Orange sulfur is another common name for the alfalfa butterfly (Colias eurytheme). The larvae of this butterfly feed, usually at night, on alfalfa and other legumes including peas, clover and lupines. Alfalfa butterfly larvae are often so numerous that they become a pest in alfalfa fields throughout their range – from Canada to Mexico. Since we live in an area where alfalfa is a major crop (Modoc County CA), Leonard and I tend to use the name alfalfa butterfly.
Male and female alfalfa butterflies differ in color and pattern. Males are yellow or orange with a dark marginal border around the dorsal forewings and hindwings. Female alfalfa butterflies are yellow, orange or occasionally white with incomplete dark borders on their dorsal wings. Alfalfa butterflies hybridize with clouded or common sulfur butterflies adding more variety to their appearance.
Alfalfa butterfly larvae, which hatch from red eggs laid singly on the host plants, are green with white and pink lines on each side. There may also be some black markings on the larvae. The larvae overwinter. In warmer climates the larvae overwinter without difficulty, however, at higher elevations and colder areas the survival rate of overwintering larvae is decreased.
Male alfalfa butterflies deposit spermatophores (a packet containing sperm and nutrients) in the female. Over time the spermatophore degenerates as sperm are extracted and the female uses the nutrients. Once the eggs are laid the female has a brief period of “rest” then begins to search for another mate. Female alfalfa butterflies can remate every four to six days up to four times in a season.
Female alfalfa butterflies are attracted to the reflected UV light on the males’ hindwings. Males choose females on the basis of the UV absorbing colors in their hindwings.
Alfalfa butterflies flit around in constant motion and usually have their wings folded when sitting. This alfalfa butterfly was lying on our driveway, already dead – a perfect specimen that I could not pass up.