Hitching a ride...

Yesterday Ceridwen blipped a rather beautiful violet ground beetle Carabus violaceus, that had taken up residence in her fruit bowl. This is a very closely related but somewhat less common species, Carabus problematicus, which we found yesterday in Norfolk.

I didn't have the right equipment to photograph it in the field, so we brought it home for its photoshoot. Like many large beetles it has an associated fauna, a group of mites, one of which can be seen just behind the left eye.

It seems logical to think that these must be harmful to the beetle in some way, but in fact this is a special example of a relationship known in ecology as commensalism, where one organism uses another without causing any apparent harm. Often this is associated with food, for example remora fish on sharks. Like all ecological interactions, commensalisms vary in strength and duration from intimate, long-lived symbioses to brief, weak interactions through intermediaries.

In this case the relationship is all about transport, and is known as phoresis. Mites are not very mobile, and its much more efficient to hitch a lift from a much larger and more agile invertebrate in order to colonise a new area. These mites will now be living somewhere in our garden, along with their carnivorous host, which will find plenty of suitable food and habitat, and may even hopefully control a few pests.