Phalangium opilio (also known as the Common harvestman, brown harvestman and daddy longlegs) is a species of harvestman belonging to the family Phalangiidae.
Taxonomy
P. opilio is a member of the Eupnoi suborder of Opiliones.
Distribution
P. opilio has a mostly holarctic distribution and is the most widespread harvestman species worldwide, occurring natively in Europe, North and Central Asia, and Asia Minor. The species has been introduced to North America, North Africa and New Zealand from Europe. In North America, it occurs in non-desert regions of southern Canada and the United States.
Habitat
This species can be found in a wide range of open habitats, including meadows, bogs, and forests. It is also most abundant in anthropogenic habitats, and is thus considered a synanthropic species of harvestmen. In can be found in habitats modified by humans, such as gardens, agroecosystems, hedgerows, lawns, quarries, urban green spaces, walls and bridges. In agricultural settings, P. opilio is common in temperate cropland, living among crops such as corn, alfalfa, small grains, potatoes, cabbage, strawberries, and apple.
P. opilio apparently prefer vertical surfaces, including tree trunks and vertical man-made structures like fences and walls, with a preference for wood substrate due to its low thermal conductivity and slow release of moisture, being a thermophilous and moderately hygrophilous species. However, their preference varies based on the amount of cover available in a certain area. P. opilio tend to be found in shrubs and brushy vegetation when sparse shrub cover exists, but tend to be found on the ground layer when dense cover is present, such as low vegetation and grass. Early instars, immature P. opilio, only occur on the ground, but later instars have a broader vertical range. P. opilio have also been observed to take cover in low vegetation, like grass, during rain.
Description
Like other harvestmen, P. opilio have long, slender legs and a short, round body. Adult P. opilio have a body length of . Males tend to have smaller bodies than females. Both sexes are similarly coloured and are marked light brown and gray, often with a light cream underside.
P. opilio is relatively large compared to other harvestmen species. Individuals of both sexes have very long pedipalps, and their legs, bodies, and eye tubercles are covered with spines. Males can be differentiated from females by their longer pedipalps and the existence of long, forward-pointing processes, appearing similar to horns, on the second segment of their chelicerae. In some European populations, P. opilio male chelicerae and pedipalpal size have significant allometric variation, but it's not clear whether this is continuous or discrete, which would indicate male dimorphism in P. opilio.
As an arachnid species, P. opilio have four pairs of legs. Three of these pairs are for movement, but the longest, second pair is antennae-shaped and used as a sensory appendage to feel their surroundings. Their tarsus, the segment of their legs furthest from their body, have numerous pseudosegments called tarsomeres that make them prehensile, enabling P. opilio to use them in climbing, such as by curling them around twigs; courtship of mates; and male—male combat. Their legs have seven segments, whereas pedipalps have six.
Juveniles
Immature P. opilio resemble adults, but have shorter legs relative to their bodies and are smaller overall.
Eggs
P. opilio'''s eggs are smooth, spherical in shape, and about 0.4 mm in diameter, laid in clusters ranging from ten to several hundred. As they mature, their color changes from off-white to dark grey-brown. Clutches consist of about 250 eggs in total with embryos that develop at the same time. Each egg has a thin, opaque chorion membrane and a thick, transparent vitelline membrane.
Similar speciesMitopus morio has a very similar appearance, but P. opilio can be distinguished by the two pale "denticles" (small teeth-like structures) below the anterior margin of the carapace, as well as the long forward-pointing "horns" on the second segment of male P. opilio's chelicerae.