Trip reports


Brian Summerfield

Thursday, 30 July 2020

Both sexes of the Brown Argus (see image) are similar, and they are recognised by their sooty brown colour, absence of blue scales and peripheral orange crescents on all four wings. Its underwings resemble those of the other blues - for this it the family to which it belongs.

They are found in flower-rich limestone and chalk grasslands in southern half of Britain, north to Yorkshire.

The females lay their flat white eggs on the underside of the leaves of rockroses, cranesbills and geraniums and the young caterpillars feed on the underside of the leaf leaving the cuticle intact producing small translucent areas.

The first eggs appear from mid-June to the end of July and next generation lay their eggs from August to early October; this generation of larvae hibernates when small.

The older caterpillars (the 5th instar, after the 4th moult) feed on the upper surface of leaves where they are not hard to find, being green with a pink plimsole line and are usually attended by excited ants that farm them for the honeydew they regularly excrete - a sugary reward for their protection.

When the caterpillar turns into a chrysalis, it emits a pheromone (chemical signal) resembling that of the ant pupae and the ants carry them below ground to safety.

The colony to which my wanderers belong is at Foreness Point, an area that is now being managed to improve the flower rich grassland for the benefit of insects, especially the butterflies and the bumblebees.

Hopes that we might also conserve our ground nesting passerines at this site seemed doomed to failure because of the large numbers of irresponsible dog walkers that also use the site. Long gone are the breeding skylarks and corn buntings.

We hope that wardening and mentoring may help to reduce disturbance to the winter feeding and roosting wading birds. We are only too aware that our visiting purple sandpipers, a rarity in the SE England, have dwindled from flocks of 100 -200 to almost single figures in recent years.

Up to date guidance for dog walkers is published by Thanet DC, check out the link below.

Brian Summerfield