Not all the small critters crawling about on little legs in suburban gardens are insects. Some are crustaceans. Like insects, crustaceans have a hard skeleton on the outside of their bodies and jointed legs. Crustaceans, however, have more than three pairs of legs (insects have three pairs), two pairs of antennae or feelers (insects have only one pair), and never have wings.
In fact, the crustaceans in the garden are more closely related to prawns, lobsters and crabs than they are to insects. Their closest relatives live in the sea, which is where the vast majority of the thousands of species of crustaceans live.
If you live in the damper eastern outskirts of Melbourne you may be lucky enough to have small yabbies burrowing in your lawn (see Information Sheet: Who’s digging in my lawn?). These are more familiar crustaceans than their smaller relatives and neighbours.
Three kinds of small crustaceans are common in suburban gardens in southern Australian cities.
Woodlice are oval, flat, dull-grey, segmented animals growing up to 17 mm long. The head has a pair of compound eyes and each of the first seven body segments supports a pair of short legs. Segments closer to the tail don’t have legs, but have shorter limbs underneath that act as ‘lungs’.
Woodlice dry out and die unless they remain sheltered from the direct sunlight. They spend most of their life hiding under logs, stones or pots, where they feed on rotting vegetation.
‘Woodlice’ is a plural word – the singular ‘woodlouse’ is rarely used. They are also called slaters – because they are the colour of slate.
Garden Slater, Porcellio scaber
Photographer: Alan Henderson / Source: Museum Victoria
They belong to the large group of crustaceans called Isopoda. The most common species in Australian gardens is the Garden Slater, Porcellio scaber, a name which means ‘rough little pig’ in Latin.
Pillbugs are oval, deep-bodied, shiny-grey and segmented. They grow to 18 mm long. Pillbugs are isopods like woodlice, so they have a similar arrangement of segments and legs. Unlike woodlice, they are able to roll into a tight ball when alarmed. Pillbugs also spend most of their time hiding in the grass, but occasionally are seen wandering in the sun.
Pillbug, Armadillidium vulgare
Photographer: Alan Henderson / Source Museum Victoria
The scientific name of the pillbug found in suburban gardens is Armadillidium vulgare, alluding to its similarity to an armadillo. Australians also call them ‘butcher-boys’.
Land hoppers are segmented, shiny, grey-brown crustaceans that are taller than they are wide. The seven pairs of legs are obvious, especially the longer ones near the back on which they can walk in a clumsy manner.
Land hopper, Arcitalitrus sylvaticus
Photographer: David Staples / Source: Museum Victoria
Land hoppers are usually seen when they hop, apparently in a hysterical manner, when they are disturbed from their preferred home in damp leaf-litter or under pot-plants in the garden. The common species can grow up to 9 mm long. Sometimes large numbers of land hoppers find their way indoors, where they quickly dry out to shrimp-coloured crisps.
Land hoppers belong to one of the most abundant groups of Crustacea, the Amphipoda. The common species in gardens in Melbourne and Sydney is called Arcitalitrus sylvaticus.
Native or foreign crustaceans?
The common woodlice and pillbugs in suburban gardens are not native Australian species. Both have been introduced to this country from Europe with the many garden plants brought here, probably starting in the 19th century. The two examples mentioned are among at least nine European species now in Australia.
The northern hemisphere species of isopods now dominate in gardens full of hundreds of other exotic species. Roses, camellias, hydrangeas and cabbages have all been imported to Australia. Just as these foreigners have replaced native plants in cities, so have exotic isopods replaced some of the 300 species of native terrestrial Australian isopods. Luckily most of these survive elsewhere, in forest and grassland litter, in just the sorts of places that woodlice and pillbugs usually inhabit.
Curiously, the reverse has happened with the Australian land hopper. Arcitalitrus sylvaticus is a native Australian species that is successful in most gardens. The same species has been imported to California and the UK, probably with Australian native plants taken overseas to beautify northern gardens.