Hunting for ants on Portland

Three people searching the ground or writing in a notebook
Ant hunting on Broadcroft. Photo: Georgie Laing

The Silver-studded Blue has been declining on Portland, so could one of the reasons be anything to do with their host ants?

Ants and butterflies might seem an unlikely combination, but some species of butterfly have a symbiotic relationship with certain ant species and the butterfly will not be found unless the right ants are present.

The ants actually take the newly-hatched caterpillars into their nest and “milk” them for sugars and amino acids. When the caterpillars are ready to pupate, they will do so underground, often in the ants’ nests and the ants continue to tend the chrysalis, even accompanying the newly hatched butterflies to the surface to protect them while they dry out. The female Silver-studded Blue will look for places with colonies of the right species of ant to lay her eggs nearby.

To find the answer as to whether it is lack of ants causing lack of butterflies, four volunteers spent a morning searching for ants on Broadcroft, one of the old quarry sites on Portland.  Clay pots were used to hide sugar lumps and biscuits to tempt them.  Two hours later the pots were checked to see whether the bait had been taken. Success! Most pots did have ants suitable for hosting the caterpillar. So, this looks like the lack of ants is not the problem.

Two butterflies, one blue with black and white markings and the other brown and blue with black, white and orange markings

Silver-studded Blue. Photo: Sharon Towning

The next step will be to return to the site later in the Summer during the butterfly flight period and do some “Timed counts”.  These will cover a wider area than the usual butterfly-monitoring walks to observe any individuals that may have moved off the walk’s route.

A full report of this year’s investigation will appear in the next newsletter.

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