On Treehoppers…or…What the Heck is THAT For?!?!
One of the great ironies of the insect world: the group of bugs that is arguably the most charismatic, the most bizarre, and the most alien-like on Earth is unknown to most people. Easily overlooked because of their small size and the fact that they don’t bite or sting people, treehoppers are entomologically famous for their often fantastic and elaborate shapes. Treehopper species in North America (including North Carolina) tend to be rather sedate in appearance, but many of their tropical counterparts have been described, with good reason, as “mild-mannered minimonsters”. Some of these things really have to be seen to be believed…
As with the spittlebugs (the subject of a previous blog post), treehoppers are part of the insect order Hemiptera, characterized by having their mouthparts evolved into a permanent ‘straw’…an adaptation for sucking up liquid food. And like those crazy spittlebugs, treehoppers are exclusively vegetarian, eating only plant sap (although these critters eat phloem sap, rather than the xylem diet of spittlebugs).
What marks treehoppers as different from other insects is the extreme plasticity of one of their body parts. One of the parts of their exoskeleton…the top part of their thorax just behind the head….is called the pronotum. Basically, think of this part as their ‘upper back’. For some unknown reason, this pronotum is amazingly variable across species. And by ‘amazingly variable’, I mean that this structure looks totally and completely different in insects that are closely related to each other. In some cases, researchers believe that these extravagant forms have evolved to provide camouflage and protection for the bugs.
For example, species in the treehopper genus Umbonia are convincing thorn mimics whereas species in the genus Cladonota resemble bits of twig and bark. Species in the genus Heteronotus are über-convincing wasp or ant mimics. However, the outlandish shapes displayed by some treehopper species defy our attempts at explanation, leaving it up to our imaginations to decipher their adaptive advantage (Bocydium…what the heck is THAT for??)!
I’ve been fortunate to have chosen treehoppers as one of my research subjects. I describe their biodiversity and study their biology by reconstructing their family tree….their evolutionary background. Once we know about the evolutionary history of a group of organisms, we can study (and say something meaningful about) their biology and geographic distribution. And when the organisms you study are as wacky as treehoppers, this is an exciting science! You can check out some pictures of treehoppers and related insects on my Flickr photostream at: http://www.flickr.com/photos/jasoncryan/