Two Westbury Grassland Butterflies of the Week 3rd June 2020



Meadow brown: The Meadow brown is probably our commonest butterfly and is on the wing from the beginning of June through to September or even October if the weather is kind. It is quite a large brown butterfly being a bit smaller than a large white. The females are larger than the males and have conspicuous orange patches on the forewings whereas the males look generally darker and have an area of dark scent scales on the upper surface of their forewings that produce pheromones that encourage the females to mate. They can be abundant in grassland that is not too heavily grazed as well as along roadside verges, the edges of woodland rides and anywhere else with a good mix of grasses maybe up to 50cm high. Eggs are laid singly amongst the grasses and may even be scattered. The young caterpillars feed on the finer grass species like fescues and the older caterpillars move on to more robust species like cock’s foot and wood false brome. They overwinter as caterpillars hidden deep in suitable grass tussocks. During the following spring they start feeding again and pupate in late April and onwards depending on the size of caterpillar they overwintered as. Males will fly quite long distances seeking out unmated females that are ‘seduced’ by showers of pheromones. Mating can last for up to an hour when the pair can be seen resting amongst grasses. If disturbed the female can fly with male still attached to a new resting spot. The female soon begins egg laying and it is these eggs that produce the caterpillars that will spend the winter in a grass tussock. There is just one generation each year.

Photos Tina Westcott   Peter Bright



Small heath: This little butterfly is a ‘brown’ like its relative the meadow brown but is only the size of a common blue. Its caterpillars feed on fine grasses like fescues that abound in dry, shallow soiled, unimproved short sward grassland like that found on the top of Mendip. Westbury Beacon, Cook’s Field and Deerleap are good habitat. It is hardly surprising that it has barely appeared in Westbury gardens in our regular weekly recordings. It overwinters as a caterpillar in various stages of maturity depending on when winter comes. The largest of these caterpillars will pupate in early spring to appear as the first small heaths of the year in early May. The smaller caterpillars will take longer to grow and then pupate to produce the later butterflies of this first brood. These adults then mate to produce eggs leading to a second generation on the wing in late July and August. Their eggs will become the caterpillars that will over winter to emerge in the following spring. This small butterfly, itself, shows orange when it flies showing the orange upper surfaces of its wings but when it settles – always with its wings closed, all you see is the grey brown underside of the hind wing and a small flash of orange from the underside of the forewing. This frequently disappears as it folds its forewings further and it can almost disappear against the browns and greys of its preferred dry grassy habitat. In can increase the effectiveness of this camouflage by holding its wings at such an angle that they do not cast a shadow.

Photos   Oliver Halls   Peter Bright

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