Q: What’s small and wriggly and prevents trains from running?
A: The Portuguese millipede (Ommatoiulus moreleti).
Since the 1970s, these invertebrates have been causing
transportation mayhem, initially on the Belair line to the Adelaide
Hills. In 2002, Ballarat line trains in Victoria were delayed or cancelled
some 50 times in one month when masses of squashed millipedes
made the tracks too slippery. It occurred again in 2009 at Tallarook,
Victoria, causing cancellations and delays, and in 2013, millipedes
were even implicated in a low-impact train crash in Perth, WA!
The species was first noticed near Port Lincoln, SA, in 1953,
when it invaded houses in plague proportions in autumn, and to a
lesser extent in spring. How O. moreleti gained entry into Australia
is anyone’s guess, but in the 1960s outbreaks were recorded in
the Adelaide Hills and Melbourne, and later in Launceston, Perth,
and Canberra. Essentially, the millipedes invade an area, peak after
around a decade, and then abate but never really go away. These
millipedes also invade agricultural and native habitats in high numbers.
Millipedes are best known for feeding on dead organic matter on
the soil surface and on the fungi that live on it. In 1985, I predicted
regions of Australia where this pest might extend its distribution
in time, based on the areas it had already reached. Two decades
later, I wondered whether my prediction was right. Thus, another
opportunity arose to enlist the help of Double Helix members.
In 2007, following on from the success of Earthworms Downunder,
approximately 450 participants were involved in ‘Millipede Mayhem’,
hunting for millipedes in their gardens. In particular, they collected
O. moreleti, if they could find them. They’re easy to recognise and so
prolific that you’ll know it if you’ve got them! O. moreleti is more or
less uniformly black in colour all over when fully grown, with paler
coloured legs. It coils into a tight, flat spiral when inactive, and has a
little spike at the very end of its tail.Once again, the children posted their collections to CSIRO
for verification. Most of the records for O. moreleti did indeed
fall within the predicted distribution. It will be interesting to see
whether this pest remains confined to that range. Most media
attention on O. moreleti has previously focused on its nuisance
value, but it has recently also become a significant pest of seedling
grain crops in South Australia. One can’t help but question what
the pest’s impact has been on the other invertebrate fauna it shares
the soil surface with in native woodlands. We do know that its
abundance can run to several hundred individuals per square metre
in peak periods. Such biomass must be influencing something in
these habitats and perhaps even interfering with processes driven by
native soil fauna. Perhaps that is a concept that a current or future
generation of enthusiastic citizen scientists might help us explore.READING Baker GH, et al. 1997. Earthworms Downunder: a survey of the
earthworm fauna of urban and agricultural soils in Australia. Soil Biology & Biochemistry
29:589–597. Baker G, Barrett V. 1994 Earthworm Identifier. CSIRO Australia,
Melbourne. Edwards CA (Ed). 2004. Earthworm Ecology. CRC Press, Boca Raton.
Hopkin SP, Read HJ. 1992. The Biology of Millipedes. Oxford University Press,
Oxford. Baker GH, Grevinga L, Banks N. 2013 Invasions of the Portuguese millipede,
Ommatoiulus moreleti, in southern Australia. Pedobiologia 56:213–218.DR GEOFF BAKER is a Post Retirement Fellow at CSIRO Health &
Biosecurity in Canberra. His research has included the ecology and
management – especially biological control – of exotic pests such as
Portuguese millipedes and Mediterranean snails, the role of earthworms in
enhancing soil structure and fertility, and the ecology of moth (Helicoverpa
spp.) pests, in particular their potential development of resistance to
transgenic (Bt) cotton.MILLIPEDE
Portuguese millipedes commonly invade homes
in outbreak areas. Photo: Rebecca Hamby.MAYHEM
THE OTHER 99%
PART-TIME EUNUCHSThe Portuguese millipede has an intriguing life history. As an individual grows, it
moults its external cuticle about nine times before reaching maturity. At that time,
the legs on the male millipede’s seventh segment change to become an elaborate
spiky set of gonopods used to transfer sperm to the female during mating season.
But the next time the male moults, he loses this complex structure, which is replaced
by rudimentary stubs, becoming a temporary eunuch. If lucky enough to survive and
moult again, he regains his mature gonopods, and so on. Having this eunuch stage
(known as an intercalary stage) in the life cycle is called ‘periodomorphosis’. The
benefits periodomorphosis provides to O. moreleti are poorly understood, but it certainly
quietens the males down out of season!
A male’s spiky gonopods vanish and reappear over the life cycle. Photo: Geoff Baker14 | Wildlife Australia | SPRING 2017