Porcellio scaber Latreille
Family: PorcellionidaeOrder: Isopoda
Pill bug and Roley Poley (usually refer to Armadillidium species that roll into a ball or pill when disturbed)
Summary:A grey, oval and flattish invertebrate with 7 pairs of legs and long antennae that hide under things in damp places and scurry off without rolling into a ball when disturbed. They are one of the few crustacea that live on dry land.
Description:Ectothermic or “cold blooded”.
Adult - Up to 20 mm long
Colour - grey and paler underneath. Brown, yellow or orange shades are occasionally seen.
Body - 7-20 mm long. Warty, flat, elliptical, heavily plated, segmented and bilaterally symmetrical. 7 body segments, each with a pair of legs.
Wings - None.
Antennae - 2 pairs and often orange coloured at the base. The inner pair is hard to see and are thought to act as chemoreceptors and a longer outer pair have sensory hair-like structures (setae).
Legs - 7 pairs
Head - 3 lobed.
Thorax - 7 body segments, each with a pair of legs.
Abdomen - There are two short tails (uropodia) on their final body segments (telsons).
They are sexually dimorphic, with females (and juveniles) mottled and lighter in colour.
Females have a brood pouch in which they carry developing young, while males have a genital projection located near their pleopodia.
For Slaters, the head, pereion and pleon terms are often used instead of head, thorax and abdomen.
Habits - Do not roll into a ball when threatened.
Eggs - Are carried in the female and emerge as adult-like mancae.
Mancae - Mancae are soft, white, and have only six pairs of legs. Two mancae stages occur within the pouch and two occur outside.
Does not roll into a ball when it is disturbed and tends to run for shelter.
"Crown" shaped head with rounded outer lobes.
Two pairs of projections on the uropods with the inner pair being much smaller.
The posterior end of the plates of the exoskeleton tend to come to a sharp point rather than being rounded.
Two pairs of pleopod lungs
The outer margin of the plates of the exoskeleton are slightly reverse curved in the upward direction.
Biology:Unlike insects, the pore on the “lungs” cannot be closed and they don't have a waxy cuticle which makes them more susceptible to desiccation than insects.
Slaters reproduce sexually, during warmer spring and summer seasons. Males insert sperm using their copulatory organ, a modification of their abdominal legs. This species is polyandrous; females mate with many males and broods have been shown to have greater than 80% multiple paternity.
It is possible for slaters to have one to three broods per year, with 12-36 offspring per brood. Females may survive long enough to breed in multiple seasons, but often do not. Reproduction typically occurs when the days lengthen and temperatures rise during spring and summer, and females have been noted to be gravid for an average of 35 days. Males and females can be distinguished by their sixth moult, and reach full sexual maturity within 14-22 months after hatching.
Males exhibit no parental investment after mating. Females carry eggs and mancae (developing young) in a fluid-filled breeding pouch in order to prevent their desiccation. Once mancae have been released there is no further parental involvement.
Although there is little information regarding lifespan for slaters, terrestrial isopods live between 1-5 years on average. It has been suggested that this species typically lives 2-3 years, though up to 90% die within a month of emerging from their brooding pouches.
Much of this species behaviour is related to its need for an appropriately humid environment; they will relocate based on whether they currently need more or less water in their systems. For example, in forest ecosystems, they have been observed in the upper parts of deciduous trees during summer months and in mossy areas around the bases of trees during autumn months. These woodlice are most active at night and their activity levels are correlated with wind speed; increased wind speeds (and, so, evaporation rates) lead to lower levels of activity. They exhibit negative phototaxis, moving away from lighter (likely warmer and drier) conditions to darker ones, and they speed up their movements when environmental conditions are outside of an optimal range. Humidity and temperature also affect whether or not these animals burrow into leaf litter. This species exhibits thigmokinesis, which means that their movement is reduced when in contact with other objects. This includes other slaters; aggregations can help to protect individuals from desiccation and predation.
These slaters have long antennae with setae, which sense movement, and shorter antennae which may function as chemoreceptors. They also sense their environments through touch, as evidenced by their thigmokinetic behaviour, which causes reduced movement when in physical contact with other objects. Slaters may use pheromones, either released by faeces or produced separately, to find others of their species in order to create aggregations. They have two compound eyes that can sense light and dark.
Slaters are detritivorous, saprophagous (including carrion), mycophagous, and coprophagous. They prefer decaying organic matter because of the higher population of microbes within this material. Slaters consume their own faeces in order to increase copper stores (necessary as their blood contains haemocyanin) and to retain bacteria that are able to break down nutrients that are not easily absorbed otherwise. These bacteria are a significant part of their diets. Slaters also have endosymbiotic bacteria (Candidatus Rhabdochlamydia porcellionis) living in the hepatopancreas, which help with cellulose digestion.
Slaters protect themselves from predation by hiding under wood, rocks, leaves and other detritus. Their bodies are also heavily plated. They also excrete nitrogenous waste in the form of ammonia gas instead of urine, which may help to ward off would-be predators. Nevertheless, slaters have a number of natural predators such as spiders (including Dysdera crocata, known as woodlouse hunters, which feed exclusively on them), small mammals (such as shrews), birds, centipedes, harvestmen, and ground beetles.
Slaters are detritivores that help with the degradation of organic matter, such as decaying leaves and wood. In its native regions, this works to quickly return nutrients to the soil. In some areas with a slower degradation process, introduced slaters significantly affect indigenous flora and fauna.
Melanophora roralis are parasitic flies that lay eggs on slaters, killing their hosts during their pupation. Other parasites include spiny headed worms and nematodes. Slaters also host intracellular parasitic bacteria in their guts.
Slaters are susceptible to Iridovirus (IIV) Type 31, which creates crystalline structures in the host's tissues, lending them a blue colour, and leading to death in extreme infections. This species may also become infected by Wolbachia, a bacteria that affects hormone production in males.
Slaters also have endosymbiotic bacteria that help them to digest plant matter living in their hepatopancreas.
Life Cycle:Slaters undergo direct development with 15-20 recognized stages, beginning with fertilization. These stages occur through a series of moults and are differentiated by morphological changes or development of organs. Eggs are carried in the female's fluid-filled brood pouch where they hatch; after hatching, they are referred to as mancae. There are two manca stages that take place within the pouch and two that occur outside of the pouch. Mancae are soft, white, and have only six pairs of legs; the seventh pair develops after their first moult. The development of the seventh pair of legs occurs outside of the pouch and, after this, the mancae are considered juveniles. Juveniles are similar in appearance to adult slaters.
Slaters usually eat decaying plant matter, but feed on root vegetables, windfall fruit and seedlings if soil moisture is low.
They can build up to large numbers
Slaters require moderate to high levels of relative humidity.
They are found in damp places, compost heaps, under bark, rocks and fallen logs, in garden debris and leaf litter or in splash zones, dunes and salt marshes.
Origin and History:Introduced from Europe.
Distribution:Temperate regions across the world.
Slaters are decomposers of wood and other organic matter, releasing minerals, nutrients and other chemicals into their environments. They are also useful as model organisms in many scientific studies and have been used to test contamination levels of heavy metals such as cadmium, lead and zinc in soil. (Godet, et al., 2011; Kaufman and Eaton, 2007; Kostanjsek, et al 2004)
Detrimental:May damage seedlings.
In some regions where it has been introduced, this species has had a negative impact on the niches of the native flora and fauna. These animals eat decaying matter, releasing nutrients into the soil, but this may not be ideal in regions that have developed without detritivores present. In regions that have, they may compete with native detritivore species.
Management and Control:Large numbers may cause damage to seedlings.
Dry out damp places to reduce the habitat available.
Reduce the amount of rotting organic matter and rotting wood around the premises.
Sprinkle iron chelate based snail pellets close to where slaters congregate or near plants requiring protection.
A number of insecticides will provide control.
Birds and hens will help keep the numbers down.
Thresholds:Control when damage is first seen.
Armadillidium vulgare is another imported slater that rolls up into a ball when disturbed.
Porcellio laevis is another imported slater
Sub species include:
Porcellio scaber americanus Arcangeli, 1932
Porcellio scaber flavobrunneus Collinge, 1917
Porcellio scaber flavomaculata Collinge, 1918
Porcellio scaber japonicus Verhoeff, 1928
Porcellio scaber lusitanus Verhoeff, 1907
Porcellio scaber scaber Latreille, 1804
References:Avidov, Z. and Harpaz, I. (1969) Plant Pest of Israel. Israel University Press. P
CSIRO. The Insects of Australia. Melbourne University Press. (1991)
Evans (1943) Insect Pests and their control. Department of Agriculture Tasmania.
Riggio, C. 2013. "Porcellio scaber" (On-line), Animal Diversity Web. Accessed April 13, 2014 at http://animaldiversity.ummz.umich.edu/accounts/Porcellio_scaber/
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