The natural decline of an introduced species following its initial increase in abundance; an explanation for Ommatoiulus moreletii in Australia

Summary The black Portuguese millipede, Ommatoiulus moreletii, an exotic species first reported in Australia in 1953, shows a pattern of initial eruption and subsequent decline in abundance following its introduction to sites in South Australia. Comparative sampling of new, erupted populations and older, declined populations was done in an attempt to find testable hypotheses to account for the decline. We report on laboratory and field experiments which show that a native rhabditid nematode appears to be the causal agent for the decline of populations of O. moreletii in South Australia. Implications for the biological control of introduced species are discussed in terms of this work.     

Summer quiescent behaviour of the millipede Ommatoiulus moreleti (Julida: Julidae)

The millipede Ommatoiulus moreleti (Lucas), (Julidae) originates in the south-west Iberian Peninsula, and has successfully invaded parts of southern Australia with hot, dry summers. The species is inactive in the field during summer but is active in autumn, particularly following rains, and in spring. There is some activity in winter. In this paper, the temperature and humidity determinants of seasonal behaviour are analysed, in particular the conditions causing summer quiescence.
Experiments using a millipede treadmill apparatus at different temperatures at 95% RH showed an almost linear response of locomotor activity with temperature between 3 and 21°C, but when the temperature was increased to 28°C, the millipedes became quiescent. Activity could he restored by reducing the temperature.
When the millipedes were exposed to 45% RH there was comparatively little activity at any temperature. Field evidence indicates ii rapid breaking of quiescence with surface moisture
The success of O. moreleti in invading the surface-litter habitat in South Australia can he explained by its ability to avoid desiccation; its adaptations include its quiescent behaviour during summer and its ability to moult from a winter (reproductive) to B summer (non-reproductive) form.     

Diversity, endemism and species turnover of millipedes within the south-western Australian global biodiversity hotspot

Aim To examine how current and historical environmental gradients affect patterns of millipede (Diplopoda) endemism and species turnover in a global hotspot of floristic diversity, and to identify regions of high endemism and taxonomic distinctness for conservation management. Location South‐western Australia. Methods Museum database records of millipedes (subclasses Pentazonia and Helminthomorpha), supplemented with extensive fieldwork, were used to map species richness, species turnover (β‐diversity), weighted endemism, average taxonomic distinctness and variation in taxonomic distinctness in half‐degree grid squares (c. 2500 km²). Generalized linear models were used to examine relationships between these parameters with rainfall (present day and historical), topography and human disturbance (clearing for agriculture and urbanization). Results Millipede species richness, particularly within the order Spirostreptida, and millipede endemism were positively associated with large within‐cell differences in elevation (mountainous regions). Large variation in taxonomic distinctness (unevenness in the taxonomic tree) in higher‐rainfall areas was mainly due to speciation within the Spirostreptida genus Atelomastix. Hotspots of millipede endemism and taxonomic distinctness were identified within three categories of importance: primary (Stirling Range East, Cape Le Grand, Cape Arid, Walpole, Porongurups), secondary (Mount Manypeaks, Bremer Bay, Stirling Range West, Duke of Orleans Bay, Ravensthorpe, Albany, Busselton) and tertiary (Nornalup). A species turnover boundary was positively associated with rainfall, broadly located in the transition zone of 300–600 mm year^?1. Main conclusions The current lack of knowledge on the endemism of invertebrates hampers their incorporation into conservation planning. With this knowledge we can identify global biodiversity hotspots and, at a smaller scale, significant conservation areas within a region. Here we have shown that weighted endemism and taxonomic distinctness are useful tools in identifying centres of high endemism and speciation for millipedes within the south‐west Australian hotspot. Moreover, it is unlikely that either vertebrates or vascular plants will be useful surrogates for identifying significant areas for invertebrate conservation. While other workers have shown that vascular plants, mammals and frogs have different centres of endemism within south‐west Australia, our results show that centres of endemism for millipedes encompass all of these plus other areas.     

The Impact of the Weed Chrysanthemoides monilifera ssp. rotundata on Coastal Leaf Litter Invertebrates

In coastal areas of Australia, there are extensive infestations of the environmental weed Chrysanthemoides monilifera ssp. rotundata (bitou bush). This study looked at the impact of long-term infestations on the abundance and assemblage composition of leaf litter invertebrates. Assemblages were compared in weed infested and native shrublands along the New South Wales coastline over 12 months. The total abundance was not significantly reduced in the weedy habitat but the abundance of mites, thrips, spiders, ants, and centipedes was reduced at many sites. The invertebrate assemblages also differed between habitats, with the C. monilifera supporting a lower diversity of beetles. However, the millipedes, amphipods, earthworms, pseudoscorpions and isopods appeared to respond positively to the invasion, occurring in higher abundance and detected more frequently in the weedy areas. This has been partially attributed to a change in microclimate within the C. monilifera infestations. It is generally moister and darker, which these invertebrates tend to prefer. Secondly, C. monilifera produces less leaf litter of higher quality, and possibly higher palatability than the native sclerophyllous vegetation, which may encourage species that consume litter.     

Guilty by association: an evaluation of millipedes as pests of carrot and sweet potato

An evaluation of the pest potential of millipede species occurring in Ontario sweet potato and carrot fields was conducted in response to recent grower concerns about the presence of millipedes in close proximity to damaged vegetables. This study is the first North American survey of millipedes on arable soils and the first evaluation of North American millipede damage to sweet potatoes and carrots. Through field surveys, Cylindroiulus caeruleocinctus was found to be the dominant millipede species in Ontario sweet potatoes and carrots. Fields were surveyed over the growing season, and the factors important to each species’ abundance were evaluated using Minimum AIC Estimation (MAICE). Post‐harvest damage assessments were performed, and MAICE analysis was used to determine which arthropod and environmental parameters were most important in explaining damage to sweet potatoes and carrots. Wireworm (Elateridae) abundance was consistently found to explain root damage better than C. caeruleocinctus abundance, and it is concluded that the majority of field‐observed damage was caused by wireworms. C. caeruleocinctus was negatively correlated with both wireworms and damage in carrot fields and is not likely to be a pest of that vegetable. However, abundance of C. caeruleocinctus in sweet potatoes was positively correlated with both wireworms and damage. This species may cause some damage to sweet potato tubers under field conditions, but management tactics should focus on wireworms as the primary source of damage.     

The distribution and dispersal of the introduced millipede, Ommatoiulus moreletii (Diplopoda: Iulidae), in Australia

The millipede, Ommatoiulus moreletii, is indigenous to South-Western Europe. The species has been introduced to Australia where it is in large numbers and constitutes a severe nuisance.
The distribution of O. moreletii in Australia is increasing. Man appears to be a major factor in the establishment of new outbreaks of the species. Individual outbreaks spread slowly but steadily (an expansion of up to 200 metres in radius per year).
The abundance of O. moreletii in Australia relative to its apparent rarity in Southwestern Europe cannot be explained by differences in general climate.
The variety of habitats colonized by O. moreletii in Australia is already wide and there is no reason to doubt that the species will continue to spread much further.     

Millipede consumption and interaction between food preferences and sex in dung beetle Chalconotus convexus (Coleoptera: Scarabaeinae)

Dung beetles feed mainly on scarce and ephemeral mammalian faeces making them vulnerable to declines of mammal populations. Therefore, studying how diverse groups like the Scarabaeinae subfamily utilize alternative food sources, such as decomposing invertebrates, enhances our understanding of their distribution and resilience in defaunated areas. One poorly studied aspect of the feeding habits of dung beetles is the potential differences between the sexes and their predatory behaviour. We evaluated how the sex (male and female) of individuals of Chalconotus convexus affected individual resource attraction to different bait types. Since C. convexus is known to feed on faeces, carrion and dead millipedes, we also test whether it can predate live individuals of millipedes. We used a combination of two field samplings and one laboratory experiment, using pitfall traps baited with faeces, carrion, millipedes and millipede's defensive compounds. While the preference for millipede was not associated with sex, we found a significant relationship between faeces and carrion, where females of C. convexus are significantly less attracted to faeces when compared to males and also males are significantly less attracted to carrion when compared to females. Furthermore, we also show that while actively consuming dead millipedes, C. convexus is unable to predate on live individuals. Our study illustrates that the versatility of food sources may help to explain the high abundance and wide distribution of C. convexus in Africa.     

Colonization of Colliery Spoil Heaps by Millipedes (Diplopoda) and Terrestrial Isopods (Oniscidea) in the Sokolov Region, Czech Republic

Successive development of millipede and terrestrial isopod assemblages in colliery spoil heaps in the Sokolov region (northwest Bohemia, Czech Republic) was studied during the years 1993–1998. Younger colliery spoil heaps were characterized by a lower number and low density of millipede species. The millipedes Polydesmus inconstans, Polydesmus testaceus, and Craspedosoma rawlinsii represented the main pioneer species. Alder afforestation proved to be more suitable for the recolonization of millipede populations, especially for the predominant Julus scandinavius. Terrestrial isopods colonized all parts of the heaps, including the youngest open plots. The most frequent isopod, Trachelipus rathkii, is a colonizing species with an apparently high adaptability to different environmental conditions. The isolated character of the extensive heap areas, together with existing extreme soil conditions, resulted in slow recolonization and a successional development of stable populations of these animals. However, the relatively high densities of millipede and isopod assemblages in suitable alder afforestation can represent further potential sources for colonization of other open‐heap areas.     

Distribution of millipedes (Myriapoda,Diplopoda) along a forest interior – forest edge – grassland habitat complex

We studied the distribution of millipedes in a forest interior-forest edge-grassland habitat complex in the Hajdúság Landscape Protection Area (NE Hungary). The habitat types were as follows: (1) lowland oak forest, (2) forest edge with increased ground vegetation and shrub cover, and (3) mesophilous grassland. We collected millipedes by litter and soil sifting. There were overall 30 sifted litter and soil samples: 3 habitat types × 2 replicates × 5 soil and litter samples per habitats. We collected 9 millipede species; the most abundant species was Glomeris tetrasticha, which was the most abundant species in the forest edge as well. The most abundant species in the forest interior was Kryphioiulus occultus, while the most abundant species in the grassland was Megaphyllum unilineatum. Our result showed that the number of millipede species was significantly lower in the grassland than in the forest or in the edge, however there were no significant difference in the number of species between the forest interior and the forest edge. We found significantly the highest number of millipede individuals in the forest edge. There were differences in the composition of the millipede assemblages of the three habitats. The results of the DCCA showed that forest edge and forest interior habitats were clearly separated from the grassland habitats. The forest edge habitat was characterized by high air temperature, high soil moisture, high soil pH, high soil enzyme activity, high shrub cover and low canopy cover. The IndVal and the DCCA methods revealed the following character species of the forest edge habitats: Glomeris tetrasticha and Leptoiulus cibdellus. Changes in millipede abundance and composition were highly correlated with the vegetation structure.     

Spatial variability of an invasive earthworm (<Emphasis Type="Italic">Amynthas agrestis</Emphasis>) population and potential impacts on soil characteristics and millipedes in the Great Smoky Mountains National Park,USA

European and Asian earthworm invasions are widespread in North America. European earthworms especially are well-known to cause dramatic changes in ecosystems in northern, formerly glaciated portions of the continent, but less is known about the impacts of earthworm invasions in unglaciated areas inhabited by indigenous earthworms. We monitored fluctuations in the spatial extent of an Amynthas agrestis (Megascolecidae) population in the Great Smoky Mountains National Park in eastern Tennessee, USA. Two years of monthly growing-season observations revealed that the distribution of the earthworm population was dynamic, but overall distribution was closely linked to temperature and moisture with dramatic reductions of earthworm numbers associated with very dry conditions. In plots where A. agrestis were more often detected, we measured increased A-horizon soil aggregation and decreased thickness of the Oe/Oa-horizon. However, A. agrestis was not related to A-horizon microbial biomass, A-horizon C:N, Oi-horizon (litter) thickness, or mass of forest floor (O-horizon). Reductions in millipede species richness and density were associated with frequency of A. agrestis presence, possibly due to direct competition for food resources (Oe/Oa material). This evidence for potentially negative interactions between millipedes and A. agrestis suggests that expansion of the non-native earthworm into new habitats in the Park may alter soil physical properties and could pose a threat to native millipede diversity.     

Seasonal changes in habitat preferences of two closely related millipede species

The habitat preferences of two closely related millipede species, Centrobolus richardii and C. fulgidus, were investigated on three different seral stages of a coastal dune forest successional sere north of Richards Bay, South Africa. Fixed‐width transects were used to survey millipedes in three habitats of different ages. Habitat preference occurred on both inter‐ and intra‐site levels and was influenced by season. A habitat shift was recorded for C. richardii, while C. fulgidus was dormant during the winter months, reflecting two different strategies used by these closely related species to meet their resource requirements. Successional changes previously reported are masked by these differential responses.     

PRESENCE OF CIRCADIAN RHYTHMS IN THE LOCOMOTOR ACTIVITY OF A CAVE-DWELLING MILLIPEDE GLYPHIULUS CAVERNICOLUS SULU (CAMBALIDAE,SPIROSTREPTIDA)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757–765, 2000)     

The impact of invasive cane toads on native wildlife in southern Australia

Commonly, invaders have different impacts in different places. The spread of cane toads (Rhinella marina: Bufonidae) has been devastating for native fauna in tropical Australia, but the toads' impact remains unstudied in temperate‐zone Australia. We surveyed habitat characteristics and fauna in campgrounds along the central eastern coast of Australia, in eight sites that have been colonized by cane toads and another eight that have not. The presence of cane toads was associated with lower faunal abundance and species richness, and a difference in species composition. Populations of three species of large lizards (land mullets Bellatorias major, eastern water dragons Intellagama lesueurii, and lace monitors Varanus varius) and a snake (red‐bellied blacksnake Pseudechis porphyriacus) were lower (by 84 to 100%) in areas with toads. The scarcity of scavenging lace monitors in toad‐invaded areas translated into a 52% decrease in rates of carrion removal (based on camera traps at bait stations) and an increase (by 61%) in numbers of brush turkeys (Alectura lathami). The invasion of cane toads through temperate‐zone Australia appears to have reduced populations of at least four anurophagous predators, facilitated other taxa, and decreased rates of scavenging. Our data identify a paradox: The impacts of cane toads are at least as devastating in southern Australia as in the tropics, yet we know far more about toad invasion in the sparsely populated wilderness areas of tropical Australia than in the densely populated southeastern seaboard.     

Cryptic species, native populations and biological invasions by a eucalypt forest pathogen

Human‐associated introduction of pathogens and consequent invasions is very evident in areas where no related organisms existed before. In areas where related but distinct populations or closely related cryptic species already exist, the invasion process is much harder to unravel. In this study, the population structure of the Eucalyptus leaf pathogen Teratosphaeria nubilosa was studied within its native range in Australia, including both commercial plantations and native forests. A collection of 521 isolates from across its distribution was characterized using eight microsatellite loci, resulting in 112 multilocus haplotypes (MLHs). Multivariate and Bayesian analyses of the population conducted in structure revealed three genetically isolated groups (A, B and C), with no evidence for recombination or hybridization among groups, even when they co‐occur in the same plantation. DNA sequence data of the ITS (n = 32), β‐tubulin (n = 32) and 27 anonymous loci (n = 16) were consistent with microsatellite data in suggesting that T. nubilosa should be considered as a species complex. Patterns of genetic diversity provided evidence of biological invasions by the pathogen within Australia in the states of Western Australia and New South Wales and helped unravel the pattern of invasion beyond Australia into New Zealand, Brazil and Uruguay. No significant genetic differences in pathogen populations collected in native forests and commercial plantations were observed. This emphasizes the importance of sanitation in the acquisition of nursery stock for the establishment of commercial plantations.     

The introduction and release of Chiasmia inconspicua and C. assimilis (Lepidoptera: Geometridae) for the biological control of Acacia nilotica in Australia

Two geometrid moths Chiasmia inconspicua and Chiasmia assimilis, identified as potential biological control agents for prickly acacia Acacia nilotica subsp. indica, were collected in Kenya and imported into quarantine facilities in Australia where laboratory cultures were established. Aspects of the biologies of both insects were studied and CLIMEX® models indicating the climatically favourable areas of Australia were developed. Host range tests were conducted using an approved test list of 74 plant species and no-choice tests of neonate larvae placed on both cut foliage and potted plants. C. inconspicua developed through to adult on prickly acacia and, in small numbers, Acacia pulchella. C. assimilis developed through to adult on prickly acacia and also in very small numbers on A. pulchella, A. deanei, A. decurrens, and A. mearnsii. In all experiments, the response on prickly acacia could be clearly differentiated from the responses on the non-target species. Both insects were approved for release in Australia. Over a three-year period releases were made at multiple sites in north Queensland, almost all in inland areas. There was no evidence of either insect’s establishment and both colonies were terminated. A new colony of C. assimilis was subsequently established from insects collected in South Africa and releases of C. assimilis from this new colony were made into coastal and inland infestations of prickly acacia. Establishment was rapid at one coastal site and the insect quickly spread to other infestations. Establishment at one inland area was also confirmed in early 2006. The establishment in coastal areas supported a CLIMEX model that indicated that the climate of coastal areas was more suitable than inland areas.     

Diversity and function of fungi associated with the fungivorous millipede,Brachycybe lecontii

Fungivorous millipedes (subterclass Colobognatha) likely represent some of the earliest known mycophagous terrestrial arthropods, yet their fungal associates remain elusive. Here we describe relationships between fungi and the fungivorous millipede, Brachycybe lecontii. Their fungal community is surprisingly diverse, including 176 genera, 39 orders, four phyla, and several undescribed species. Of particular interest are twelve genera conserved across wood substrates and millipede clades that comprise the core fungal community of B. lecontii. Wood decay fungi, long speculated to serve as the primary food source for Brachycybe species, were absent from this core assemblage and proved lethal to millipedes in pathogenicity assays while entomopathogenic Hypocreales were more common in the core but had little effect on millipede health. This study represents the first survey of fungal communities associated with any colobognath millipede, and these results offer a glimpse into the complexity of millipede fungal communities.     

Distribution of Elements in the Millipede, <Emphasis Type="BoldItalic">Oxidus gracilis</Emphasis> C. L. Koch (Polydesmida: Paradoxosomatidae) and the Relation to Environmental Habitats

The concentrations of 55 elements in the millipede, Oxidus gracilis, soil and plant in the habitat were examined using inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). In all the millipedes, Ca concentration derived from calcium carbonate in the exoskeleton was the highest at average 94 μ/mg-weight. The other major elements were the following: Mg, K, Na, Zn, Fe, Al, Cu, Sr, Ba, Mn and Ti (> 1 ng/mg-body weight), whereas Se, Mo, Ag, Cd, Co, Li and Ce etc. were in trace levels. Interestingly, the various 15 elements such as Ca, Na, Zn, Al, Ba, Ga, Ag, Cd, Co and Y in environmental habitats were well reflected in the body of the millipede. Although the heavy metal contents, in the order of Cu>Pb>Cd, were similar to those of other invertebrates, Cu in the millipede was remarkably high concentration. Zn was maintained in a range of 72–394 ng/mg-weight as essential element in the body and no difference was found in the sexes. The C1 chondrite normalization pattern for lanthanoid series elements in the millipede, soil and plant indicated that the environmental habitats were well protected from pollution. These characteristics of internal elements and metal accumulation in the millipede or relation to their habitats would be useful information for the environmental pollution studies.     

Failure to cospeciate: an unsorted tale of millipedes and mites

Mites form symbiotic relationships with many animal taxa, including fish, amphibians, reptiles, birds, mammals, mollusks and arthropods. They are often found living on millipedes and it has often been speculated that these two groups of arthropods have, in some cases, undergone coevolution. However, this hypothesis has never been formally tested. Millipedes of the family Xystodesmidae Cook 1895 (Diplopoda: Polydesmida) and their symbiotic mites of the genus Stylochyrus Canestrini & Canestrini 1882 were collected in broadleaf forests of the eastern USA. The DNA from two mitochondrial regions (16S/12S and cox1) was sequenced for all collected millipede and mite specimens. Phylogenetic trees were reconstructed for both millipede and mite taxa using Bayesian inference. Pairwise distance data were used in distance‐based coevolutionary analyses and reconstructed phylogenies were used in tree‐based coevolutionary analyses. The phylogenetic analyses indicate Stylochyrus and xystodesmid millipede evolutionary history is incongruent. Moreover, the evolutionary relationships among mite individuals and populations have very low support values and indicate little to no geographic structuring. The coevolutionary analyses likewise detected no pattern of coevolution among these millipede and mite lineages. Unlike many arthropod species, Stylochyrus mites appear to be highly vagile. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 272–287.     

Anamorphosis in millipedes (Diplopoda)—the present state of knowledge with some developmental and phylogenetic considerations

A review of the postembryonic development of millipedes (Diplopoda) is given, based mainly on published information. Original observations are, however, also included. Millipedes hatching from the pupoid usually have three pairs of legs; during their postembryonic growth they acquire more segments and more legs. This process is known as anamorphosis. Three types of anamorphosis are recognized. In euanamorphosis, every moult is accompanied by addition of new segments, even after the attainment of sexual maturity. In hemianamorphosis, the addition of new segments goes on until a certain stadium, and further moults take place without addition of segments. In teloanamorphosis, the addition of segments stops at a certain stadium (the adult, and ultimate, stadium) after which no further moults occur. Available information on anamorphosis in each of the millipede orders is reviewed. General patterns are emphasized, but variations are also considered in detail. It is shown that the so-called ‘law of anamorphosis’ is valid only for the ‘ring-forming’ millipedes (Merocheta and Juliformia) in which tergites, pleurites, and sternites of each diplosegment are firmly fused into a complete ‘ring’, and for some other forms (Polyzoniida, Chordeumatida), where there is a constant relationship between rings and legs. The chapter on the order Julida is particularly detailed and includes discussions of patterns in the variation and a section on periodomorphosis. The general chapter on developmental patterns includes inter alia an interpretation of the variations in millipede anamorphosis in terms of the ‘biometabolic modi’ of Remane. The hypothetical ancestral millipede is shown to have developed by hemianamorphosis. Euanamorphosis was acquired by the ancestral species of Helminthomorpha. Within this clade, Chordeumatida and Merocheta have secondarily become teloanamorphic, whereas some Juliformia seem to have returned to hemianamorphosis. The contrasting principles of elongation and contraction, subject of much debate among diplopodologists, are shown both to have played a role in the course of millipede evolution.     

Mechanical properties of calcified exoskeleton from the neotropical millipede, Nyssodesmus python

The calcified exoskeleton of millipedes plays a crucial role in resisting large forces developed during burrowing locomotion. I measured morphological and mechanical properties of cuticle from the neotropical forest floor millipede, Nyssodesmus python (Diplopoda: Polydesmidae), which ranges in body mass from 2 to 7 g. Scaling of thickness of the cuticle with respect to body mass followed predictions of geometric similarity. Both fracture strength and Young's modulus increased with body mass in females but not in males. In spite of their smaller size, male millipedes were still stronger, on average, than female millipedes. Mean fracture strength of millipede cuticle was 124 MPa, and Young's modulus was 17 GPa. Both of these values exceed measurements from typical insect cuticle, suggesting that calcium salts may play a role in stiffening and strengthening the millipede exoskeleton. Because of the high density of calcified millipede cuticle (1660 kg/m³), stiffness and strength relative to body weight remain comparable to values for other insect cuticles. These results corroborate a previous hypothesis that absolute not specific strength and stiffness have been selective factors in the evolution of millipede cuticle, and that bulkiness of the exoskeleton has been minimized through the deposition of calcium salts.