Flies as food

This morning I had to catch a fly, any fly of a decent size, to feed a jumping spider I wanted to photograph (jumping spiders are almost too easy to photograph; they have such great faces!). While I was looking for a fly, I got to thinking about a frequent question: what good are flies? Or, a variant, “what are flies good for?” Or, even more direct, “what are flies for?”

Of course, such questions are related to human values. As scientists, we usually don’t think that way; hence the common sarcastic answer “what good are humans?” What people mean by these questions, I suppose, is what “role” do they play in the environment. One of the answers that I read frequently in textbooks or the popular press is that flies and other insects are important as “food for birds and other animals.” I hate this answer. It is as if other animals, especially birds, are more important or significant than insects. In this way, the incalculable goods and services provided by flies, such as pollination and breakdown of organic materials, can be discounted, and flies dismissed as just obnoxious pests.

Humans are so oriented towards the macro organisms in the environment. There is so much more to see and admire if we look a little closer at the smaller things. There are about 10,000 species of birds in the world, but at least 150,000 described species of flies. One of the largest families of flies, the Tachinidae, has at least as many species as the birds, but doesn’t even have a common name! We scientists have to promote more fly literacy.

I caught a fly for my spider, a common blowfly, Lucilia sericata– a “greenbottle fly” to most people. I know what my spider thinks it is for.