Langstone, Hampshire: A symbiotic relationship means the black ants don’t damage the flowers and protect them from harmful insects
At the end of March, small holes began appearing in the balding patch of lawn at the base of my brick-built raised beds, each surrounded by a ring of excavated earth as fine as sawdust. Dug out by black garden ants (Lasius niger), these are portals to a subterranean network of tunnels and chambers housing a queen and her colony of 4,000-7,000 workers.
While the queen remains below ground, the workers forage widely for food, following scent trails laid down by scouts. During the past two weeks they have found my herbaceous peonies irresistible, scaling the two-foot-tall stems to feast on the sweet nectar secreted by the tightly bound flower buds. Oozing from the nectaries at the base of the bud, viscous globules dot the edge of the sepals.
While the notion that the buds would be stuck closed and unable to flower without the intervention of ants has been disproved, this is still a mutualistic relationship. The ants don’t damage the peony flowers and they defend the plant from attack by harmful, sap-sucking, petal-chewing insects.
As I watch three ants feeding on the same fat bud, I notice that each has adopted a different foraging style. One spirals round the globe from bottom to top, another traverses it in a linear fashion, while the third travels back and forth in a radial, bicycle-spoke pattern.
At times, there are so many of the glossy black-brown insects waiting to access a bud that a queue forms beneath the calyx, but today it is quiet enough that one individual has time to pause and clean its antennae, using its front legs to comb them from root to tip. Grooming is important, as ants use the sensitive hairs on their antennae to communicate, smell food and follow pheromone trails.
The ant/peony relationship is a temporary affair – as soon as the blooms have opened, the ants will abandon the plants in search of new sustenance. While the first petals have only just begun to unfurl, some of the workers have already made the transition from forager to farmer, moving to my broad beans, where they are tending herds of black fly (Aphis fabae), milking the aphids to collect their honeydew.