I came across a fascinating example of a mutualistic symbiotic relationship today in my back yard. Unfortunately, the few photos I was able to take did not turn out well. However, even without adequate visual support, I though this interesting enough to post anyway.
This is a sexton beetle (genus Nicrophorus). It is covered with mites. The sexton beetle is part of the family of carrion beetles, which brings me to what the mites are doing on the beetle. The mites are allowed to be passengers on the beetle and are transported to a place where the beetle has buried a small vertebrate carcass that it has formed into a “brood ball”.
The carcass contains a rich food source where the mites can gorge themselves on delicious insect eggs and maggots. But the beetle does not provide free airfare, and buffet out of the kindness of his heart. By bringing the mites along, the beetle is assured that other insects will not develop to compete with its own offspring within the brood ball.
There is even a name for this type of phenomenon in which one species attaches to another to be flown to a food source. It is called phoresy. Phoresy is more commonly associated with commensalism rather then mutualism, but in this case the beetle definitely receives a benefit due to the association.
I must note that this particular beetle carried what appeared to be an excessive amount of mites. My brief observation showed that, although the beetle made several attempts to get airborne, he was not able to. The beetle was not only weighed down with phoretic mites, but they were so numerous that he was not able to open his wings. There were also a large number of mites on the beetle’s underside.
I was amazed by how the mites were able to cling on to the beetle as he moved around. I did not witness a single mite fall from its living taxi during my short encounter.
And in the end, the father beetle finds a way to fulfill his obligation and brings mites back to the brood ball. Now these tiny creatures (the grubs and the mites), through a tradition of inter-species cooperation, have a chance to live on, and pass this tradition on to the next generation.
To read a more detailed description the beetle’s life cycle go to Burying Beetle.