The small blue butterfly (Cupido minimus) is a tiny, beautiful butterfly found across much of the United States. With a wingspan of just 0.75-1.3 inches, it is one of the smallest butterflies in North America. The male upperwings are a striking, iridescent blue color, while the female is grayish-brown with some blue scales. The small blue gets its name from this brilliant blue coloration on the males.
The small blue is widely distributed but localized across much of the eastern United States, parts of the Midwest, and some western states. It lives in open habitats with low vegetation and requires plants in the pea family for caterpillar host plants. The small blue has one brood a year and overwinters as a caterpillar. It faces threats from habitat loss and fragmentation. Conservation efforts focus on preserving open, native grassland habitats with host plants.
Description and Identification
As its name indicates, the small blue is a tiny butterfly, making it easy to identify by size alone. With a wingspan of just 0.75-1.3 inches (19-32 mm), it is one of the smallest butterflies in the United States and Canada.
The brilliant blue coloration on the males’ upperwings gives the small blue its common name. The upperwings and tops of the males are an iridescent violet-blue, ranging from grayish blue to brilliant blue. The females are not blue, but rather grayish brown with a some faint blue scales, especially at the base of the wings. The undersides of the wings on both sexes are gray with small black spots and marginal orange marks along the edges. The bodies of both sexes are also gray above with some blue on the males.
In size, color, and shape, the small blue looks very similar to the eastern tailed blue and the western tailed blue. The main difference is the lack of tail-like projections on the hindwings that give the tailed blues their name. The small blue has rounded hindwings.
Distribution and Habitat
The small blue has a wide but localized distribution across much of the eastern United States, parts of the Midwest, and some western states. It is found from Maine, Ontario, and Minnesota south to Florida and eastern Texas and west to Colorado, Utah, and California.
This species inhabits open grassland areas with low vegetation, such as meadows, prairies, fields, pastures, and grassy power line cuts. It prefers areas with sandy or gravelly soil. The small blue generally does not thrive in areas with dense or overgrown vegetation. Its small size makes it difficult to navigate thick vegetation.
Some specific habitats inhabited by the small blue include pine barrens, oak savannas, coastal grasslands, mountain meadows, prairie remnants, limestone glades, and agricultural areas. It avoids wetlands and densely forested regions. Range maps show it scattered in localized colonies throughout its distribution.
Life Cycle
The small blue butterfly has a single generation each year and overwinters as a caterpillar. The flight period for the adults is highly variable based on location, lasting anywhere from May to September across its range. Peak flight times are usually June and July.
Males perch on low vegetation and watch for females. After mating, the female lays eggs singly on plants in the pea family, including milkvetches, vetch, clovers, and lupines. The tiny yellow eggs hatch about a week later. The larvae are also yellow with a brownish head capsule.
The caterpillars feed on flowers, fruits, and seeds of the host plant. They pass through 4 instars over 14-30 days before forming a chrysalis attached to leaves or debris. The caterpillar stage lasts longer in the north. Before overwintering as partially grown larvae, the caterpillars must reach at least the 2nd instar stage.
In spring, the caterpillars break diapause and resume feeding and growing. They reach full size in their 4th instar. The chrysalis stage lasts 7-14 days before the adult butterflies emerge. The small blue likely produces just one generation per year across its entire range. Far southern populations may have a partial second brood.
Diet
The small blue butterfly relies exclusively on plants in the pea family (Fabaceae) for its caterpillar host plants. This includes native species such as milkvetches (Astragalus spp.), vetch (Vicia spp.), lupines (Lupinus spp.), prairie clover (Dalea spp.), and nonnative clovers (Trifolium spp.).
Different populations may use different host plants depending on availability. For example, populations in the Appalachians use bush clover, while those in New England use crown vetch. The caterpillars feed on flowers, fruits, and seeds of the host plant.
As adults, the small blues drink nectar from a variety of flowering plants. Favored nectar sources include dogbane, selfheal, clover, fleabane, New Jersey tea, mountain mint, milkweed, and thistles. The adults do not visit flowers as often as some other butterfly species.
Behavior
The small blue butterfly exhibits patrolling behavior where the males fly low over the vegetation, watching for newly emerged females. The males are quite territorial, chasing away other males that enter their area. If a predator approaches, they may continue their patrols, even landing briefly on the predator. The small blues fly slowly and remain close to the ground.
Threats and Conservation
The small blue butterfly is not considered globally threatened and has no legal protective status. But it faces some significant threats, especially from habitat loss and degradation. As natural grassland habitat has declined across its range, so have many populations of the small blue. Other threats include:
– Habitat loss and fragmentation from development, agriculture, and fire suppression
– Invasive plant species that displace native host plants
– Pesticide use in agricultural areas
– Succession and vegetation overgrowth in undisturbed areas
– Climate change altering habitat suitability
Conservation recommendations for the small blue focus on protecting sufficient open, native grassland habitat with host plants. This includes preserving and restoring prairies, barrens, meadows, and inland dunes. Removing invasive species and mimicking natural disturbance like grazing or fire can help maintain optimal habitat. Using conservation grazing practices can allow for cattle grazing while also benefiting small blue populations. Surveying and monitoring populations is also important for conservation.
Significance to Humans
The small blue butterfly has little significant, direct impact on humans. As a relatively common butterfly with no crop or garden pest status, it is not economically or agriculturally important. And its tiny size makes it unlikely to be noticed by most people.
For butterfly enthusiasts, however, sighting a small blue may be a thrilling experience. Its diminutive size, flash of bright blue, and interesting habits make it appealing to watch. The small blue’s dependence on threatened grassland ecosystems also makes it an important indicator of the health of these fragile habitats. Protecting populations of the small blue helps conserve many other grassland species.
This attractive little butterfly brings a bit of delicate beauty to open landscapes across the United States. While often overlooked, the small blue is a valuable part of natural diversity. Learning to recognize and appreciate even small species like this is an important part of connecting with the living world.
Summary
| Scientific Name | Cupido minimus |
|---|---|
| Common Name | Small Blue |
| Wingspan | 0.75-1.3 inches (19-32 mm) |
| Identification | Tiny size, males bright blue above, females brown, rounded wings |
| Range | Throughout eastern US, Midwest, and some western states |
| Habitat | Open grasslands with low vegetation |
| Life Cycle | One generation per year, caterpillar overwinters |
| Host Plants | Pea family including milkvetches, vetch, clovers, lupines |
| Threats | Habitat loss, invasive species, pesticides, succession |
In summary, the small blue is the smallest blue butterfly in the United States at just 0.75-1.3 inches across. The flashing blue color of the males makes it distinctive, though females are brown. It lives in grasslands across much of the eastern and central US. The small blue relies on pea family host plants and produces one generation per year. Preserving its threatened grassland habitat is crucial for the conservation of this tiny butterfly.
