Spring Azure (Celastrina ladon)

In this guide

1. Description and identification
2. Life cycle: egg, caterpillar, chrysalis and adult
3. Where the spring 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 spring azure is a small blue butterfly of the gossamer-winged family (Lycaenidae), the worldwide family of blues, coppers and hairstreaks. It belongs to Celastrina, a group of North American azures that resemble one another so closely that they were long lumped together, and for much of the twentieth century this butterfly was also treated as a New World race of the Eurasian holly blue. Today Celastrina ladon is recognised as a species in its own right: the early one, with a single short brood in spring and its own set of host plants.

Adult butterfly

• Wingspan: 0.75–1.25 in (19–32 mm).
• Male upperside: bright violet-blue and evenly coloured, with only a thin dark line along the outer margin and white fringes.
• Female upperside: blue as well, but noticeably darker and duller, with a broad blackish-grey border that widens across the tip and outer edge of the forewing and often a dark smudge along the hindwing margin.
• Underside: pale grey to greyish-white in both sexes, scattered with small black dots and short dashes and finished with a row of faint darker smudges inside the margin. Some individuals, especially early-emerging ones, show a broad dark grey band across the hindwing.
• Tails and spots: none. There is no tail at the rear of the hindwing and no orange anywhere on the butterfly.
• Body: small and slender, blue-grey above and whitish below, with black-and-white ringed antennae and pale-ringed eyes.

How to identify a spring azure in the field

The date is half the answer. A small blue butterfly flying in eastern North America in late March, April or early May, often before the woodland trees are in leaf, is almost certainly this species; the same butterfly seen in July is the summer azure. Watch for a weak, fluttery, low flight around flowering shrubs, woodland edges, forest tracks and damp gravel, and for the habit of landing frequently and closing the wings at once. Then check the underside: pale grey, finely dotted with black, no tails, no orange.

Life cycle: egg, caterpillar, chrysalis and adult

The spring azure runs one generation a year. Adults fly for a few weeks in spring, the larvae grow while the host shrubs are in flower, and the pupa formed in early summer sits out the rest of the year. The general pattern is set out in our guide to the life cycle of a butterfly.

Eggs

Females lay their eggs singly, pushing each one down among the unopened flower buds of the host shrub rather than placing it on a leaf. The egg is a flattened pale green to greenish-white disc under half a millimetre across, its surface sculpted into a fine honeycomb of ridges, and it is effectively invisible without a lens. She tests bud clusters with her forelegs and rarely leaves more than one egg on a head of flowers. Hatching takes four to eight days.

Caterpillar

The caterpillar does not look like a caterpillar at all. It is flattened, broad and slug-shaped, with the head hidden beneath the front segment, and it reaches only about 0.4 in (10 mm). Colour varies with what it is eating: green, whitish-green, yellowish, pink or rose, usually with subtle moss-green or maroon marks and a darker line down the middle of the back. It feeds on flower buds, open blossom and developing fruit, not on foliage, which is why the whole larval stage is squeezed into the few weeks a shrub is in bloom.

A gland on the larva's back produces a sugary secretion, and ants feed on it while patrolling the flower heads. In exchange the ants drive off parasitic wasps and small predators, an arrangement common throughout this family.

Chrysalis

The full-grown larva leaves the flowers and pupates low down — in leaf litter under the shrub, in a curled dead leaf or just below the soil surface — rather than on the upper surface of a leaf, where it would be exposed for months. The chrysalis is a small, smooth, rounded object, beige to light brown or grey with darker blotches and speckles, and it passes for a fragment of dead leaf. This is the stage that overwinters: the pupa formed in June may not release its butterfly until the following March or April.

Adult butterfly

Adults are short-lived, surviving roughly a week and occasionally a fortnight, which is brief even by butterfly standards — our guide to how long butterflies live sets that against other species. Emergence is spread over several weeks, so the population flies from March in the south to early June in the north, even though each butterfly is on the wing for only a few days of it.

Where the spring azure lives

The spring azure in the strict sense is a butterfly of eastern North America. It occurs from Nova Scotia, southern Quebec and Ontario south through New England, the Appalachians and the Great Lakes states to Georgia and the Gulf states, and west to the edge of the Great Plains. Azures as a whole go much further: related Celastrina species reach Alaska, run down the Rocky Mountains and the Pacific coast, and continue through Mexico and Central America into the mountains of Colombia. The old accounts that give the spring azure a range from the Alaskan tundra to Colombia were describing that whole complex, before it was split into separate species.

Its habitat is deciduous woodland and its margins: open woods, clearings and light gaps, the edges of forest tracks and roads, second growth, brushy stream valleys, wooded swamps and freshwater marsh edges, and old fields that back onto trees. It needs shrubs and small trees that flower early, so it is most abundant where dogwood, viburnum and blueberry grow along a sunny woodland edge. Suburban parks and large gardens with native flowering shrubs suit it well.

The butterfly does not migrate. Adults wander a few hundred yards along an edge, and the overwintering pupae stay in the litter where the caterpillars dropped, so colonies are tied closely to the shrubs that feed them.

Host plants and diet

Caterpillar host plants. The defining feature of spring azure host plants is timing: the shrub must be in bud while the butterfly is flying. Flowering dogwood (Cornus florida) is the classic host through much of the range, along with viburnums, New Jersey tea (Ceanothus americanus), blueberry and meadowsweet (Spiraea). Western and later-flying members of the azure group use other plants entirely — Collinsia, for instance, belongs to the western echo azure rather than to this species, and black cohosh belongs to the Appalachian azure. Because the larvae eat blossom, a plant is only useful for the two or three weeks it is in flower.

Adult diet. Adults take nectar from whatever is open that early: spicebush, wild plum and cherry, blueberry, willow catkins, violets, dandelion, strawberry, redbud, blackberry and the host shrubs themselves. Later-blooming flowers such as dogbane, privet and common milkweed are visited by the azures that fly in summer rather than by this one. Males also gather at damp gravel, mud and puddle margins to drink dissolved minerals, and both sexes will feed at sap and at bird droppings, which is more nourishing than it sounds.

Behavior: flight, puddling and ant partnerships

Flight. The flight is quick but looks weak: a low, fluttering zigzag a foot or two above the ground, drifting along a woodland edge or a track and dropping abruptly onto a flower or a patch of damp grit. Spring azures rarely fly far in a straight line and almost always settle with the wings closed, which is why photographs of the grey underside far outnumber photographs of the blue.

When they are active. They are strictly day-flying and need sun. Activity builds through the morning, peaks in the warm middle hours and continues into the late afternoon, and the butterflies drop into cover at dusk or when cloud crosses the sun.

Puddling. On warm days males collect on damp gravel, mud and the wet margins of puddles, sometimes several together, and stand with the proboscis down for long periods. They are taking sodium and other minerals, which are passed to the female in the sperm packet at mating and end up invested in the eggs. Females puddle far less often.

Ant partnership. The larval honey gland buys protection. Ants milk the gland for sugar and, while they are there, attack the parasitic wasps and flies that would otherwise lay eggs in the caterpillar. The relationship is loose rather than obligatory — azure larvae survive without ants but survive better with them —.

Courtship and roosting. Males patrol shrubby edges and clearings through the middle of the day, investigating anything small and pale that passes. Mated pairs sit head to tail on a twig for an hour or more. At dusk, and in dull weather, adults roost head-down on grass stems and low twigs with the wings shut, where the pale grey underside makes them look like a dead flower head.

Similar butterflies and how to tell them apart

Quick facts

Did you know?

• It is often the first butterfly of the year, on the wing in much of eastern North America before the woodland canopy has closed.
• The azures have been split and re-split. What was once a single species stretching across the northern hemisphere is now several, separated by flight period, host plant and fine structural differences rather than by wing pattern.
• The caterpillars eat flowers. Feeding on buds and blossom rather than foliage ties the larva to a shrub that is blooming at exactly the right moment, and it is why the butterfly has only one generation a year.
• The pupa does almost all the waiting. A spring azure spends a week or two as an egg, three or four weeks as a caterpillar, a few days as an adult, and the remaining ten months of its life as a chrysalis in the leaf litter.
• Puddling males are after salt, not water. The sodium they collect from damp gravel is handed to the female at mating and ends up in her eggs.

In summary

The spring azure is the small violet-blue butterfly that opens the season along eastern North American woodland edges, no more than an inch and a quarter across, with a pale grey, finely dotted underside and no tails or orange marks. Males are evenly blue, females darker with a broad grey-black forewing border. Its eggs go into flower buds, its slug-shaped caterpillar eats blossom under the escort of ants, and its speckled brown pupa lies in the leaf litter for most of the year. An azure met in early spring is this one; one met after midsummer is almost certainly the summer azure.

Spring Azure butterfly pictures

Frequently asked questions about the spring azure butterfly

How can you identify a female spring azure butterfly?

Look at the upperside. A female is blue like the male but darker and duller, and she carries a broad blackish-grey border that widens across the tip and outer edge of the forewing, often with a dark smudge along the hindwing margin as well. Males are evenly violet-blue with only a thin dark line at the margin.

What does a spring azure caterpillar look like?

It is flattened, broad and slug-shaped, with the head hidden under the front segment, and it grows to only about two fifths of an inch. Colour varies with its food and can be green, whitish-green, yellowish, pink or rose, usually with faint moss-green or maroon marks and a darker line down the back.

What is the wingspan of a spring azure butterfly?

About 0.75 to 1.25 inches, or 19 to 32 millimetres, which makes it one of the smallest butterflies most people notice. Older accounts that give a figure approaching 1.8 inches are too large for this species; anything much over an inch and a quarter is worth a second look.

When are spring azure butterflies active?

They fly by day and need sunshine. Activity builds through the morning, peaks in the warm middle hours and carries on into the late afternoon, and the butterflies drop into cover at dusk or as soon as cloud crosses the sun. The flight season itself runs from March to early June, depending on latitude.

Why are ants often found with spring azure caterpillars?

The caterpillar has a gland on its back that releases a sugary secretion, and ants feed on it. While they are there they attack the parasitic wasps and flies that would otherwise lay eggs in the larva. The partnership is optional rather than obligatory, but guarded caterpillars survive noticeably better.

Where does the spring azure form its chrysalis?

The full-grown caterpillar leaves the flowers and pupates low down, in the leaf litter beneath the shrub, inside a curled dead leaf or just below the soil surface. The pupa is beige to light brown or grey with darker blotches, and it stays there through the summer, autumn and winter before the adult emerges in spring.

What is the geographic range of the spring azure butterfly?

The spring azure proper is an eastern North American butterfly, found from Nova Scotia, Quebec and Ontario south to Georgia and the Gulf states and west to the Great Plains. The wider azure group extends much further, from Alaska down the Rockies and through Central America to the mountains of Colombia, but those are separate species.

What do spring azure caterpillars eat?

Flower buds, open blossom and developing fruit rather than leaves. The main plants are flowering dogwood, viburnums, New Jersey tea, blueberry and meadowsweet. Because the larvae depend on blossom, they can only grow while the host shrub is in flower, which limits the butterfly to a single brood each year.

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

The date does most of the work. Spring azures fly in one brood from March to early June; summer azures fly from late May or June into September. The summer azure is also whiter, with a chalky, lightly dotted underside and heavy white frosting on the male's upperside, while the spring azure is greyer and more boldly marked beneath.

Are spring azure butterflies harmful to gardens or people?

No. The 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 viburnum and never appear in numbers that damage a plant, while the adults pollinate early spring flowers at a time when few other insects are flying.