There are about 1,850 species of native plants in the floristically diverse state of Ohio, and two of those natives are ragweeds (there is arguably a third, but it is too scarce to warrant inclusion). This pair, the common and giant ragweeds, probably rank near the top of the despicable plant list. The ragweeds have tiny, roughened windborne pollen, and it is this pollen blowing on the wind that is a major source of hay fever, the bane of many who venture outdoors.
But as with all native plants insofar as I have become aware, ragweeds have their value, if not to us. As these jolly green giants have been around for a long time, a whole platoon of insects has co-evolved to exploit the plants. Thus, ragweed stands spawn a fascinating ladder of biodiversity. I'll probably win no friends by going to bat for these botanical underdogs, but it is worthwhile to note the value of even the most despised organisms.
Giant ragweed often forms massive stands, especially in moist soil of low-lying fields, river floodplains, wetland margins, etc. Individual plants can reach Jack-in-the-beanstalk proportions, towering to 15 feet in height. Such ragweed groves are typically shunned by all who encounter them.
Like some other amazing borers, this one spends much of its life cycle burrowing through the stems of plants, and Dectes texanus is especially fond of ragweeds. Perhaps it could be dubbed the "ragweed borer".
Festive fruit flies are utterly dependent upon giant ragweed. They lay their eggs in the flower clusters - some blooms of the ragweed are in the upper lefthand corner of the photo - and the larvae ride out the winter within the seeds. Come late summer, and the astonishing adults are capering about the ragweed foliage, engaging in eccentric courtship displays. If there is one compelling reason to inspect giant ragweed stands, it is because of the possibility of seeing this marvelous fly.
The genus of ragweeds is Ambrosia, and that translates to "food of the gods". That may be overstating the case a bit, but festive fruit flies sure like the stuff.