It was a warm spring-day in mid-April, and there was nary a cloud in the sky. A nearby meadow was dotted with patches of dazzling blue. The season’s first bachelor’s buttons (Centauria cyanis) were in bloom. A native of the Mediterranean coast of Europe, bachelor’s buttons are also known as cornflowers. In southern Europe, where wheat is also called “corn”, these lovely flowers grow wild amid the grain fields. Here in the Southeast, they are commonly found in pastures and along roadsides, where they are considered weeds.
The bachelor’s button plants were the beneficiaries of the efforts of two different insects, one quite expected, the other surprising. The former was a honey bee (Apis mellifera), photographed above, pollinating the flowers in a quest to produce honey for her hive. (A more stunning professional photograph of a bee pollinating a bachelor’s button can be viewed here.) The unlikely ally was the fire ant, Solenopsis invicta.
The fire ants themselves were long gone. There was not a single active ant mound rising from anywhere in the field. Perhaps they were lying low so early in the season, or perhaps the landowner had poisoned all the mounds last autumn. But there were traces of mounds left behind — patches of bare, dry earth, mostly or entirely leveled. A dense ring of the healthiest, tallest bachelor button flowers encircled each former fire ant mound site like a halo. Elsewhere in the field, the same flowers were sparser, farther apart, and shorter.
What was it about the mound locations that made them so favorable to flower growth? Researchers have identified several possible explanations. Fire ants aerate the soil in the process of building their mounds. As a result, plant roots are more easily able to obtain oxygen, and rainfall percolates more easily into the soil, too. Fire ant mounts are also more fertile than surrounding soils: they were comparatively higher in the nutrients potassium and phosphorus, and lower in pH (more acidic). It is a mystery, quite tempting to solve through scientific experimentation and analysis, which factor or factors was responsible for this particular bumper crop of flowers.
A few former fire ant mounds are simply bare spaces scattered in a field. But now imagine that field over decades, with new mound sites appearing every year. Over time, the entire field might be reworked by the industrious ants, enhancing the soil fertility and structure to benefit various plants and maybe even hungry cows. It is comforting somehow to know that even fire ants, the bane of gardeners and bare-footed outdoors-folk throughout the Southeast, can have their benefits, too.