not. But if any of our wonderful Naturenet readers can suggest a destination for the mites, please let us know.