Variable checkerspot

Appearance

The variable checkerspot is usually brown-black with extensive yellow, red and white spots on the dorsal wing. Their underside is usually contains yellow and orange bands. However, as its name suggests, the butterfly is highly variable in appearance. Dorsal color can range from a brick red background with brown and yellow markings in Sierra populations to yellow and black in northern Californian populations. Adult wingspan is 3.2 cm–5.7 cm .

Distribution

The variable checkerspot is found across western North America, ranging from Alaska in the north to Baja California and Mexico in the south. Its habitat is bounded to the west by the Pacific Ocean and it extends east past the Rocky Mountains into Montana, Wyoming, Colorado and New Mexico.

The butterfly's habitat encompasses a large variety of environments, including sagebrush flats, desert hills, prairies, open forests and alpine tundra.

Behavior

The variable checkerspot lays its eggs in clusters. Pre-diapause larvae often move to fresher parts of the plant in which they are laid to secure a better food source. Before they enter diapause, the larvae leave the food plant to seek better dormancy sites such as under the bark of dead branches, in the hollow stems of dried weeds and in rock crevices.

During diapause, some larvae are able to wake up and feed before re-entering dormancy. The larvae emerge from diapause between late January and mid-March. However, in high elevations, larvae can hibernate for several years. Pupation begins in early to middle April and the adult flight season begins between mid-April and May and continues into June. The adult variable checkerspot has a life span of around 15 days.During the flight season, large groups of variable checkerspot butterflies can be found across western North America. Individual butterflies are capable of recognizing suitable areas rich in larval food plants and do not usually linger in other parts of the landscape. This leads to populations of butterflies that are small, isolated and clearly separated from other populations. Females do not fly as much as males, who frequently fly around their habitats and perch in open areas while searching for female mates.

Flight times for the variable checkerspot vary regionally. Usually, the flight season lasts from April to June in California and Oregon, while it normally takes place from June to July further north and in higher elevations.

Habitat

The variable checkerspot is found across western North America, ranging from Alaska in the north to Baja California and Mexico in the south. Its habitat is bounded to the west by the Pacific Ocean and it extends east past the Rocky Mountains into Montana, Wyoming, Colorado and New Mexico.

The butterfly's habitat encompasses a large variety of environments, including sagebrush flats, desert hills, prairies, open forests and alpine tundra.

Reproduction

The principal food source for variable checkerspot larvae are the leaves of the flowering subshrub ''D. aurantiacus'' that also usually serve as its host plant. ''D. aurantiacus'' contains large amounts of a leaf phenolic resin, which helps resist water loss during drought. Laboratory and field studies have shown that increased resin content is negatively correlated to the growth and survivorship of variable checkerspot larvae, indicating that the phenolic resin in ''D. aurantiacus'' plays in important role in deterring larvae from feeding on leaves.

Another factor in ''D. aurantiacus'' plants that impacts larval growth is leaf nitrogen content. Unlike resin levels, heightened nitrogen levels are correlated with increased larval growth and survivorship. In a controlled experiment, larva that were fed a diet of fertilized ''D. aurantiacus'' plants, which contained 50% more nitrogen than unfertilized plants, experienced higher survival rates and growth than larvae that fed on unfertilized plants. While leaves with increased nitrogen content are the most attractive for the larvae, they are also the most valuable carbon-gainers for the plant. This leads to the activity patterns of larvae and ''D. aurantiacus'' plants synchronizing. Larvae emerge from diapause as ''D. aurantiacus'' plants start flowering. This is when the plants need the most carbon. The plants then concentrate their resin in their youngest leaves, which contain the largest amount of nitrogen; this resin deterrent forces larvae to feed on less valuable older leaves whose nitrogen content is lower. To maximize their own nutritional benefits, larvae selectively eat leaves with the highest available nitrogen:resin ratio. In addition, larvae exhibit a strong preference for feeding on host plant leaves that have been in the sun compared to leaves that have been in the shade.

Another less common host plant for variable checkerspot larvae is ''Scrophularia californica'', which lacks the resin defense system found in ''D. aurantiacus'' and is thus easier for larvae to digest. Larvae that feed on ''S. californica'' grow faster and larger than those that feed on ''D. aurantiacus''. While ''D. aurantiacus'' may not be the most nutritious food for the larvae, it is the most reliable and widespread host available to the variable checkerspot and is often the plant closest to nectar sources, leading to its role as principal host plant and food source for the larvae.

Food

The diet of the variable checkerspot changes dramatically with development: the larva has an herbivorous diet consisting entirely of plants while the adult butterfly feeds exclusively on nectar.The principal food source for variable checkerspot larvae are the leaves of the flowering subshrub ''D. aurantiacus'' that also usually serve as its host plant. ''D. aurantiacus'' contains large amounts of a leaf phenolic resin, which helps resist water loss during drought. Laboratory and field studies have shown that increased resin content is negatively correlated to the growth and survivorship of variable checkerspot larvae, indicating that the phenolic resin in ''D. aurantiacus'' plays in important role in deterring larvae from feeding on leaves.

Another factor in ''D. aurantiacus'' plants that impacts larval growth is leaf nitrogen content. Unlike resin levels, heightened nitrogen levels are correlated with increased larval growth and survivorship. In a controlled experiment, larva that were fed a diet of fertilized ''D. aurantiacus'' plants, which contained 50% more nitrogen than unfertilized plants, experienced higher survival rates and growth than larvae that fed on unfertilized plants. While leaves with increased nitrogen content are the most attractive for the larvae, they are also the most valuable carbon-gainers for the plant. This leads to the activity patterns of larvae and ''D. aurantiacus'' plants synchronizing. Larvae emerge from diapause as ''D. aurantiacus'' plants start flowering. This is when the plants need the most carbon. The plants then concentrate their resin in their youngest leaves, which contain the largest amount of nitrogen; this resin deterrent forces larvae to feed on less valuable older leaves whose nitrogen content is lower. To maximize their own nutritional benefits, larvae selectively eat leaves with the highest available nitrogen:resin ratio. In addition, larvae exhibit a strong preference for feeding on host plant leaves that have been in the sun compared to leaves that have been in the shade.

Another less common host plant for variable checkerspot larvae is ''Scrophularia californica'', which lacks the resin defense system found in ''D. aurantiacus'' and is thus easier for larvae to digest. Larvae that feed on ''S. californica'' grow faster and larger than those that feed on ''D. aurantiacus''. While ''D. aurantiacus'' may not be the most nutritious food for the larvae, it is the most reliable and widespread host available to the variable checkerspot and is often the plant closest to nectar sources, leading to its role as principal host plant and food source for the larvae.In contrast to the herbivorous diet of the larva, the adult variable checkerspot's main food source is the nectar it obtains from flowers. In Jasper Ridge Biological Park in California, an extremely well studied site, the nectar source most frequently used by adult butterflies is ''Eriodictyon californicum''.The diet of the adult butterfly has a large impact on the choice of ''D. aurantiacus'' as the oviposition site and larval host of the variable checkerspot. Adult butterflies prefer to oviposit on host sites that are close to nectar sources. In the Jasper Ridge site, ''D. aurantiacus'' is the host plant closest to the ''E. californicum'' nectar source. This proximity advantage overcomes its nutritional deficiencies compared to other host plants and leads to it being the principle host plant of variable checkerspot butterflies.

Defense

The variable checkerspot’s main predators are birds. Populations of the variable checkerspot, like most lepidopterans, are usually scarcely distributed and thus direct observation of avian predation on butterflies is rare.

One study analyzed the evidence of avian predation on the butterflies by the presence of a large number of detached variable checkerspot wings at a butterfly population center. These detached wings exhibited beak marks and characteristic triangular tears indicating that birds attacked the butterflies and detached their wings before eating the body. In addition to the remains of this successful predation, photographs of variable checkerspot butterflies show some individuals that exhibit beak marks and tears, indicating unsuccessful avian predation attempts.

Analysis of the avian predation on the variable checkerspot population has found that predators disproportionately attack female butterflies. This is because attacks are concentrated on butterflies that contain less intense red coloration. The male butterfly exhibits more variation in its coloration than the female, and can be more intensely red colored. This means that on average, females face more attacks than males do. Red serves as a warning color in many species of butterfly, so it is possible that diminished avian predation is linked to this warning signal. Indeed, the pressure exerted on the variable checkerspot by visually hunting avian predators may play an important role in the evolution of its wing coloration and pattern.The variable checkerspot, like many other butterflies, has developed a defense strategy of unpalatability to birds as a means of resisting predation. In a controlled experiment, would-be avian predators often exhibit head-shaking and beak-wiping behavior after killing a variable checkerspot, characteristic of tasting unpalatable prey. The unpleasant taste of the butterfly is likely due to the presence of irisoid glycoside compounds in the scrophulariaceous plants that make up the majority of its larval diet.