Biston strataria
Encyclopedia
The Oak Beauty is a moth of the family Geometridae. It is native to Europe
, but is primarily found in the United Kingdom
. B strataria is found in a variety of habitats, but is mostly found in woodlands where it rests on the bark of trees, camouflaged by its mottled black and gray wings. The male has feather-like antennae
while those of the female are more thread-like. The moth has a wingspan of 40 to 56 mm.
The larvae are mainly brown with three lumps near the end of the abdomen. They have evolved to resemble sticks which helps protect them from predators. The larvae feed on many species of trees, but the most commonly used host plants are oak
s.
The Oak Beauty exhibits melanism
and comes in two different variations; a dark (melanic) form and light (typica) form. The melanic form is prevalent in Holland, but this form has not been observed in Britain. Details explaining this discrepancy are not yet known. The closest relative to B. strataria is the Peppered moth (B. betularia), which also has two forms. The proportion of melanics is higher in B. betularia compared to B. strataria. This is unusual since, between the two species, it is B. strataria that should have a greater evolutionary selection for the prevalence of melanic individuals due to the higher pollution concentrations in the area.
and are frequently observed during the daytime. Such feathered antennae are thought to aid in sensing female pheromone
s from over a kilometer away. This helps males locate females for mating.
Females are observed less often during the day than their male counterparts, and their antennae are thinner and more threadlike than the males’.
In July and August, the larvae can be found feeding on various host plants. B. strataria is prevalent in wooded areas including parks, gardens, and other suburban habitats. It is usually found on the trunk of trees rather than within the canopies where it can blend with its surroundings
is brown, marbled with white, and has two small red lumps on the back of its eighth, ninth and twelfth segments and a small lump on the belly on the seventh, eighth and ninth segments. The caterpillar’s head is slightly notched in the middle, possibly due to evolutionary pressures to resemble twigs in appearance.
The larvae are found from spring to fall feed on a variety of deciduous trees including oak (Quercus spp.), elm
(Ulmus spp.), Hazel
(Corylus avellana), Aspen
(Populus tremula) and Alder (Alnus glutinosa).
, and Lycia hirtaria
were protected from jay
s and Chaffinch
es by their resemblance to the sticks they resided upon. In this experiment, the larvae and twigs were scattered across an area while seven Garrulus glandarius
were positioned to prey on the larvae. When the larvae were not confused as twigs, it took G. glandarius ten seconds to find their prey. When more twigs were present than caterpillars, it took the birds between one and forty minutes to find the larvae. After finding the first caterpillar, G. glandarius quickly increased its rate of attack on both the larvae and the twigs. This experiment concluded that these caterpillars' adaptation to their environment does not give them the best possible protection.
Tinbergen added on to de Ruiter’s experiments and found that when caterpillars were more abundant than twigs, birds continued to hunt; when caterpillars seemed rare in comparison to twigs, birds stopped hunting all together. Brower concludes that a bird’s continuous quest for caterpillars after discovering larvae puts surrounding larvae in danger, despite how well these caterpillars blend in with their environment. Brower has speculated that bird behavior is density-dependent as well as dependent upon finding surrounding larvae of the similar phenotypic properties to the one it just consumed. Although past theories have speculated that either Batesian mimicry
or crypsis
were at play to explain these circumstances, further studies by Skelhorn have proven neither are correct. Rather, this phenomenon is quite different from the former two and is now commonly recognized as masquerade.
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, but is primarily found in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. B strataria is found in a variety of habitats, but is mostly found in woodlands where it rests on the bark of trees, camouflaged by its mottled black and gray wings. The male has feather-like antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
while those of the female are more thread-like. The moth has a wingspan of 40 to 56 mm.
The larvae are mainly brown with three lumps near the end of the abdomen. They have evolved to resemble sticks which helps protect them from predators. The larvae feed on many species of trees, but the most commonly used host plants are oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
s.
Morphology
The Oak Beauty has white forewings with two irregular broad brown bands along each wing. The first band is short, located near the base of the wing, and surrounded with a black border. The second band is located near the outer margin with a black border surrounding the inner edge. Between these two bands is a white space sprinkled with black dots as well as a crescent-shaped black mark near the middle. The overall appearance gives the Oak Beauty a mottled look. B. strataria‘s forewings are 17-27 mm in diameter while its wingspan ranges from 40-56 mm. The Oak Beauty’s hind wings are paler than its fore wings and have transverse black bands. The forehead and the front of the thorax are white while its sides are a white-grey blend. Its body is covered with many hairs. The back of the thorax and the body are a darker shade of brown.The Oak Beauty exhibits melanism
Melanism
Melanism is an undue development of dark-colored pigment in the skin or its appendages, and the opposite of albinism. It is also the medical term for black jaundice.The word is deduced from the , meaning black pigment....
and comes in two different variations; a dark (melanic) form and light (typica) form. The melanic form is prevalent in Holland, but this form has not been observed in Britain. Details explaining this discrepancy are not yet known. The closest relative to B. strataria is the Peppered moth (B. betularia), which also has two forms. The proportion of melanics is higher in B. betularia compared to B. strataria. This is unusual since, between the two species, it is B. strataria that should have a greater evolutionary selection for the prevalence of melanic individuals due to the higher pollution concentrations in the area.
Sex differentiation
Adult males possess feathered antennaeAntenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
and are frequently observed during the daytime. Such feathered antennae are thought to aid in sensing female pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s from over a kilometer away. This helps males locate females for mating.
Females are observed less often during the day than their male counterparts, and their antennae are thinner and more threadlike than the males’.
Distribution and habitat
Although the Oak Beauty’s distribution stretches from central and southern Europe to Asia Minor, the moth is primarily confined to England and Wales and is occasionally spotted in Scotland and Ireland. Within the UK, the Oak Beauty has been found in western counties including Crom and Garvary. A few discoveries have been made in Argory and Peatlands in the late 1990s. They have also been rediscovered at Rostrevor Before this time the moth had not been seen since the early part of the twentieth century and sightings still remain relatively rare.In July and August, the larvae can be found feeding on various host plants. B. strataria is prevalent in wooded areas including parks, gardens, and other suburban habitats. It is usually found on the trunk of trees rather than within the canopies where it can blend with its surroundings
Behavior
Adults emerge in early spring. B. strataria begins its flight period from mid-March to April, which is an early flight period compared to other moth species. B. strataria usually flies at night and is readily attracted to light. Its mottled appearance aids in its concealment from predators when it rests on tree trunks during the day Although the adult camouflages well with its surroundings, predators may occasionally spot the moth. In these circumstances the moth has one last defense mechanism – its hindwings, which were previously hidden in the resting position, carries shocking markings which may warn off predators when suddenly exposed.Larvae
The Oak Beauty caterpillarCaterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
is brown, marbled with white, and has two small red lumps on the back of its eighth, ninth and twelfth segments and a small lump on the belly on the seventh, eighth and ninth segments. The caterpillar’s head is slightly notched in the middle, possibly due to evolutionary pressures to resemble twigs in appearance.
The larvae are found from spring to fall feed on a variety of deciduous trees including oak (Quercus spp.), elm
Elm
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The dozens of species are found in temperate and tropical-montane regions of North America and Eurasia, ranging southward into Indonesia. Elms are components of many kinds of natural forests...
(Ulmus spp.), Hazel
Corylus avellana
Corylus avellana, the Common Hazel, is a species of hazel native to Europe and western Asia, from the British Isles south to Iberia, Greece, Turkey and Cyprus, north to central Scandinavia, and east to the central Ural Mountains, the Caucasus, and northwestern Iran. It is an important component of...
(Corylus avellana), Aspen
Populus tremula
Populus tremula, commonly called aspen, common aspen, Eurasian aspen, European aspen, trembling poplar, or quaking aspen, is a species of poplar native to cool temperate regions of Europe and Asia, from the British Isles east to Kamchatka, north to inside the Arctic Circle in Scandinavia and...
(Populus tremula) and Alder (Alnus glutinosa).
Larvae
An experiment was carried out to discover whether caterpillars of B. strataria, Ennomos alniariaEnnomos alniaria
The Canary-shouldered Thorn is a moth of the family Geometridae. The species can be found in Europe.The wingspan is 34–42 mm. The length of the forewings is 16–20 mm. The moths fly in one generation from July to October. They are attracted to light.The larvae feed on a number of...
, and Lycia hirtaria
Brindled Beauty
The Brindled Beauty is a small Palearctic moth.-Description:The Brindled Beauty is a furry moth, which has brown wings with a brindled brown and white pattern which provides near-perfect camouflage on tree trunks and also gives the moth its name. The females have a pale yellow suffusion on the...
were protected from jay
Jay
The jays are several species of medium-sized, usually colorful and noisy, passerine birds in the crow family Corvidae. The names jay and magpie are somewhat interchangeable, and the evolutionary relationships are rather complex...
s and Chaffinch
Chaffinch
The Chaffinch , also called by a wide variety of other names, is a small passerine bird in the finch family Fringillidae.- Description :...
es by their resemblance to the sticks they resided upon. In this experiment, the larvae and twigs were scattered across an area while seven Garrulus glandarius
Eurasian Jay
The Eurasian Jay is a species of bird occurring over a vast region from Western Europe and north-west Africa to the Indian Subcontinent and further to the eastern seaboard of Asia and down into south-east Asia...
were positioned to prey on the larvae. When the larvae were not confused as twigs, it took G. glandarius ten seconds to find their prey. When more twigs were present than caterpillars, it took the birds between one and forty minutes to find the larvae. After finding the first caterpillar, G. glandarius quickly increased its rate of attack on both the larvae and the twigs. This experiment concluded that these caterpillars' adaptation to their environment does not give them the best possible protection.
Tinbergen added on to de Ruiter’s experiments and found that when caterpillars were more abundant than twigs, birds continued to hunt; when caterpillars seemed rare in comparison to twigs, birds stopped hunting all together. Brower concludes that a bird’s continuous quest for caterpillars after discovering larvae puts surrounding larvae in danger, despite how well these caterpillars blend in with their environment. Brower has speculated that bird behavior is density-dependent as well as dependent upon finding surrounding larvae of the similar phenotypic properties to the one it just consumed. Although past theories have speculated that either Batesian mimicry
Batesian mimicry
Batesian mimicry is a form of mimicry typified by a situation where a harmless species has evolved to imitate the warning signals of a harmful species directed at a common predator...
or crypsis
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
were at play to explain these circumstances, further studies by Skelhorn have proven neither are correct. Rather, this phenomenon is quite different from the former two and is now commonly recognized as masquerade.