The Spider and the Fly

A spider preys on a long-legged fly.

Sights like the above are common in sweep nets.  I am always amazed by just how many spiders of all sizes I sweep up in a net, and generally most of them take advantage of the opportunity to grab a fly or other small insect.  Sometimes they even grab another small spider!  Not all spiders use webs to catch their prey–many actively hunt and tackle their prey, bringing them down with a quick venomous bite.  The spider above has grabbed a small0 metallic green fly, specifically a ‘long-legged fly.’

The long-legged flies belong to the fly family Dolichopodidae, from the greek word “dolicho” meaning “long” and “pod” meaning “foot” or “leg.”  (Think of a podiatrist.)  This is a diverse and speciose group, but many members are easy to recognize thanks to their slender bodies, long legs, and frequent metallic coloration.  Interestingly, both the larvae and the adults of this family are predators, hunting and eating other small animals.  In this role they can help to regulate populations of pest species such as mites and tree pests.