Grayling (butterfly)

Hipparchia semele can be considered a specialist feeding species.[7] They tend to feed on the following plants:

Hipparchia semele sometimes lay their eggs on the green leaves that the larvae later feed on. Because the adult butterflies lay their eggs on the ground, the larvae can easily find the host plants to feed on. Therefore, laying eggs directly on host plants does not seem to be crucial for survival to adulthood.[8]

Note that information on this species applies to Great Britain and some details may not be consistent with the species in other parts of its range.

There is one generation per year. The eggs are laid from July to September singly, often on the food plant. H. semele eggs are white at first, but turn pale yellow as they develop. The egg stage generally lasts between two and three weeks.[1]

When the eggs hatch, the caterpillar grows slowly, feeding at night and typically hibernating during cold temperatures in a deep patch of grass.[1] The larvae are small and cream colored, and there are four moults.[1] The first-instar and second-instar larvae feed in mid-to-late summer and then hibernate, while still small, in the third instar, at the base of a tussock. Feeding then resumes in the spring and the last instar larvae are nocturnal, hiding in the base of grass tussocks during the day. These larval instars take place from August to June. By June, the larvae should be fully grown, and at this point the caterpillar spends most of its time basking in the sun on the bare ground or rocks.[2] The larvae are attracted to muddy puddles and sap from tree trunks.[1] When the time comes to pupate, the caterpillar spins a cocoon in the ground.

Pupation happens in a cavity lined with silk below the surface of the ground.[1] The pupa is unattached in an earth cell. The pupal stage lasts around four weeks. The pupa is formed from June to August and the adult butterflies emerge in August.

• 
  Egg
• 
  Larva
• 
  H. s. semele female
  Učka Nature Park, Croatia
• 
  H. s. atlantica
  Argyll, Scotland

• 
  Male
• 
  Male underside
• 
  Female
• 
  Female underside

Grayling butterfly engages in cryptic coloring behavior to camouflage into environment.

Hipparchia semele engages in cryptic coloring, or camouflage that makes it difficult to see them when they are resting on the bare ground, tree trunks, rocks, etc.[2] Their tan and brown colored wings help them conceal themselves. Usually at rest and when not in flight, the butterflies keep their wings closed, with their forewings tucked behind their hindwings. This helps them conceal their eyespots and makes them appear smaller, further helping them camouflage to their environment.

Additionally, the forewing of a Hipparchia semele has one large and one small eyespot. When the grayling butterfly believes it may have been detected by a predator, it exposes these spots. However, there may be a balance between their cryptic coloring behavior and the exposure of their conspicuous eye spots. Exposing their spots may increase detectability by their predators. Therefore, at rest, the grayling adopts its cryptic coloring position, pulling its forewings down behind its hindwings in order to conceal the eyespots.[4]

When it comes time to mate, male and female H. semele meet above a solitary tree in a wide and open area. This takes on many forms, from a tall tree in a heathland to bare patches of ground in sand dunes. The female lays her eggs on various fine-leaved grasses, including fescues, bents, and bromes, a few centimeters above the ground.[1]

Male butterflies exhibit behaviors for defending territories. Females choose males based on the best territory for them to lay their eggs in. These territorial males engage in competitions of flight performances where the winning male settles in the territory. Thermoregulation helps these butterflies prepare for maximum flight efficiency in order to gain ownership of the most optimal territory.[5]

Male graylings make short and frequent flights, both spontaneous and non-spontaneous. These may function as a signal of display for females.[5]

The male graylings’ courtship procedure for copulation may also serve to indicate to the female the amount and the nature of the males’ sex pheromones. Further research must be conducted to determine this for certain, but the courtship procedure likely plays a role in pheromone production. Hipparchia semele only copulate once, so determining the best possible male, based on the pheromones and courting procedure, is very important for reproductive success. Pheromone releasers are located all over the wings of the males.[9]

Grayling females partake in resource defense polygyny.[5] Females choose a territorial male in order to gain the best oviposition site.[5] This allows for a higher survival rate of the eggs, as well as the inheritance of the ability to defend the best territories which are attractive to females, leading to a higher reproductive rate of the offspring, thus allowing the female grayling a higher opportunity to propagate her genes.

Grayling male (right) courting female (left)

A complex courtship procedure is performed by grayling males for copulation. The male moves behind the female, and engages in short movements around her until they are facing each other. Then, the male raises his forewings slowly, and quickly lowers and closes them, continuing this rhythmically. He then spreads his antennae to create a circular shape, and spreads his wings so the forewings are separated from the hindwings. After closing the wings again slowly, the male moves around the female again, and attempts copulation.[9]

The grayling is a large and distinctive butterfly when in flight. The flight of a grayling is characterized by strong loops.[2]

The flying patterns of a grayling are also important in male-male interactions of territoriality. Initially, when defending a territory, each male grayling flies in a spiral motion, trying to be higher than and behind the other male. When this formation is stabilized, the two male graylings go into an alternating sequence of dives and climbs. At the end, the male that is able to achieve the highest position settles in the territory.[5]

The graylings prefer to live in open habitats, with easy access to the sun. This may be due to their ability to regulate their body temperature using the sun. When the temperature gets too cold, the grayling leans to expose its side towards the sunlight, therefore allowing its wings to gain heat from the sun. When the temperature gets too warm, the grayling stands straight, on its tiptoes, exposing its head towards the sun and keeping the majority of its body away.[2]

The male tends to orient its body and wings to control which parts of the body are exposed to the sun. This allows the grayling to keep its body temperature as close to the preferred level as possible. Therefore, at lower temperatures, the male grayling exposes as much of its body area as it can to increase the surface area facing the sun. This process is sometimes called sun-basking. This can raise body temperatures by up to 3 degrees Celsius. Contrarily, at high temperatures, the male grayling exposes as little of its body area as possible to the sun. This process can lower body temperatures by up to 2.5 degrees Celsius. At intermediate temperatures, the male grayling is often observed gradually changing his body orientation and posture in order to evenly spread the heat all over his body. This behavior can often be observed by male butterflies defending their territories.[5] Many times, the territories that male graylings defend are specific mating sites. Thermoregulation allows the male butterflies to maximize their efficiency, in order to prepare for optimal flight performance if another male enters the territory.[5]

Much of the Hipparchia semele’s common habitats, such as heathlands, have started to become transformed into agricultural land. The dry habitats are occupied by trees and other greenery, reducing the optimal available habitats for the graylings.[11]