Blue Metalmark (Lasaia sula)
Barely an inch across and the only blue metalmark in the United States, this butterfly sits flat on a sunlit leaf in the thorn forest of the Lower Rio Grande Valley with its wings spread like a tiny sheet of hammered turquoise. The male's colour is not pigment at all but light bouncing off ridged scales, and the female, on the same bush, is plain chequered grey.
By Dr. James WatuwaPublished December 4, 2018Updated September 16, 2026✓ Reviewed by Poppy Glendening
In this guide
Description and identification
The blue metalmark belongs to the metalmark family, a huge, mostly tropical group of small butterflies named for the metallic-looking spots and streaks that many of them carry on the wings. Metalmarks are easy to recognise as a family once you know two things: the males walk on only four legs, because the front pair is reduced to a small brush, while females use all six; and the antennae are unusually long, black with fine white rings and a neat club. Lasaia sula is the only metalmark in the United States with a genuinely blue male.
Adult butterfly
- Wingspan: 0.9–1.3 in (22–32 mm). Small, and it looks smaller still because it holds the wings flat rather than upright.
- Male upperside: the whole surface of all four wings is a shimmering blue-green, somewhere between turquoise and steel blue, crossed by rows of small black dots and short dashes. The outer edges are bordered in light to dark grey.
- Female upperside: no blue at all. The ground is grey to grey-brown, arranged in a chequered pattern of pale and dark bands with the same rows of black spots, so a female looks like a miniature chequered skipper until you see the antennae.
- Underside: alike in both sexes, greyish brown with the chequering repeated and the black spots showing through. A butterfly with its wings closed cannot be sexed in the field.
- Body and antennae: small, furry, grey-brown body; long black antennae ringed with white.
The male's blue is structural, not pigmented. Microscopic ridges on the wing scales interfere with light and throw back a narrow band of it, which is why the colour slides from green to violet-blue as the butterfly turns, and why a worn individual with damaged scales looks dull grey. The rest of the pattern, the black chequering and grey borders, is ordinary pigment and does not change with angle.
How to identify a blue metalmark in the field
Look at the posture first. A blue metalmark almost always sits with the wings pressed fully open and flat against a leaf, a stem or bare ground, facing the sun. The small blue butterflies of the family Lycaenidae that share its habitat do the opposite: they settle with the wings closed over the back and show only the pale, spotted underside. Then check the colour. The blue of a metalmark is metallic, greenish and finely chequered with black, whereas a lycaenid blue is soft, powdery and lavender-toned. Finally, look for the long ringed antennae and for the way the butterfly flies, low and buzzy, in short bursts of a few feet before dropping back onto a perch.
Life cycle: egg, caterpillar, chrysalis and adult
The blue metalmark produces several overlapping broods a year in its warm subtropical range, so eggs, larvae, pupae and adults can all be found in the same month. The early stages are among the least documented of any butterfly in the United States, and much of what follows comes from the family as a whole as much as from this one species.
Eggs
The female lays her eggs singly on the leaves of the host plant, walking over the foliage and testing it with her feet before she commits. Each egg is small, round and whitish, no more than about half a millimetre across, and metalmark eggs of this type have a finely sculptured shell that looks pitted under a lens. They are placed on or near fresh growth and hatch within roughly a week in warm weather.
Caterpillar
The caterpillar is whitish green and unmistakably furry, clothed in long, fine pale hairs that stand out from the body in tufts. The body itself is short, broad and slightly flattened, with the head tucked underneath and out of sight, so a feeding larva looks more like a scrap of woolly plant fluff than an insect. It grazes on the leaves of its legume host, resting between meals on the underside of a leaf where the hairs break up its outline. Many metalmark caterpillars in the tropics have glands that feed ants in exchange for protection; whether the blue metalmark does this has not been established, and the hairs alone appear to deter small predators.
Chrysalis
The chrysalis is short, rounded and also covered with fine hairs. It is fastened with a silk pad and a girdle of silk around the middle, either on the host plant itself or, quite often, in leaf litter on the ground beneath it. The hairy, dull surface makes it look like a fragment of debris. In the warm months the adult emerges after roughly two weeks; late-season pupae carry the population through the short subtropical winter.
Adult butterfly
Adults are on the wing from April through December in south Texas, with a peak in the late summer and autumn when tropical rains bring the thorn forest into flower. Individual butterflies live only a week or two. Because the generations overlap, fresh, brilliantly blue males and faded, scale-worn ones can be seen on the same bush on the same afternoon, and the difference in colour is a matter of wear rather than of age class or subspecies.
Where the blue metalmark lives
The blue metalmark is a tropical butterfly that just reaches the United States. Its stronghold is Mexico and northern Central America, from where it ranges south to Honduras, and its northern limit is the Lower Rio Grande Valley of south Texas, in Cameron, Hidalgo and Starr counties. It is resident there rather than a stray, and in a good year it can be one of the commonest small butterflies in the remaining native brush. It does not stray far north of the Valley, so for most of the butterflies of Texas it is a species of the far south only, and the great majority of its world population lives among the butterflies of Mexico.
Its habitat is subtropical thorn woodland and the open, sunny ground around it: brushy fields, woodland edges, the banks of resacas and irrigation ditches, dirt roads through native scrub, and old citrus groves and gardens where enough native brush survives. The butterfly needs sunlit perches rather than deep shade, and it is usually found within a few feet of the ground. Because the Valley's native thorn forest has been very heavily cleared for farmland and building, this butterfly is now largely confined in the United States to protected tracts and to the strips of brush that remain along watercourses.
Host plants and diet
Caterpillar host plants. The larval host plants reported for the blue metalmark are legumes of the genus Albizia, small trees and shrubs of the pea family with feathery, twice-divided leaves. The larval biology of the species is poorly documented, and other thorn-forest legumes with the same leaf type, including acacias, have been suggested as additional hosts. What is clear is that the butterfly is tied to woody legumes of the native brush rather than to grasses or garden plants, which is one reason it disappears when thorn forest is cleared.
Adult diet. Adults drink flower nectar and are not fussy about the source, provided the flowers are small and the landing platform is flat. Favourites in the Valley include Spanish needles and other composites, crucita and mistflowers, croton, heliotrope and Texas lantana, all of which flower heavily after late-summer rain. Feeding butterflies keep the wings half open and turn slowly around the flower head. Males also settle on damp earth after rain to take up salts, though far less conspicuously than swallowtails and sulphurs do.
Behavior: perching, flight and daily routine
Flat basking. The defining habit of this butterfly is the way it holds its wings. It lands with them pressed completely flat and open against a leaf, a stone or the bare ground and angles its body to catch the sun. That posture warms the thorax quickly, which matters for an insect this small, and it also displays the male's metallic blue to any butterfly passing overhead. On cool mornings the flat basking is the only reason the species can be active at all before mid-morning.
Perching males. Males choose a sunlit leaf one to three feet above the ground and keep it for hours, flying out in a fast, buzzing dash at anything that passes, including other metalmarks, small flies and even falling leaves, and then returning to the same spot. This perch-and-intercept strategy replaces the long patrolling flights of larger butterflies, and a disturbed male usually returns to the same leaf within a minute.
Flight. The flight itself is low, quick and jerky, rarely more than a few feet at a time and rarely more than waist height. It is not a wandering butterfly, and marked individuals stay in a very small area for their whole adult life. Our guide to how butterflies mate and reproduce describes the courtship sequence that follows once a perching male intercepts a female rather than a rival.
Rest and shelter. Late in the afternoon, in cloud and at night, the butterflies move under leaves and sit with the wings closed, where the grey chequered underside makes them very hard to find. Strong wind empties the brush in the same way, and the butterflies reappear the moment the sun returns.
Similar butterflies and how to tell them apart
| Species | Looks like | How to separate it from the blue metalmark |
|---|---|---|
| Ceraunus blue and other small blues, Hemiargus and relatives | Small blue butterflies in the same fields | Rest with the wings closed over the back, showing a pale grey underside with round black spots and often an orange eyespot; the blue is soft lavender, not metallic, and the antennae are shorter |
| Fatal and rounded metalmarks, Calephelis species | Small metalmarks with the same flat basking posture | Rusty orange-brown, never blue, with two fine metallic silver lines running across each wing; commoner and more widespread in Texas than the blue metalmark |
| Red-bordered metalmark, Caria ino | Valley metalmark with metallic scaling | Grey-brown with a broad rusty red border and bands of glittering green-gold scales; larger-looking and much more strongly patterned |
| Female blue metalmark | Mistaken for a skipper or a small moth | Chequered grey-brown with black spots; identify it by the long white-ringed antennae, the flat basking posture and the company of blue males |
| Swamp metalmark, Calephelis muticum | Another North American metalmark | Bright orange-brown with metallic lines, restricted to wet meadows and fens far to the north and east; the ranges do not overlap |
| Harlequin, Taxila haquinus | Metalmark of similar size and habits | An Asian species, brown and white with bold dark blotches; it shares only the family, the four-legged males and the habit of perching under leaves |
Quick facts
| Scientific name | Lasaia sula |
|---|---|
| Family | Riodinidae (metalmarks), subfamily Riodininae |
| Wingspan | 0.9–1.3 in (22–32 mm) |
| Distribution | Lower Rio Grande Valley of south Texas, south through Mexico to Honduras |
| Habitat | Subtropical thorn woodland, brushy fields, woodland edges, canal banks and dirt roads through native scrub |
| Host plants | Legumes, reported as Albizia species and possibly related thorn-forest trees |
| Adult food | Nectar of small flowers such as Spanish needles, mistflower, croton, heliotrope and lantana |
| Flight season | April to December in Texas, peaking after late-summer rain |
| Broods | Several overlapping generations a year |
| Lifespan of adults | Roughly one to two weeks |
| Sexual dimorphism | Strong: males metallic blue-green above, females chequered grey-brown |
| Conservation status | Not listed; secure across its tropical range but limited in the United States by the loss of native thorn forest |
Did you know?
- It is the only blue metalmark in the United States. Every other member of the family north of Mexico is orange, brown or grey, so a small blue butterfly sitting with its wings flat open in the Rio Grande Valley has only one name.
- The blue is made of light, not paint. Ridged scales split and recombine the light that hits them, so the colour changes with the angle and disappears entirely when the scales wear off. Our guide to butterfly colours explains how structural colour differs from pigment.
- Male metalmarks walk on four legs. The forelegs are shortened into useless brushes, a reduction that happened independently in this family and in the brush-footed butterflies. Females keep all six, which they need for drumming on a leaf to identify a host plant.
- Metalmarks are overwhelmingly a tropical American family. Well over a thousand species are known from Central and South America, and only about two dozen reach the United States.
- The name comes from the metallic spots and streaks on the wings of many species. In the blue metalmark that metallic quality has spread across the male's whole wing instead of being confined to a few marks.
- Its flight season, April into December, is one of the longest of any butterfly in Texas, because there is no real winter to shut breeding down. Most adults still live only a week or two, as our guide to how long butterflies live explains.
In summary
The blue metalmark is a small, flat-basking butterfly of subtropical thorn woodland from south Texas to Honduras. Males are metallic blue-green with black chequering, females plain grey-brown, and both share a greyish chequered underside. Eggs go singly on legume foliage, the caterpillar and the chrysalis are covered in fine pale hairs, and overlapping broods fly from April to December. Watch for a small butterfly that lands with its wings pressed completely open on a sunlit leaf and comes straight back to the same perch.
Blue Metalmark butterfly pictures
Frequently asked questions about the blue metalmark butterfly
What is a blue metalmark butterfly?
The blue metalmark, Lasaia sula, is a small member of the metalmark family Riodinidae. The male is metallic blue-green above with rows of black dots, the female is chequered grey-brown, and both are about an inch across. It lives in subtropical thorn woodland from the Lower Rio Grande Valley of Texas south to Honduras and is the only blue metalmark in the United States.
How can you tell male and female blue metalmarks apart?
Only when the wings are open. The male shows shimmering blue-green across all four wings, broken by small black dots and dashes and bordered with grey. The female has no blue at all: her upperside is a chequered pattern of grey and grey-brown with the same black spots. With the wings closed the sexes look identical, because both undersides are greyish brown and chequered.
What do blue metalmark caterpillars eat?
They eat the leaves of woody legumes. The host plants reported for this species belong to the genus Albizia, small trees and shrubs of the pea family with feathery divided foliage, and other thorn-forest legumes may be used as well. The larval stages are poorly documented, but the butterfly is clearly tied to native brush rather than to garden plants or grasses.
Where are blue metalmark butterflies found?
They are resident in the Lower Rio Grande Valley of south Texas, mainly in Cameron, Hidalgo and Starr counties, and range south through eastern Mexico to Honduras. They live in subtropical thorn woodland, brushy fields, woodland edges, canal banks and tracks through native scrub, usually within a few feet of the ground and always where there are sunlit perches.
When is the flight season of the blue metalmark?
In south Texas adults fly from April through December, one of the longest seasons of any butterfly in the state. Several broods overlap, so all stages can be present at once, and numbers usually peak in late summer and autumn when tropical rains bring the thorn forest into flower. Individual adults live only about one to two weeks.
What does the blue metalmark chrysalis look like?
It is short and rounded and, like the caterpillar, covered in fine pale hairs, which makes it look like a scrap of plant debris. It is held in place by a silk pad and a silk girdle around the middle, either on the host plant or among leaf litter on the ground beneath it. In warm weather the adult emerges after roughly two weeks.
What colour are blue metalmark caterpillars?
Whitish green, with a short, broad, slightly flattened body clothed in long pale hairs that stand out in tufts. The head is tucked underneath and cannot be seen from above, so a feeding larva resembles a piece of woolly plant fluff on the leaf. It rests on the underside of leaves between meals, where the hairs break up its outline.
Why do blue metalmarks sit with their wings flat open?
Flat basking warms the flight muscles fast, which matters a great deal for a butterfly this small, and it also displays the male's metallic blue to rivals and to passing females. It is the quickest way to tell a metalmark from a small blue of the family Lycaenidae, which almost always rests with its wings folded up over its back.
Is the blue metalmark butterfly rare?
It is common and secure through Mexico and Central America, but in the United States it is confined to the far south of Texas and depends on the native thorn forest that has been very heavily cleared for farming and building. It is not federally listed, yet in the Valley it is now mostly seen on protected tracts and in the brush left along watercourses.
How do you tell a blue metalmark from a small blue butterfly?
Watch how it lands. A blue metalmark presses its wings completely flat against the surface; a blue of the family Lycaenidae folds them upright over its back and shows a pale, round-spotted underside. The metalmark's blue is metallic and greenish with black chequering, and its antennae are long and ringed with white.
