field observations on three scolopendrid centipedes from

Biology of three scolopendrid centipedes 123

Field observations on three scolopendrid centipedes from Mauritius and Rodrigues (Indian Ocean)

(Chilopoda: Scolopendromorpha)

John G.E. Lewis1*, Peter Daszak2, Carl G. Jones3, Janet D. Cottingham4,

Esther Wenman5 & Aleksandra Maljkovic6

1 Somerset County Museum, Taunton Castle, Castle Green, Taunton, Somerset TA1 4AA and Entomology Department, Natural History Museum, Cromwell Road, London, SW7 5BD, UK.

Address for Correspondence: Manor Mill Farm, Halse, Taunton, Somerset TA4 3AQ, UK.2 School of Life Sciences, Kingston University, Penrhyn Road, Kingston-upon-Th ames, Surrey KT1

2EE, UK. Present address: Wildlife Trust, 460 west 34th Street, New York 10001, USA.3 Mauritian Wildlife Foundation, Black River, Mauritius and Durrell Wildlife Conservation Trust,

Les Augres Manor, Trinity, Jersey, Channel Island, UK.4 Wildlife Trust, 460 west 34th Street, New York 10001, USA.

5 Th e Zoological Society of London, Regent’s Park, London, NW1 4RY, UK.6 Mauritian Wildlife Foundation, Solitude, Rodrigues. Present address: Tropical Marine Ecology Lab.,

Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6.

* Corresponding author: [email protected]

Abstract

Biological observations on three species of Scolopendra (S. morsitans L., 1758; S. subspinipes Leach, 1815; S. abnormis Lewis & Daszak, 1996) were made in the fi eld on Mauritius and Rodrigues and satellite is-lands. Data on behaviour, predators, parasites, food and the eff ect of bites are presented here. Remarks on colour variation are given. Scolopendra abnormis is confi ned to Round Island and Serpent Island. It showed no ritualised meeting reactions and cannot swim as do some other species and did not run off when ex-posed. Th e diff erences between the populations of this species on the two islands are discussed, as are its conservation prospects (it is classifi ed as vulnerable). Th e large specimens of Scolopendra on Rodrigues will kill and feed on day old chicks and are attracted to strong smelling fi sh. A case of a centipede feeding on a baby is reported. Centipedes form the main diet of feral cats on the Rodrigues Île Frégate. Th e origin of the Scolopendra fauna of the islands is discussed and it is suggested that the introduction of the musk shrew [Suncus murinus (L., 1766)] may be responsible for the precipitous decline in the population of large centipedes on Rodrigues.

© Koninklijke Brill NV and Pensoft, 2010 DOI: 10.1163/187525410X12578602960425

International Journal of Myriapodology 3 (2010) 123-137 Sofi a–Moscow

Downloaded from Brill.com05/30/2022 02:55:53PMvia free access

John G.E. Lewis et al. / International Journal of Myriapodology 3 (2010) 123-137124

Key words

Chilopoda, Scolopendromorpha, Scolopendra, Mauritius, Rodrigues, Biology

Introduction

Six scolopendrid species are found on Mauritius and Rodrigues (Lewis 2002), three belonging to the genus Scolopendra L., 1758, namely: Scolopendra morsitans L., 1758, S. abnormis Lewis and Daszak, 1996, and S. subspinipes subspinipes Leach, 1815. Mauritius is located at 20ºS and 57ºE in the Indian Ocean. Rodrigues is 574 km east of Mauritius.

Field observations were made on Round Island (151 hectares) and Serpent Island (40 hectares), two remnants of a volcanic cone some 21 km off the North-eastern shore of Mauritius. On Rodrigues observations were made at Solitude and Port Maturin Hill and also on Île aux Sables and Île Cocos (two small coral sand islets) and Île Frégate (14 hectares) off the west coast of Rodrigues (Fig. 1). Scolopendra abnormis is confi ned to Round and Serpent Islands.

Figure 1. Mauritius and Rodrigues showing localities where observations were made.



Th e data were collected on the Raleigh International Expedition to Mauritius and Rodrigues, 1993 (Daszak 1994), the joint Kingston University, Mauritian Wildlife Foundation, Jersey Wildlife Preservation Trust, Zoological Society of London Expedi-tion, 1995 (Daszak 1996) and by Carl Jones (CGJ) and Aleksandra Maljkovic (AM).

Further information was provided by CGJ and AM on the large centipedes of Rodrigues. Th ese would have been either Scolopendra s. subspinipes or S. morsitans. Th e maximum sizes recorded for these species on Rodrigues are 115 mm and 92 mm respectively (Lewis 2002), although larger individuals of S. s. subspinipes certainly oc-cur on the island. It is probably safe to regard specimens over 100 mm long (excluding the ultimate legs) as S. s. subspinipes. Specimens less than 100 mm long may belong to either species. Th e data are given in a separate section under Scolopendra spp. on Rod-rigues. Otostigmus rugulosus Porat, 1876, is also found on Rodrigues but this is much smaller, maximum length 37 mm.

Th e purpose of the expeditions was to survey the invertebrates of Mauritius and its off shore islets. Th e fi eld observations here reported were collected incidentally; there was no specifi c methodological approach. Th e colour of specimens was recorded in the fi eld using Kornerup & Wanscher’s (1967) Methuen Handbook of Colour. Th e speci-mens collected have been deposited in the Natural History Museum, London.

Results

Scolopendra morsitans L., 1758

Distribution: A very widely distributed species: USA (Florida), Mexico, Central and South America, Caribbean, Africa, Asia, Australia, the islands of Atlantic, Indian and western and central Pacifi c Oceans. Frequently introduced. European citations are du-bious. It has been previously recorded from Round Island (Pike 1870; Bullock et al. 1979) and mainland Mauritius (Verhoeff 1939). It was collected on Île Cocos and Île aux Sables, Rodrigues in 1993 (Lewis & Daszak 1996). In 1995 the species was again collected on Mauritius, Île Cocos and Île aux Sables and on Rodrigues (Lewis 2002). Th e pre-1996 records for Round Island should be treated with caution. Th e Natural History Museum, London has a specimen of S. morsitans labelled “Scolopendra morsitans (Linn.) Mauritius 70.46”. Th is registration number in the unpublished Zoological Accessions Register An-nulosa vol. IV, 1864-1881 refers to “Round Island (nr Mauritius) collected by Sir Henry Barkly... the insects were collected by Coln Pike, US Consul.” No centipedes are listed under this registration number, so the entry is problematical. Lewis (2002) reported that three specimens (52Y, 116Y and 291Y) collected on Round Island between 31.vii.1978 and 22.viii.1978 by the Edinburgh University 1978 Expedition (Bullock et al. 1979) are S. abnormis, not S. morsitans. S. morsitans appears to be absent from Round Island. It is possible that it may have been present but has disappeared with the dramatic changes in vegetation since 1870 (Daszak 1994), or the 1870 specimens may have been wrongly attributed to Round Island as has previously been suggested for the tenebrionid beetle



Polposipes herculeanus Solier, 1848 (Gerlach et al. 1997). Th e Natural History Museum, London also has three specimens labelled “Rodriguez 76.10.” Th ey are S. morsitans. Th e accession number refers to the Transit of Venus Expedition: the specimens were presented by the Royal Society (Butler 1879).

Predators: On Mauritius, CGJ has observed the introduced toad Bufo gutturalis Power, 1927, feeding on S. morsitans and recovered a specimen of the centipede from the stomach of a mongoose Herpestes auropunctatus Hodgson, 1836.

Parasites: A faecal survey of fi ve individuals (two Île aux Sables, three Île Cocos) revealed no coccidia, other protozoa or helminths (Daszak 1994).

Food: 11.xi.1995, 21.25 hours. A specimen was observed by JDC feeding on the claw of a dead crab on the strand line on Île Cocos.

Bites: -.ix.1993. A Raleigh International Expedition volunteer on Île Cocos was bitten on the inside of the upper thigh by a red-legged morph 78 mm in length. Th e victim described a sharp pain fading to a dull throb after 10 minutes or so.

11.xi.1995. JGEL bitten on fi nger by 92 mm specimen on Île Cocos. Pain was com-parable to a mild nettle sting, lasting about an hour with very slight swelling. JGEL was also bitten by an 84 mm specimen, however this did not penetrate the skin of the fi nger.

12.xi.1995. JGEL bitten on fi nger by large specimen on Île aux Sables. Some pain for about an hour, very slight swelling.

Coloration: Lewis & Daszak (1996) observed sympatric variation in coloration in Île Cocos specimens. Th e colour of the specimens from Port Mathurin, Rodrigues, Île Cocos and Île aux Sables is given in Table 1.

Scolopendra abnormis Lewis & Daszak, 1996

Distribution: Th is species is confi ned to Round Island and Serpent Island. On Round Island, most specimens were encountered under rocks or between slabs of volcanic tuff . Th e species was particularly common in cracks in a south-facing bare rock face. Speci-mens were also found between the dead leaf bases of Latania palms. No specimens were found in 1993 in areas with good soil cover, under rocks embedded in the peat-like soil on the well-vegetated slopes or during extensive weeding of soil-covered slopes, suggesting that S. abnormis prefers crevices in rock faces or rocks with little vegetation.

On Serpent Island the species was found by PD and JDC in loose networks of bur-rows in humid peat-like soil between slabs of rock. Th e gaps between the rocks were invariably fi lled with this deposit, despite the lack of vegetation on the island. Although diurnal activity has been reported for some scolopendrids, i.e. Scolopendra heros Girard, 1853 in Texas (Neck 1985), on Serpent Island, it appears that Scolopendra abnormis is strictly nocturnal. Th e species is exceptionally common, with a population density esti-mated at greater than 12 adults per square metre under slabs of tuff . Th e Serpent Island population was estimated to be 10-15,000 (IUCN 1996).

Escape reactions: Round Island specimens remained motionless when exposed as rocks were turned. Specimens ran off when touched but did not show the violent writhing



Tab

le 1

. C

olou

r va

riatio

n of

live

Sco

lope

ndra

mor

sitan

s fro

m v

ario

us lo

calit

ies i

n Ro

drig

ues.

All s

pecim

ens h

ave

a ve

ry d

ark

trans

verse

ban

d on

the

poste

rior b

orde

r of

the

terg

ites.

Small

spec

imen

s of 5

0mm

or l

ess h

ave

a da

rk o

live

brow

n or

dar

k br

own

med

ian

long

itudi

nal b

and

on th

e te

rgite

s, in

add

ition

to th

e na

rrow

tran

sver

se

poste

rior d

ark

mar

gina

l stri

p.

Port

Mat

hurin

H

ill

ÎleC

ocos

Île aux

Sabl

es

Spec

imen

No.

11

23

41

23

46

Leng

th (m

m)

5092

8484

5085

7557

4267

Ante

nnae

ba

sal

dark

turq

uoise

copp

er re

dda

rk g

reen

dark

gre

enda

rk g

reen

blac

kbr

own

oran

ge re

dgr

eeni

sh

grey

brow

nish

or

ange

Ante

nnae

di

stal

dark

turq

uoise

viol

et g

rey

dull

viol

etda

rk g

reen

dark

gre

enbl

ack

brow

nda

rk b

lue

gree

nish

gr

eybl

uish

gre

y

Hea

dda

rk b

row

nbr

own

oliv

e bro

wn

dark

bro

wn

brow

nbr

own

brow

nbr

own

oliv

e bro

wn

brow

n

Terg

ite 1

dark

bro

wn

brow

nbr

owni

sh

oran

gebr

owni

sh

oran

gelig

ht b

row

nbr

own

brow

nish

or

ange

brow

nish

ye

llow

grey

ish

oran

gebr

own

Trun

klig

ht b

row

nbr

owni

sh

yello

wgr

eyish

ye

llow

grey

ish y

ellow

brow

nish

or

ange

light

bro

wn

yello

wish

br

own

yello

wish

br

own

grey

ish

yello

wye

llow

ish

brow

n

Terg

ite 2

1or

ange

red

redd

ish

oran

gebr

own

brow

nre

dbr

own

brow

nish

red

oran

gebr

owni

sh

red

oliv

e bro

wn

Ulti

mat

e leg

svi

vid

red

copp

er re

dbr

own

copp

er re

dbr

owni

sh

red

yello

wish

br

own

brow

nish

red

brow

nish

or

ange

brow

nish

re

dgr

eyish

ora

nge

Trun

k leg

sye

llow

ish w

hite

grey

ish re

dgr

eyish

or

ange

grey

ish

oran

gebr

owni

sh

oran

gepa

le or

ange

grey

ish y

ellow

oran

geye

llow

ish

red

grey

ish re

d



movements seen in Rhysida and Otostigmus (Lewis 1981). About 20 large individuals were kept for 24 hours in damp tissue paper in a 1.5 litre plastic water bottle at ambient temperature without showing mutual aggression, although later some captive animals were cannibalistic.

Meeting reactions: When placed in a plastic container two Round Island specimens re-acted to mutual contact by rapid recoil and running and did not show ritualised meeting re-actions such as are seen in Scolopendra cingulata Latreille, 1829 (Klingel 1960). Head on and head to tail contact between a large and a medium sized Serpent Island specimen resulted in both moving off slowly. Th ere was very little reaction in a second head to head contact.

Swimming: When two Round Island specimens were fl oated on fresh water in a plastic container, they sank, slowly fl exing the body. Th ey neither swim as does S. subspinipes (cf. Lewis 1980) nor walk under water. A Serpent Island specimen in fresh water fl oated on the surface with some movement for 6 minutes, then sank showing sporadic movement but mostly motionless. Th e specimen recovered on removal after a further 50 minutes. Two specimens sank in sea water, thereafter showing sporadic movement and were then stationary.

Predators: A large specimen dropped at camp on Round Island was immediately seized by a Telfair’s skink (Leiolopisma telfairii Desjardins, 1831). Vinson (1975) found centipede remains in the alimentary tract of a Serpent Island night gecko Nactus serpensin-sula (Loveridge, 1951) (probably a Round Island specimen). Daszak (1995) reported presence of oocysts of a new species of Adelina (Daszak & Ball in prep.) in the faeces of N. serpensinsula durrelli Arnold & Jones, 1994, collected on Round Island. Adelina sp. parasites are usually host specifi c, and so this pseudoparasitism suggests that S. abnormis forms part of the Nactus sp. diet.

It is not known whether N. s. serpensinsula takes S. abnormis, however it is the only nocturnal reptile on Serpent Island and feeds on a wide range of invertebrates. Since S. abnormis is nocturnal and there are few other large invertebrate species present on Serpent Island (no cockroaches were collected), it is likely that the gecko relies on the centipede for a major part of its diet.

Parasites: Oocysts of a coccidian (Adelina sp.) and a gregarine parasite (Grebnick-iella sp.) were found repeatedly in faecal samples from S. abnormis (Daszak & Ball in prep.). Th e prevalence of Adelina sp. oocysts in faecal samples was high: 68% (n=22) for Round Island centipedes, 100% (n=15) for Serpent Island specimens. All animals were collected during the winter period, August-September 1993 and November 1995. Following prolonged captivity in small groups at high population densities on Round Island, all individuals were infected. Th ese animals showed swelling of the abdomen, paralysis of the hind limbs and some became moribund. Histological section of the gut showed large numbers of the endogenous stages of a new species of Adelina within the host cells and trophozoites of the gregarine within the gut lumen and it appears that the high intensity of infection by these parasites caused the clinical signs observed. Ball et al. (1995) found similar clinical signs in captive Malagasy hissing cockroaches Gromphadorina portentosa (Schaum, 1853) which were kept in high population densi-ties and were heavily infected by gregarines. Th ey concluded that the parasites caused



fatal disease due to increased transmission rates in the high population density captive conditions. No other pathogenic agents were identifi ed in S. abnormis.

Food: On Round Island, CGJ observed a specimen feeding at night on a soft, white newly moulted cockroach. Specimens collected by CGJ in 1995 for captive breeding were fed on chick legs. At the Zoological Society of London captive individuals were fed on an artifi cial meat diet and readily took crickets (P. Pearce-Kelly, D. Clarke pers. com.).

On Serpent Island, an individual was observed (at 21:00 hrs on 5.xi.95 by JDC and PD) feeding on the pectoralis muscle of a partially dried out dead tern chick. Large num-bers of centipedes were observed roaming the common noddy, Anous stolidus L. 1758, lesser noddy A. tenuirostris (Temminck, 1858) and sooty tern Onychoprion fuscatus (L., 1766) nesting sites during the night, presumably foraging.

Bites: -.viii.1993: PD bitten by a large Round Island specimen. Th e bite was instantly painful swelling up to a small (c. 0.5 cm2) pale raised area with loss of tactile sensitivity in the aff ected area. Th e pain wore off after around ten minutes, however the aff ected area remained slightly swollen for 2 days with a dull pain and slight loss of tactile sensitivity.

2.xi.1995: Sheila Lewis bitten on fi nger by large Round Island specimen. Slight swell-ing and painful for about one hour. No gross tissue damage.

3.xi.1995: PD bitten on fi nger by large Round Island specimen. Slight swelling, pain-ful for one and a half hours. No gross tissue damage.

Coloration: Th e colour of four live Round Island specimens 60, 66, 75 and 82 mm long was antennae, basally pale yellow to light brown, distally greyish green to greyish turquoise. Head brownish yellow, trunk yellowish brown, posterior border of tergites to-bacco brown. Ultimate legs brownish yellow or reddish golden. Trunk legs greyish yellow or light yellow tinged greyish green. Th e colour of three live Serpent Island specimens 78, 78 and 95 mm long was antennae greyish yellow or orange yellow, distally greyish yellow to olive brown. Head and trunk olive brown. Ultimate legs orange or brownish orange. Last three pairs of legs tinged blue. Trunk legs pale yellow to greyish yellow.

Scolopendra subspinipes Leach, 1815

Distribution: Scolopendra subspinipes is a very common large species with several sub-species, it is widely distributed and frequently introduced. It is found on some Atlantic islands; Central America, the Caribbean Islands and Brazil; India and the islands of the Indian Ocean, SE Asia, through China to Japan and eastwards to Hawaii; there are a few scattered African records. In the western Indian Ocean it is present on Rodrigues. St Brandon (Raphael Island), the Seychelles, Comoros and Madagascar (Lewis 2002). Specimens of the nominate subspecies were identifi ed from Réunion by Kraepelin (1904) but the species is now apparently absent from the island since it was not known to the local naturalist Jean-Michel Probst nor to the entomologist Christian Guillermet (pers. com.). Both were familiar with S. morsitans which they claimed was their largest species. Kraepelin (1904) also identifi ed specimens of S. s. subspinipes from Mauritius (Île de France) but it is now absent. Until recently it was common throughout Rod-



rigues and was the most common large centipede on the island (personal observations) but is absent from Île Cocos and Île aux Sables (Lewis 2002).

Coloration: Th e colour of two live specimens of S. s. subspinipes, length 65 and 85 mm, from the hill above Port Mathurin, was recorded. Antennae: basally greyish yel-low, distally bluish grey or basally red and distally brownish orange. Head brown or red brown, trunk olive brown or dark brown, ultimate legs brownish red to reddish brown, trunk legs red or brownish orange at base, distally bluish grey. Th e trunk tergites with posterior border and a narrow strip on the lateral margins very dark grey/black.

Scolopendra spp. on Rodrigues

Predators: Centipedes preyed upon by feral cats: AM collected 57 feral cat faecal pellets from Île Frégate. Large centipedes comprised 70-80 per cent of faecal material by volume and were present in 54 of the pellets. Th e abundance of centipedes in the diet may have been due to an acute shortage of food. In addition to a few crickets, a locust, some bone fragments and a small bird, the faeces contained a lot of grass and a few seeds. CGJ found centipede remains in cat scat from Solitude, Rodrigues in April 2000. Haltenorth & Diller (1977) reported that the wild cat Felis silvestris Schreber, 1775 of Europe, Africa and parts of Asia eats centipedes.

Many people keep chickens around their houses because they feed on the centipedes and are presumed to reduce populations. We received one record each for a musk shrew Suncus murinus (L., 1766) eating a centipede about 75 mm long in January 1999 and of an agamid lizard Calotes versicolor Daudin, 1832 “fi ghting” with a centipede whilst attempting to consume it. Mauritians and Rodriguens do not tolerate centipedes and tend to kill them at every opportunity. One informant said that as a young child, he and his friends would roast centipedes over an open fi re and eat the fl eshy bodies.

Food: Th e large centipedes of Rodrigues are formidable predators that will catch a wide range of living prey, sometimes many times their own size. CGJ kept individuals of S. subspinipes in captivity that fed on house geckoes (Hemidactylus frenatus Duméril & Bibron, 1836) and cockroaches, which they actively pursued and killed. Captive indi-viduals also readily feed on carrion. Large centipedes were reported by informants to feed regularly on house geckoes and cockroaches in houses. Th ey also feed on fl ying insects attracted to lights at night. We were given single records of a centipede feeding on a large house spider and on the juice oozing from a ripe mango. Several informants mentioned that the centipedes kill and feed on day-old chicks, which usually weigh around 20g. Individuals feed readily upon carrion and are attracted to the smell of fi sh and fl esh. If frozen fi sh is left to defrost outside, it fairly rapidly becomes infested with centipedes. Th ey are particularly attracted to strong smelling fi sh such as unicorn fi sh Naso brevirostris (Valenciennes, 1835) and to chicken, especially the viscera. Manton (1964) considered that in addition to catching and eating living prey scolopendrids are also scavengers. Opinion varies as to whether they can detect prey from a distance (Lewis 1981), however the observation reported above shows that, at least, some species are able to.



Bites: CGJ and AM have spoken to many people who had been bitten by centi-pedes, most of whom had been bitten many times. Th ere was good agreement between informants on the nature of bites. All agreed that bites can vary a great deal in intensity, some being very painful (more so than a wasp sting), others less painful, but always subjectively worse than a pin prick. Th e severity of bites may be greater if the centipede is protecting young, or has been injured in an attempt to kill it. Sometimes distinctive puncture wounds are left. Most reports were of people bitten on the arms, hands or buttocks (after sitting on a centipede). Bites during the night are common, while the victims are sleeping, either on the face, eyelids, lips of ears with two records of bites on the penis (one of these records from Aride, Seychelles). Bites around the mouth have been reported when the victim had previously been eating fi sh and had not thoroughly washed his/her face. Typically, the area around the bite swells and reddens markedly, with the swelling lasting for one or two days. Bites to the eyelid may make the lid swell so much that it closes the eye. Th e area around the bite itches for about 3-4 hours or up to 6 hours and may go numb.

People react to these bites to a variable degree, some are hardly aff ected, but for others it may have serious consequences. Following a bite to the face of one informant’s father, his whole head swelled and he developed a fever, with high temperature and aching throughout the body. Th e patient was hospitalised for fi ve days and during this period around 20 pustules erupted on his face. Informants reported that the eff ects of centipede bites may be neutralised by rubbing the bite with onion, garlic or by urinat-ing on it. Bites may leave visible scars: the Head of Fisheries (Mr. Clarel Begue) and his wife were woken up by their baby daughter’s screams one night and found a large centipede had chewed a small hole in, and allegedly was feeding on, her forehead. She was about two years old at the time and still had the scars almost 15 years later.

We were generally told that centipede bites were not fatal, but two informants said that they each heard of a person dying following a centipede bite; a young boy and a priest, but were unable to provide specifi c details. Th e only case with any supporting details (verifi ed by offi cials from the Ministry for Rodrigues) was of a centipede causing the death of a soldier during the period when the current offi ce/fi eld station building at the Forestry Quarters at Solitude, Rodrigues was the Special Mobile Force (SMF) headquarters. Rainwater was collected from the roof for drinking and this was piped into a large concrete tank at the back of the house. An offi cer took some water to drink without examining it fi rst and was bitten in the back of the throat by a relatively small centipede and as a result died, perhaps of asphyxiation.

Discussion

Origins, distribution of Mauritius and Rodrigues scolopendrids

Th e distribution of S. abnormis resembles that of some endemic reptiles. Rock-dating indicates that Mauritius was formed by volcanic activity between 7.8 and 6.8 million



years ago, the last volcanic activity being 100,000 years ago (McDougall & Chamalaun 1969). Round Island and other islets (including Serpent Island) are on the same sub-marine plateau 30-55m below current sea level and must therefore have been attached by land bridges to Mauritius after sea level lowering during ice ages.

It seems likely that the ancestor of S. abnormis colonised Mauritius during the last few million years, reaching the outer islets by rafting or crossing ice age land bridges. After the last ice age, the rising sea-levels isolated the Serpent and Round Island popula-tions from the mainland (and each other), giving an historical distribution similar to those presumed for Scelotes bojeri Desjardin, 1831, and other off shore island endemic reptiles (Jones 1993). Th at is a distribution throughout the mainland and the off shore is-lets of Gunner’s Quoin, Flat Island, Round Island and Serpent Island, but now confi ned to the off shore islets probably being eliminated from the mainland by introduced preda-tors. Th e introduced common and ship rats Rattus norvegicus (Berkenhout, 1769) and R. rattus (L., 1758), the musk shrew Suncus murinus and the wolf snake Lycodon aulicus (L., 1758) are thought to be largely responsible for the elimination of ground-dwelling lizards from the mainland (Arnold 1980; Cheke 1987; Jones 1993). Shrews are known to take centipedes (Dickman 1995) and for some species chilopods make up the major-ity of their diet (Castien & Gosalbez 1995). S. abnormis may have been outcompeted by introduced S. morsitans on the mainland, although the possibility that S. morsitans once occurred on Round Island cannot be ruled out. If this was the case, the dramatic changes in vegetation that have taken place on Round Island since the mid 19th century (Daszak, 1994) may have favoured S. abnormis (which appears to prefer rock crevices) and rendered the habitat unsuitable for S. morsitans. Th e steady increase in vegetation re-sulting from conservation measures could, conceivably bring about a reduction in the S. abnormis population. Th e species is very abundant on Serpent Island, which may never have been vegetated during the current post-glacial period.

Scolopendra subspinipes is very widely distributed and common on Indian Ocean islands (see above). Lewis (1988) observed that it appeared to be a wandering species and that its behaviour favoured distribution through trade. Th ere are old but reliable records from Réunion and Mauritius but it now appears to be absent from these islands.

Th ere are three potential predators on Mauritius which could be responsible for the disappearance of S. s. subspinipes, none of which were present on Rodrigues until very recently. Th ese are the musk shrew Suncus murinus (introduced before 1773), the tenrec Tenrec ecaudatus (Schreber, 1777) (introduced in the late 18th century) and the toad Bufo gutturalis Power, 1927 (introduced 1922). S. subspinipes is apparently now absent from Réunion where there are the same three predators.

Th e precipitous population decline of large centipedes on Rodrigues

Th e large centipedes on Rodrigues (both S. morsitans and S. s. subspinipes) and a large black fi eld cricket Gryllus sp. have all shown a precipitous decline which coincides with the introduction and spread of the musk shrew. Th e musk shrew recently reached



Rodrigues and has shown an explosive population growth. Th e fi rst records that we are aware of were from the capital Port Mathurin in 1997. AM observed a population ex-plosion around the Forestry Quarters at Solitude in July and August 1998, it was wide-spread by late 1998 and CGJ found one in Anse Quitore, Plaine Corail in Feb 1999 and by late 1999 they were all over the island in high densities. Subsequently the large centipedes (S. s. subspinipes and S. morsitans) common in houses at night have become rare, as have large centipedes everywhere on the island. In October 1998 large centi-pedes were still common in the cave Cavern Botteille on Plaine Corail a sink hole with water at the bottom where shrews could not easily enter. In 1999 large centipedes were very rare on the main island of Rodrigues but could still be found on Grande Mon-tagne in small numbers and were still common on some of the small satellite islands none of which yet have shrews. Th is suggests that it is the shrew that is responsible for the decline of large centipedes on Rodrigues although all local informants stressed that the centipedes had disappeared due to predation by the “Chemeleon” the agamid lizard Colotes versicolor Fitzinger, 1826. Th e agamid was introduced to Quatre Vents in the mid-1980’s was widespread a decade later and was a common lizard everywhere by the late 1990’s. Th e decline of the centipedes and crickets however correlate far better with the explosive increase in shrew numbers than they do with the increase in agama lizards. Most informants did not believe that the centipedes had shown an island-wide decline in numbers and erroneously felt that there were still plenty in the forest.Th e population explosion of the musk shrew on Rodrigues has many similarities with the population explosion of this species on Guam where it covered the whole island (54,100 ha.) in fi ve years. On Guam the shrew has been implicated in the decline or extinction of several species of lizard and an order of magnitude decline in house mice (Mus domesticus Rutty, 1772) (Fritts & Rodda 1998). Th e musk shrew is clearly highly invasive and predatory and may have serious impacts upon oceanic island ecosystems by direct predation and by disrupting trophic interactions.

Biological diff erences between Round Island and Serpent Island populations of S. abnormis:

Scolopendra abnormis from Serpent Island are somewhat larger and possibly slightly diff erent in coloration from the Round Island population. Th e presence of many ju-venile specimens on Round Island but not on Serpent Island in early November 1995 suggests a diff erent phasing of the life histories (Lewis 2002). Similar diff erences occur between the Round and Serpent Island populations of the skink Scelotes bojeri and the gecko Nactus serpensinsula (Jones 1993; Arnold & Jones 1994). However in the case of the reptiles, signifi cant morphological diff erences have led to separate populations of the gecko being given subspecifi c status (Arnold & Jones 1994) and it is thought that the Serpent Island populations of the skink may also represent a separate subspecies (Jones 1993; Arnold pers. com.).



Th e reasons for the high population density on Serpent Island may be abundant food in the form of a plentiful supply of dead adults, chicks and perhaps broken eggs of the common and lesser noddy and the sooty tern. With a far higher nesting sea-bird population on Serpent Island than Round Island, the sheer biomass available for S. abnormis would allow a much denser population of centipedes there. One of the costs of this higher population density may be an increased prevalence of infection by faecal-orally transmitted parasites (100% vs. 68% for Serpent vs. Round Island). For-manowicz & Bradley (1987) demonstrated experimentally that increasing prey density causes a rapid, reversible change in Scolopendra polymorpha Wood, 1861, behaviour from active foraging to ambush-like tactics. Despite high food availability for Serpent Island S. abnormis, it remains an active forager, which may suggest that carrion rather than invertebrates is the major food source.

Colour diff erences between Serpent and Round Island specimens of S. abnormis are given above. Such diff erences may perhaps be genetic, but nothing is known of the causes of colour variation in the scolopendrids – colour is very variable in some species as, for example, in the populations of S. morsitans on Île Cocos and Île aux Sables and stable in others (Lewis 2003). It may change with age (Lewis 1968).

Conservation prospects for S. abnormis: It appears that the populations of S. abnor-mis on Round and Serpent Island may be relicts of a mainland species and as such should be considered a population reduced by human impact. However, the popula-tions on Round (151 ha) and particularly Serpent Island (20 ha) appear overtly healthy and not in immediate danger of extinction although, as mentioned above, changes in habitat due to conservation measures on Round Island could adversely aff ect the popu-lation there. Th e fi rst priority in developing a conservation strategy for this species was to assess its distribution: the species appears to be limited to these two islets (Lewis & Daszak 1996; Lewis 2002). Even without precise population estimates, this restricted distribution has led to their classifi cation as Vu, D2: “vulnerable” with a “restricted distribution” and “susceptible population” on list 1 of the IUCN red list (IUCN 1996). Th e most obvious threat to populations on both Serpent and Round Island is introduc-tion of a potential predator, such as the musk shrew. However this is unlikely to occur on Serpent Island due to its remoteness and lack of landing sites, or on Round Island due to the more intensive monitoring for introductions.

Captive breeding programmes have been set up for a number of high profi le in-vertebrate species (e.g. partulid snails – Pearce-Kelly et al. 1995) and a case can be put forward for captive breeding of S. abnormis using the same criteria by which the skink Leiolopisma telfairii (Desjardin, 1831) (a species confi ned to Round Island but fairly abundant there) has been brought into captivity. Extinction of island dwelling centipedes has occurred previously: two species of Galapagos centipede are thought to have become extinct during this century (Shear & Peck 1992), one was the scolopen-drid Cormocephalus andinus (Kraepelin, 1903) a common South American species. Th e centipede Cormocephalus coynei Koch, 1984 is a very large but rare species confi ned to the 260 ha Philip Island (near Norfolk Island) in the South Pacifi c where vegetation has been severely degraded by the action of introduced pigs, goats and especially rab-



bits, and most of the topsoil has gone (Koch, 1984). Th e current status of C. coynei is unknown.

Eight specimens of S. abnormis were taken from Serpent Island (the type locality) and four from Round Island in 1995 for captive breeding at the Zoological Society of London. However, after 3 years in captivity, all died. Parasites were isolated from some of these animals but the causes of death are unknown.

Acknowledgements

Th e 1995 expedition was funded by Th e Oryx 100% fund of Fauna and Flora Internation-al, the Royal Geographical Society, Leica Cameras (UK) Ltd and Kodak Ltd. Fieldwork was also supported by Th e Linnean Society of London Appleyard Fund. JGEL received grants from the Percy Sladen Memorial Fund and the Natural History Museum God-man Exploration Fund. We thank Mr Yousoof Mungroo, Govt. of Mauritius; Mr. Hugo Meunier, Head of Forestry, Rodrigues; Claude (Roland) Raboude, Richard Payendee, Mary-Jane Raboude, Arnaud Meunier, Alfred and Anieta Shan-Yu, Kirsty Swinnerton and Pierre de Boucherville Baissac (Mauritian Wildlife Foundation); George Pierre-Louis and Pierrot Pierre, Rob and Vicki Lucking; Quentin Bloxam and John Hartley (Durrell Wildlife Conservation Trust); Simon Tonge, Paul Pearce-Kelly, David Clarke and Elspeth Chaplin (Zoological Society of London); Brian Bell, Mike Bell and Jos Bhuiyan (Wildlife Management International, New Zealand); Jonathan Cook, Jock Marfell, Roger Jackson, Warwick Jacobs and numerous volunteers on the 1993 Raleigh International Expedition to Mauritius and Rodrigues; Ralph Manly and Stanley J. Ball (Kingston University, UK); Paul Hillyard (the Natural History Museum, London). Our thanks are also due to Pavel Stoev and Marzio Zapparoli for their helpful comments on the manuscript.

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