Butterflies belong to the same insect order, Lepidoptera, as moths, but they are generally not attracted to artificial light sources with the same intensity as their nocturnal relatives. The common sight of moths erratically circling a porch light often leads to the question of whether butterflies exhibit this behavior. The answer is predominantly no, stemming from fundamental biological differences between the two groups. Butterflies exhibit this response only occasionally and under very specific circumstances.
The Fundamental Distinction: Diurnal Behavior
The primary reason for the difference in light attraction lies in the activity patterns of the two insect groups. Butterflies are predominantly diurnal organisms, meaning their active period for feeding, mating, and flying occurs during the daytime. Their biology is adapted to the presence of bright, full-spectrum sunlight. Butterfly species rely heavily on visual cues, such as flower color and shape, to locate nectar sources, and complex color patterns for courtship. Moths, in sharp contrast, are mostly nocturnal, having evolved to operate in low-light conditions. They typically navigate and find food or mates under the illumination of the moon and stars. Since butterflies rest at night, artificial lighting is irrelevant to their behavioral needs and does not interfere with their natural, sun-based navigation system.
Understanding Insect Orientation and Light
The phenomenon of insects flying toward light is known as positive phototaxis, a directed movement response to a light stimulus. This behavior is closely linked to an insect’s natural method of navigation, often called transverse orientation or compass orientation. To fly in a straight line, nocturnal insects like moths keep a distant celestial light source, such as the moon, at a constant angle relative to their flight path. Because the moon is so far away, maintaining this fixed angle allows the insect to travel a straight course. When a moth encounters a much closer, brighter artificial light, it instinctively attempts to maintain the same constant angle. As the moth flies, the angle between its body and the nearby light source changes rapidly. The insect tries to correct for this change by turning inward, resulting in the characteristic, disoriented spiral flight path that draws it closer to the light. Another recently proposed model suggests that nocturnal insects tilt their dorsum toward the brightest light source to maintain flight attitude, which also leads to circling an artificial light.
Observed Butterfly Responses to Artificial Illumination
Butterflies do not exhibit the same sustained attraction as moths, but they are occasionally observed near artificial lights. These instances are typically sporadic and not representative of the chaotic, light-trapping behavior seen in most moths. One explanation for incidental attraction involves the need for heat; some butterflies may be drawn to the warmth emitted by older incandescent bulbs during cool evenings to raise their body temperature for flight. Furthermore, butterfly species that undertake long-distance migrations, such as the Painted Lady, may fly near dusk or dawn. If a migrating butterfly flies into the night, it may become accidentally disoriented by artificial light, exhibiting a brief, confused attraction. Scientific records indicate that some butterfly species, including the Nymphalidae and Pieridae families, show an occasional response to light sources. This attraction is sometimes linked to the presence of ultraviolet (UV) wavelengths in the artificial light, a part of the spectrum that butterflies are highly sensitive to for visual tasks like foraging and mating.