Summer Azure (Celastrina neglecta)

In this guide

1. Description and identification
2. Life cycle: egg, caterpillar, chrysalis and adult
3. Where the summer azure lives
4. Host plants and diet
5. Behavior: flight, puddling and ant partnerships
6. Similar butterflies and how to tell them apart
7. Quick facts
8. Did you know?
9. Pictures
10. Frequently asked questions

Description and identification

The summer azure is a small pale blue butterfly of the gossamer-winged family (Lycaenidae), the huge, worldwide family of blues, coppers and hairstreaks whose members are nearly all small and delicate. It belongs to the azures, a group of North American Celastrina species that look so alike that this one was treated for most of the twentieth century as nothing more than the summer generation of the spring azure. It is now recognised as a separate species with its own hosts and its own flight period.

Adult butterfly

• Wingspan: 0.9–1.2 in (23–30 mm), with the largest late-summer females occasionally a little bigger.
• Male upperside: pale sky blue overlaid with a heavy dusting of white scales, so that a fresh male looks frosted or powdered rather than solidly coloured. A thin dark line runs along the outer margin, and the fringes are white.
• Female upperside: much whiter. Most females are white across the middle of the wing with blue confined to the base, and they carry a distinct dark grey to black band along the leading edge and outer corner of the forewing. Late-brood females are the whitest butterflies of the year.
• Underside: chalky white to very pale grey in both sexes, marked with a scatter of small grey dots and a faint broken line of pale smudges near the margin. There is no orange anywhere on the wing and no tail.
• Body: small and slender, blue-grey above and white below, with black-and-white ringed antennae and white-ringed eyes.

Wear changes the butterfly quickly. Within a week the white scaling rubs off the male's upperside and the blue looks plainer and darker, while the underside of an old individual loses its dots and fades almost to plain cream.

How to identify a summer azure in the field

Start with the calendar, because it does more work than any wing mark. An azure flying in eastern North America after the middle of June is almost always this species; one flying in March or April is the spring azure. Then look at the underside: the summer azure is strikingly white and lightly marked, where the spring azure is greyer with bolder dark blotches. Watch for a small pale butterfly that flutters weakly around shrub flowers, along woodland edges, gravel roads and damp patches, landing often and always closing its wings the moment it settles.

Life cycle: egg, caterpillar, chrysalis and adult

The summer azure runs through two or three complete generations a year across most of its range, each one taking about a month from egg to adult, and it passes the winter as a pupa. The same four stages are set out for butterflies in general in our guide to the life cycle of a butterfly.

Eggs

Females lay singly, tucking each egg among the unopened flower buds of the host shrub. The egg is a flattened pale turquoise to greenish-white disc less than 0.5 mm across, its surface cut into a fine honeycomb of ridges, and it is almost impossible to see without a lens. A female spends much of the day working over flowering shrubs, testing each cluster with her forelegs, and she seldom leaves more than one egg on a head of flowers. Hatching takes three to five days.

Caterpillar

The caterpillar is a short, flattened, slug-shaped larva with the head tucked out of sight beneath the front segment. Colour is very variable — pale green, whitish green, yellowish, pink or dull rose — and most individuals carry a darker band down the middle of the back, edged by pale maroon and cream, with oblique dashes along the sides. It reaches about 0.4 in (10 mm).

Larvae feed on flower buds, open flowers and developing fruit rather than on foliage, which is why the whole life cycle is tied to the flowering season of the shrub. Like most members of the family, the larva has a honey gland on its back that produces a sugary secretion, and it is regularly attended by ants, which take the sugar and in return drive off parasitic wasps and small predators. The larva matches whatever it is eating closely enough that most are found only by looking for the ants.

Chrysalis

The full-grown larva leaves the shrub and forms a chrysalis in the litter below, sometimes in a curled dead leaf or just under the soil surface. The pupa is a small, smooth, light brown object speckled with darker brown and black, and it passes for a fragment of dead leaf. Pupae of the early broods produce adults within one to two weeks; those formed at the end of the season stay put and overwinter, which makes the pupa the only stage that survives the cold months.

Adult butterfly

Adults live only about one to two weeks. They emerge in waves, starting in late May or June once the spring azures have gone, with further flights through July, August and into September; in the south of the range a few individuals are still flying in October. Because the broods overlap, fresh and worn individuals are usually on the wing at the same time.

Where the summer azure lives

The summer azure is a butterfly of eastern and central North America. It occurs from Nova Scotia and southern Quebec west through Ontario to the prairie provinces, and south through New England and the Great Lakes states to Florida and the Gulf coast, reaching west to the eastern Rockies and into eastern Colorado and central Texas. It is common to abundant through most of that area and is one of the small butterflies most likely to be seen in a suburban yard.

Habitat is wherever flowering shrubs grow in partial sun: woodland edges and clearings, brushy stream valleys, roadsides and gravel tracks, old fields, marsh edges, powerline cuts, hedgerows, parks and gardens. The species does not need undisturbed habitat and often does best along the untidy margins between woodland and open ground, where dogwood and viburnum flower year after year.

Individual butterflies wander freely, and males in particular drift along an edge for hundreds of yards in a day, so the species turns up well away from any breeding shrub. It does not migrate, and the overwintering pupae stay where the larvae fell.

Host plants and diet

Caterpillar host plants. The summer azure uses a wide range of flowering shrubs and herbs, and the defining feature of its host plants is simply that they are in bud when the female is flying. Gray dogwood (Cornus racemosa) and the other shrubby dogwoods are the mainstay through much of the range, together with New Jersey tea (Ceanothus americanus), meadowsweet and steeplebush (Spiraea), viburnums, sumacs and, in places, black snakeroot and wingstem. Because the larvae eat flowers rather than leaves, a plant is only useful for the few weeks it is in bloom, and successive broods move from one shrub species to the next as the summer goes on.

Adult diet. Adults take nectar from small flat-topped flowers — dogbane, milkweeds, meadowsweet, white sweet clover, goldenrod and the host shrubs themselves — and they are not choosy, as our guide to what butterflies eat explains for the family as a whole. Males also gather at damp sand, mud and gravel to drink dissolved salts, and both sexes will feed at sap runs, animal droppings and rotting fruit.

Behavior: flight, puddling and ant partnerships

Flight. The flight is quick but weak-looking, a low fluttering zigzag a foot or two above the ground that rises and falls as the butterfly drifts along an edge. Summer azures do not fly far in a straight line, they stop frequently, and they almost always settle with the wings closed, which is why photographs of the blue upperside are so much rarer than photographs of the white underside.

Puddling. On warm days males collect on damp gravel, on the wet margin of a puddle or at a patch of urine-soaked sand, sometimes several at a time, and sit with their probosces down for long periods. They are drinking sodium and other minerals, which are passed to the female in the sperm packet at mating and end up in the eggs. Females puddle far less often.

Ant partnership. The larval honey gland buys protection. Ants of several common genera patrol the flower heads where azure larvae feed, milk the gland for sugar and attack the parasitic wasps that would otherwise lay eggs in the caterpillar. The relationship is loose rather than obligatory: azure larvae survive without ants, but they survive better with them. Many gossamer-winged butterflies run the same arrangement, and in a few of them, such as the European holly blue group and the large blues, it has become far more elaborate.

Courtship and roosting. Males patrol shrub edges through the middle of the day, investigating anything small and pale; courtship is brief, and pairs sit head to tail on a leaf or flower head for an hour or more. At dusk and in dull weather adults roost head-down on grass stems and low twigs with the wings closed, where the chalky underside makes them look like a dead flower.

Similar butterflies and how to tell them apart

Quick facts

Did you know?

• For most of the last century this butterfly had no name of its own. It was treated as the summer brood of the spring azure, and only careful work on flight periods, host plants and genitalia in recent decades separated the azures into several species.
• The caterpillars are flower eaters. Feeding on buds and blossom instead of leaves ties each brood to a plant that is in bloom at that moment, so the butterfly effectively changes host species as the summer advances.
• The white frosting on a male is scale dust, not colour. It rubs off with use, so the same butterfly looks paler on the day it emerges than it does a week later.
• Ants can be used to find the caterpillars. A line of ants running up a dogwood in flower is worth following, because they are often tending an azure larva hidden among the buds.
• Puddling males are after salt, not water. The sodium they collect from damp gravel is transferred to the female at mating and invested in her eggs.
• It is one of the family's quiet success stories. Lycaenidae is one of the largest butterfly families in the world, and the summer azure is among its most adaptable members, thriving along the untidy edges of farmland and suburbs where showier butterflies have disappeared.

In summary

The summer azure is the small, chalky-white and pale blue butterfly that takes over eastern North American woodland edges once the spring azures are finished. Males are frosted blue above, females largely white with a dark forewing border, and both are nearly white beneath with fine grey dots and no tails or orange marks. Its eggs go into flower buds, its slug-shaped caterpillars eat blossom under an escort of ants, and its speckled brown pupa carries the species through the winter in the leaf litter. If you see an azure after midsummer, you have almost certainly found this one.

Summer Azure butterfly pictures

Frequently asked questions about the summer azure butterfly

What does a summer azure caterpillar look like?

It is a short, flattened, slug-shaped larva about two fifths of an inch long, with the head hidden under the front segment. Colour varies from pale green and whitish green to yellow, pink or dull rose, and most have a darker band down the back edged with maroon and cream, plus oblique dashes along the sides.

How can you tell a male summer azure from a female?

Look at the upperside. Males are pale sky blue heavily dusted with white scales and edged by a thin dark line. Females are much whiter, with blue confined to the wing bases and a distinct dark grey or black band along the leading edge and tip of the forewing. The undersides of both sexes look the same.

What butterfly family does the summer azure belong to?

It belongs to Lycaenidae, the gossamer-winged butterflies, which also contains the blues, coppers, hairstreaks and harvesters. Despite the small size of its members, Lycaenidae is one of the largest butterfly families in the world, with several thousand species, and many of them have caterpillars that form partnerships with ants.

How does the summer azure chrysalis avoid predators?

The pupa is small, smooth and light brown with darker brown and black speckling, and it is formed in the leaf litter under the host shrub, sometimes inside a curled dead leaf or just below the soil surface. The combination of colour, pattern and position makes it read as a scrap of dead vegetation.

What do summer azure caterpillars eat?

They eat flower buds, open flowers and developing fruit rather than leaves. The main plants are gray dogwood and other shrubby dogwoods, New Jersey tea, meadowsweet and steeplebush, viburnum and sumac. Because they depend on blossom, each brood uses whichever shrub happens to be in bud at that point in the summer.

How do you tell a summer azure from a spring azure?

The flight period is the most reliable clue: spring azures fly in one brood from March to May, summer azures from late May or June into September. The summer azure is also whiter, with a chalky, lightly dotted underside, while the spring azure has a greyer underside with heavier dark blotches.

Why is the summer azure chrysalis hard to find?

It is under a quarter of an inch long, it is coloured and speckled like dead leaf tissue, and it is not attached to the foodplant at all. The caterpillar crawls off the shrub before pupating, so the chrysalis ends up loose in the litter on the ground where almost nobody looks for it.

Do summer azure caterpillars really work with ants?

Yes. The larva has a gland on its back that releases a sugary secretion, and ants of several common genera feed on it while patrolling the flower heads. In exchange the ants drive off parasitic wasps and small predators. The partnership is optional rather than obligatory, but larvae guarded by ants survive noticeably better.

When and where can I see summer azures?

From late May or June through September across eastern and central North America, on warm sunny days. Look along woodland edges and clearings, brushy stream valleys, roadsides, old fields and garden borders, especially where dogwood, viburnum or meadowsweet is flowering, and at damp gravel where males gather to drink minerals.

Is the summer azure harmful to gardens or to people?

No. Adults cannot bite or sting, the caterpillars have no irritating hairs, and neither stage is toxic. Larvae eat a small number of flower buds on shrubs such as dogwood and New Jersey tea and never occur in numbers that damage a plant, while the adults are useful pollinators of small summer flowers.