The small tortoiseshell butterfly

The small tortoiseshell (Aglais urticae) is one of Britain's most beloved butterflies, and also one of the more common, being quite a widespread species. 

There are only a few species of British butterfly that we see in early spring and generally the earliest individuals seen each year are those that survive the winter by hibernating in their adult form. One butterfly which regularly over-winters in Britain is the small tortoiseshell.

The small tortoiseshell is widespread over the whole of the UK and it has two broods every year, the first brood of eggs is laid in May by adults which have hibernated through the winter.  Adults from this first batch of eggs begin flying during July and their eggs ensure a second population of adult butterflies in late summer. It is only the adults from this second brood which will hibernate over winter.

In recent years there has been a decline in the number of small tortoiseshell butterflies and at the moment scientists are still unsure as to the exact cause. One suggestion is that a parasitic fly, prevalent on the continent, is attacking the larvae of the small tortoiseshell, this theory ties in with the fact that its decline has been most noticeable in the southern half of the UK.

Attracting small tortoiseshells into the garden

Growing flowers in our gardens is one thing but it takes a really environmentally-conscious gardener to provide the small tortoiseshell with its most desired plant, the stinging nettle which is the food-plant of its caterpillars. If you choose to grow nettles in your garden to support butterflies then a sunny spot is best.

So strong is the association with nettles that the butterfly’s scientific name, Aglais urticae, is partly derived from urtica meaning stinging nettle. Aglaia was one of the three Graces, a daughter of Zeus admired for her beauty, and the choice of this name reflects the elegance of the small tortoiseshell. 

In return for providing a garden full of nectar-rich flowers, on which these butterflies can feed, we get the opportunity to watch one of Britain's most colourful and attractive butterflies.

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Small tortoiseshell butterfly lifecycle

Egg laying time

The small tortoiseshell butterfly who emerges from hibernation lays its eggs in May, and this brood goes on to lay a second generation in July. It is the second generation which will overwinter. The small tortoiseshell eggs are like green beads laid in clusters on the underside of nettles.

Small tortoiseshell butterfly caterpillars

The larva of small tortoiseshell butterflies will emerge in May or July, depending on which generation they are, after about 9 days. As the eggs are laid in clusters you will often see a lot of caterpillars clustered together (the collective noun is an 'army of caterpillars').  The caterpillars build webs which will trail from plant to plant as they spread. newly hatched caterpillars have a pale green body and black head, and the body will darken as they age. By the final instar (skin) they will have a spiky black body with yellow speckling on the side.

Small tortoiseshell butterfly chrysalis

The small tortoiseshell forms a pupa that resembles a brown, crinkly leaf that hangs hangs from plant stems. They pupate for up to four weeks, depending on temperature.

Transformation into butterflies

The adult (imago) small tortoiseshell is approximately two inches across and has beautiful orange, yellow and black markings on its upper wing, bordered by blue spots. The lower wing is dark brown and serves as camouflage while the butterfly is asleep. 

Male and female small tortoiseshell butterflies

Male and female small tortoiseshells indistinguishable in appearance, but can often be told apart by their behaviour. Males will sit near a foodplant with their wings open, waiting for a female to enter the territory. When she flies close he will follow her through the air performing an unusual mating dance where he drums his antennae on her wings. They can often be spotted basking together to recuperate.

Small tortoiseshell butterfly and hibernation

When a small tortoiseshell butterfly looks for a safe place to hibernate, the small tortoiseshell will often hide away in an outhouse or shed, so our gardens offer great refuges for them through the winter. Upon emerging in spring, their priority is to find nectar so a well-stocked flower garden is their saviour again. 

On warm days the butterflies will sometimes wake up in winter, meaning you could well spot a small tortoiseshell on the wing in December or January.

Most butterflies hibernate as caterpillars or pupa, but other butterfly species which hibernate in adult form include peacock butterflies, comma butterflies and the brimstone butterfly. The red admiral does try to, but doesn't usually survive British winters.

Small tortoiseshell butterfly lifespan

The lifespan of a small tortoiseshell can vary depending on generation. The first brood will live for just a couple of months, while their children (who hatch in July and early August) will go into hibernation in September and reawaken the following spring, giving them a lifespan of around nine months.

Visit our garden wildlife section for more, including the best plants for a wildlife-friendly garden and butterfly photography tips

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