If you watch carefully, you may notice lovely little hairstreak butterflies in your summer garden. A member of Lycaenidae, the second largest family of butterflies with over 6,000 species worldwide, the gray hairstreak (Strymon melinus) can be found from southern Canada to northern South America. Although they’re considered common, they are rarely seen in large numbers. Since they’re small—with a wingspan of up to only about an inch and a quarter—and flighty, they can be easily overlooked.
Male and female gray hairstreaks appear somewhat similar, although females have rounder and wider forewings, and a male’s abdomen during summer is pale orange toward the tip. Their dorsal wings are a bluish-gray, with an orange spot that resembles an eye—if you’re wondering why, read on. Their underside is ashy gray, with jagged bands of black lined with white, and two orange spots with black areas. There is seasonal variation in color.
“False head” pattern
When most hairstreak butterfly species land, they often perch with their head downward and their two sets of tails pointed upward (Winkler 1977). They have what’s known as a “false head” at their rear end (as far from their real head as possible), complete with tiny hindwing tails that masquerade as fake antennae. When they move their hind wings up and down in a sawing motion (Sourakov 2017), they attract attention to the rear wing — instead of their real head and body — which serves to deflect predator attacks. Those big “eyes” and moving “antennae” either scare away small would-be attackers, or trick other predators into attacking the wrong end of the butterfly so that the expendable part of the wings may be torn away and allow the butterfly to escape without mortal wounds.
It’s easy to assume that this defense would help hairstreaks survive attacks by birds and possibly larger invertebrates, and a 2013 study by Dr. Andrei Sourakov at the University of Florida demonstrated that the false head on the wings of the red-banded hairstreak allowed it to escape attack by a species of jumping spider, a predator with great eyesight (and an adorable face, close-up).
Large menu
Since gray hairstreaks are very widespread, they do not have a strong preference for host and nectar plants like many other lepidoptera species do, and they even do well in disturbed habitat like urban areas as long as it offers food, shelter, and sunlight. Adults feed on nectar from a variety of plants (often with short, tubular, composite flowers), including native goldenrod, wild onion, milkweed, dogbane, mint, etc. The male pictured below has found a patch of native yarrow (Achillea millefolium var. occidentals). Caterpillars’ menu reportedly includes hundreds of hosts in dozens of plant families, especially legumes, roses, and mallows, but also oaks, pines and strawberry plants. Young caterpillars eat flowers and fruits, while the older ones (at the final instar) may consume leaves. They pupate in a sheltered location like a curled leaf, and overwinter as pupae (James and Nunnallee 2011), possibly in wood piles, beneath loose bark, or in hollow trees or logs.
Relationship with ants
Speaking of good things to eat, many hairstreaks, including the gray, have a special mutualistic relationship with ants (known as myrmecophily), who use the caterpillars as a host of sorts, from which they harvest a nutritious liquid full of sugars and amino acids via the caterpillars’ dorsal nectary organ. In exchange for the yummy meals, the ants guard the caterpillars from predators throughout their larval life, and, needless to say, don’t eat the caterpillars themselves. So the next time you’re annoyed by ants, remember that they may be attending and protecting little caterpillars!
