Cocklebur Weevil - Are All Weevils Pests?

The Cocklebur Weevil (Rhodobaenus quinquepunctatus) is a colorful ladybug-mimic. I found this adult at the border of University Woods at East Tennessee State University one day after classes, in a patch of undisturbed native wildflowers and shrubs. Most well-known weevils are pests that leave mass destruction in their wake, sometimes causing famine and changing agriculture forever. It’s easy to fixate on the bad. But what about beneficial weevils?

The larvae of these beautiful cocklebur weevils bore into the stems of many noxious weeds in the sunflower family, eating them from the inside. Weevils are great at eliminating their hosts one by one, so wild plants adjust to their specific weevils. Rough Cocklebur (Xanthium strumarium) is their main host, which produce bunches of painful, spiny fruits that tangle into the hair, clothes, and the flesh of people and other mammals. Ragweeds (like Ambrosia artemisiifolia) are other favorites; the inconspicuous, wind-pollinated plants that give goldenrods a bad name. Goldenrods don’t cause “hay fever.” Their pollen is too big and sticky to become airborne, while ragweeds are chiefly responsible for late-season allergies.

If you’re ever wandering past strips of “overgrown” land in city parks, suburbs, or most farms, notice that there’s usually a much greater, invasive concentration of these native, disturbance-loving plants. Where pesticides are sprayed, cocklebur weevils and all other insect species that help keep the plants at bay are eliminated. This leaves the unrestrained plants to dominate a landscape scarred by people.

It’s nice to know these little guys are on our side, especially if we decide to be on theirs. Insects are key to managing the land. If we assume we’re the best informed, god-like entities to make all decisions, as a single, inherently-flawed species, we’re not gonna make it on this planet for very long.