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Strymon melinus

By Lauren Rodriguez

Geographic Range

Gray hairstreaks can be found in Southern Canada to Central America and Northwestern South America. They occur from coast to coast and in a variety of altitudes ranging from sea level to nine thousand feet. (Carter, 1992; Tveten and Tveten, 1996)

Habitat

Unlike most butterflies, gray hairstreaks do not prefer one specific habitat. They are widespread in tropical forests and open, temperate woodland areas. They can also be found in meadows, crop fields, neglected roadsides, and residential parks and yards are often homes of this fascinating butterfly. (Carter, 1992; Milne and Milne, 1980; Scott, 1986; Tveten and Tveten, 1996)

  • Range elevation
    0 to 2745 m
    0.00 to 9005.91 ft

Physical Description

In the earlier stages of the life cycle, gray hairstreaks are straw, purplish-white, pink, reddish-brown, or green larvae with various other paler marks. The head is yellowish-brown. Throuhout Texas, however, the larvae have been noted to be entirely green and covered with short hairs. The pupae hibernate and are usually brownish in color. In the adult stages of the life cycle the butterfly's upper wings are dark grayish brown with a prominent orange spot located at the outer margin close to the shorter of the two blackish tails. The conspicuous orange spot is larger than most Strymon species. The hind wing is gray (darker in males and spring adults than in females and summer adults). It too has a black-eyed orange spot at the bases of the hindwing tails. There is a small patch of blue before the tail, and two broken crossbands of black and white spots. The male abdomen is orange. The wingspan varies from 2.6 to 3.65 cm. (Carter, 1992; Milne and Milne, 1980; Scott, 1986; Tveten and Tveten, 1996)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Range wingspan
    2.6 to 3.65 cm
    1.02 to 1.44 in

Development

After about six days the eggs hatch, and over the next twenty days the caterpillars grow and develop. They then form a chrysalis and after about ten days emerge as adults. Silvery-blues spend the winter as pupae and can have three or more generations per year. Development time can vary greatly depending on geography and the different hosts. (Drees and Jackman, 1998; Scott, 1986; Tveten and Tveten, 1996)

Reproduction

Mating and egg-laying occur in early spring. Adult males perch on small trees and shrubs from early afternoon to dusk to await females. They usually perch at a level where they can catch cooler breezes, lower to the ground in the spring and higher as the year goes on. Males back dorsally. Mating pairs are normally spotted at night, and females oviposit during the midafternoon. The females then lay their pale green eggs on hosts' buds or newly opened flowers of the host plant. (Drees and Jackman, 1998; Scott, 1986; Tveten and Tveten, 1996)

  • Breeding season
    early spring

There is no parental involvement once eggs are laid.

  • Parental Investment
  • pre-fertilization
    • provisioning

Behavior

The adults are quick fliers and are seen most often between the months of May and September. They like to bask in the sun with wings spread wide, unlike most hairstreaks, but they also rub their hindwings together in the typical fashion of most hairstreaks. This back-and-forth movement makes the wings look like anntennae, apparently to fool predators into attacking a less vital part of their body. They are best seen when at rest and their wings are folded together over the back, one hind wing sometimes raised while the other is lowered. (Drees and Jackman, 1998; Milne and Milne, 1980; Tveten and Tveten, 1996)

Food Habits

Just as in many other characteristics of gray hairstreaks, their food habits are general. Neither the caterpillar nor the butterfly are specific to any certain plant or flower, but rather feed on a variety of plants. The larvae eat from at least twenty different families of plants, including the pea and mallow families. Normally they can be found eating fruits and flowers. They can also be found on maize, cotton and a variety of shrubs and trees. The butterfly feeds on nectar from a wide variety of flowers. (Carter, 1992; Milne and Milne, 1980; Scott, 1986; Tveten and Tveten, 1996)

  • Plant Foods
  • leaves
  • fruit
  • nectar
  • flowers

Ecosystem Roles

These generalists feed on (and likely pollinate) a wide variety of plants. They also may be eaten by a wide variety of predators.

  • Ecosystem Impact
  • pollinates

Economic Importance for Humans: Positive

Gray hairstreaks benefit humans just as so many other butterflies, bees, and small birds do. The butterfly participates in a mutualistic relationship with many flowering plants by receiving nutrients (nectar) and acting as a pollinator. (Milne and Milne, 1980; Tveten and Tveten, 1996)

Economic Importance for Humans: Negative

The larvae of gray hairstreaks, when abundant, can become pests to commercial crops, including cotton, beans, corn, and hops. Habits such as these have earned the caterpillar the common name of "cotton square borer" and "bean lycaenid". (Milne and Milne, 1980; Tveten and Tveten, 1996)

  • Negative Impacts
  • crop pest

Conservation Status

Gray hairstreaks are not currently endangered or threatened.

Other Comments

This butterfly is so abundant across the United States that some suggest that besides the monarch it should be named the national butterfly. (Tveten and Tveten, 1996)

Contributors

Matthew Wund (editor), University of Michigan-Ann Arbor.

Lauren Rodriguez (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

diapause

a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nectarivore

an animal that mainly eats nectar from flowers

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

Carter, D. 1992. Butterflies and Moths. New York: Dorling Kindersley.

Drees, B., J. Jackman. 1998. A Field Guide to Common Texas Insects. Houston: Gulf Publishing Company.

Milne, L., M. Milne. 1980. The Audubon Society Field Guide to North American Insects and Spiders. New York: Alfred A. Knopf, Inc..

Scott, J. 1986. The Butterflies of North America: A Natural History and Field Guide. California: Stanford University Press.

Tveten, J., G. Tveten. 1996. Butterflies of Houston and Southeast Texas. Austin: University of Texas Press.

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