Grasp the nettle!
Grow nettles to attract butterflies and caterpillars, says Val
ICAN’T believe there’s an R in the month already and that we’re into autumn. However, once the nights become chilly, I will be comforted by memories of this year’s wonderful lockdown spring and some super summer days full of butterflies and bees. The small tortoiseshells – the males and females of which look the same – were everywhere in June, flashing their blue, orange and black wings as they visited flowers in the garden.
The small tortoiseshell is one of my favourite butterflies and you’re likely to see it throughout Britain, in town and country, because it relies on an abundantly common food plant. Like many Latin butterfly names, Aglais urticae provides a clue as to what the small tortoiseshell caterpillars feed on. They feed on nettles, including the common stinging nettle (Urtica dioica) and the small nettle (Urtica urens). The common hop (Humulus lupulus) is also used as a food source on occasions.
In the Cotswolds, caterpillars can be seen from the second half of May until late August. The nettles are always in open, sunny positions. However, if you’re in the South of England there are likely to be three generations. The caterpillars are easy to spot, because the eggs are laid in clusters in a fine silky web. When they begin to grow they stay in a cluster and, when threatened – by a camera lens, for instance – they raise their tails and waggle them about. This doesn’t help with focusing! Their black, white and yellow colouring puts predators off, too. These are warning colours in nature that say, ‘Don’t eat me because I’m poisonous!’
The nettle is thriving, because it’s found in nitrogen-rich soil. Many field margins and low-lying places get nitrogen-rich run off from highly fed fields. This produces an abundant crop of nettles. Car exhaust fumes also produce nitrogen, and the council policy of mowing roadsides verges and leaving the cuttings to rot in situ adds yet more nitrogen. Wildflowers generally need low nutrient levels, which is why you must pick up the cuttings from meadows.
Nettles are the main food plants of three other butterflies. Peacock butterflies have all-black caterpillars that also cluster together on the common nettle, as it’s one of their three food plants. Down the track we saw peacock and small tortoiseshell caterpillars cohabiting. Gregarious peacock caterpillars are usually seen at the end of May and in June, and they have black and white speckles and long black spines. This peacock, which is spreading northwards, hibernates as an adult in early September and re-emerges in spring, so it’s one of the first butterflies on the wing. The males and females look the same, with four large ‘eyes’, but the females are larger.
The comma butterfly also uses nettles, although it has wide range of food plants that include hop, elm, currants and willow. This richly coloured orange and black butterfly has two flight periods, May and early August. It’s the white comma mark on the underwing that gives it its name. The black caterpillars are banded in orange-brown with a white splash that tricks the eye into thinking it’s a piece of bird muck. I’ve seen them on gooseberry bushes, although their most widely used food plant is nettle.
It’s been a good year here for peacocks, commas and small tortoiseshells, but, sadly, we didn’t see many painted lady butterflies. These fast-flying migrants are strong flyers, which is a good thing because they make their way, breeding as they go, from the desert fringes of North Africa, the Middle East and central Asia. Last year was said to be a bumper year, although we didn’t get many here. Their caterpillars, which are dark with white spines, feed singly and can be seen between May and October. Although the caterpillars use nettles, they seem to prefer thistles in my neck of the woods.