Another Life: A classic dogfight between butterflies

Butterflies have always known the acre’s hottest spot in spring: a metre or two of garden path, sheltered by hedges and tilted south to warm up nicely in the sun.

Decades ago, when the path was bare and stony, my morning boots would rouse an early peacock butterfly, spread flat to charge up energy for the day. Weeks later in the year, a first red admiral might whirr up, ready for a fight.

Today, grassed over, its sheltering holly grown huge, the path holds leafy perches for a male speckled wood, the dark little butterfly of light and shade. Waiting for a female to fly by, it challenges me at every passing as disturber of its territorial rights.

I have a new garden chair not far away and was sunning myself the other morning when the resident speckled wood engaged in a classic dogfight with an intruding male. They took up the tight, twin, spiralling flight that is classic of their kind and the pair whirred past my nose to vanish among distant bushes.

Ringsend incinerator to supply heat for 30,000 more homes

---

Firefighters battle blaze in Killarney National Park for a third night

---

Ireland ‘tired of being considered laggards’ on climate action – Ryan

---

Such behaviour has its dangers. Jesmond Harding, the Co Kildare lepidopterist, wrote that these aerial battles "often see the butterflies drifting across a glade or road [where they] can be struck by traffic or snatched by spotted flycatchers or dragonflies".

It can also pose unknowns for researchers to research, such as who wins the speckled wood battles.

Simple rule

Predictions of game theory models, it seems, follow “the simple rule ‘resident wins, intruder loses’”. But that can hinge on endurance of whirling flights. “The duration of these encounters” finds one study, “decreases from a mean of 50 seconds and 85 seconds in the first two days to a mean of 10 seconds after a week’s activity.”

Warmer butterflies, says another study, can fly for longer. So those that have been basking in “hot spots” can outfly intruders who’d been up in the air.

A further study proposes that “escalated contests only occurred when both contestants ‘thought’ they were the resident”, an unusual insight into butterfly motivation. None of this, however, spoils the rule: the resident usually wins.

The spiralling battles of the speckled wood are echoed in the lives of male red admirals, long the favourite visitors of an Irish summer. These, too, perch somewhere warm and low to wait for a female, regularly choosing a sheltered glade between our gable and the trees.

Most butterflies may seem to fly randomly in the hope of encountering a mate or finding the next feed of nectar

They assert their territory more militantly, however, flying up to patrol a flight path perhaps half a dozen times before perching again. Meeting an intruding male, they often force a spiralling contest, but one that ends high in the air above the territory, driving the intruder away above the tree-tops.

Away from these ritual behaviours, most butterflies may seem to fly randomly in the hope of encountering a mate or finding the next feed of nectar. Farming scientists, however, find it vitally interesting to know how butterflies navigate, disperse and survive in agricultural landscapes. Researchers at UK's Rothamsted, a venerable centre of agricultural science, have been using "harmonic radar" to track the flights of butterflies.

I leave it to readers to frown over online summaries of this new technology, but it can “extend the range of detection far beyond that of human vision” and is miniaturised enough to stick to an insect thorax with a little wire antenna to send a wavelength signal. A “harmonic” of this signal, reflected back from the transponder, allows its movement to be distinguished from all the radar “clutter” from other objects.

Transponders

It had already been used to track individual flying honeybees and bumblebees over hundreds of metres. Rothamsted researchers caught all the butterflies around their centre in Hertfordshire, shaved their tummies and stuck on transponders that weigh a mere 12mg.

The main species were small tortoiseshell and peacock, with single releases of red admiral, comma and painted lady. From 30 releases, the radar tracks were superimposed over a digitised outline of the fields, recording the intricate loops of foraging. The ability to locate an individual butterfly up to a kilometre away “far exceeds the capabilities of even the most diligent fieldworker”.

Among new conclusions yielded by the project is that butterflies know where they’re going, recognise favourable landscape features and respond to them.

The first peacock near our path this year was sprawled across a dandelion blossom, quite hiding its nectar-rich florets. It was a good reminder of the butterflies’ role in the all-Ireland pollinator plan, nowhere near the contribution of bees but casually worthwhile nonetheless.

This is the final year of records for the all-Ireland butterfly atlas, a project undertaken by the National Biodiversity Data Centre. Sightings can be sent to the centre at biodiversityireland.ie or to butterflyconservation.ie, an excellent website of voluntary fieldwork.