Table Of ContentArachnol.Mitt. 34:27-38 Nürnberg,Dezember2007
An unidentified harvestman Leiobunum sp,alarmingly invading Europe
(Arachnida:Opiliones)
HayWijnhoven,Axel L.Schönhofer&Jochen Martens
Abstract:Sinceabouttheyear2000a hitherto unidentified speciesofthegenusLeiobunumC.L.Koch,1839,
has rapidly invaded central and western Europe.Records are known fromThe Netherlands (probablythe
countryoffirstoccurrencein Europe),Germany,AustriaandSwitzerland.Thisintroducedspecies,until now,
mainlyinhabitswallsofbuildingsand rockyenvironments.Adultscharacteristicallyaggregateduringday-
timeintogroupsofupto 1.000individuals.Thespeciesisdescribedanddetailson its presentdistribution,
habitatpreference,phenologyand behaviourarepresented.
Keywords: aggregation,alien species, behaviour, central Europe, introduced species, invasion strategies,
taxonomy
It is not at all common practice to publish on a ofsimilarly sized and coloured specimens turned
species that has not yet been identified to species up on a German SpiderWebsite (http://spinnen-
level.Inviewofthefactthatanunknownharvestman forum.de/forum). Some specimens from a town
of the genus Leiobunum C. L. Koch, 1839 has in Saarland, Germany, were collected and they
recently not only been found for the first time in perfectly matched the Dutch species. More
theNetherlands,butalsoinGermany,Austriaand sightings were published through this website,
Switzerland-regularlyoccurringin astonishingly one ofwhich originated fromAustria.
large numbers - it seemed useful to publish on Thefactthatanapparentlyintroducedharvest-
this matter as soon as possible. Undoubtedly this man species has already succeeded in colonizing
introducedspecieshastheabilitytobecomeathreat parts ofWestern and Central-Europe, combined
to ourindigenous opilionid fauna. with the sightings ofhuge aggregations, gave rise
to our concern. In the near future this invasive
Some blackish specimens ofthe genus Leiobunum speciescouldverywellbecomeathreattonumerous
(Fig.1)werefoundinOctober2004nearNijmegen, indigenous harvestman taxa.
The Netherlands. With the key provided by From2004onward,attemptsweremade toget
MARTENS (1978) these specimens could not be thisLeiobunumidentified,bystudyingtheavailable
identified as a north-western or central European literature and bycontacting several specialists (see
species, nor were we able to assign it to any Acknowledgements). One of the difficulties one
European representative of the genus known to meets with is the worldwide distribution of the
date. During the following years, 2005 and 2006, current genus Leiobunum. About 125 species have
many more records were obtained from several been described until now from Asia (especially
localities near the river Waal, in the vicinity of Japan), Europe, Northern Africa, North and
Nijmegen. At two industrial sites this mysterious Central America (CRAWFORD 1992,TOURINHO
harvestman occurred in extremely large numbers, 2007).Moreover,manyoftheoriginaldescriptions
making it all the more urgent to identify it to the are inadequate compared to modern standards.
species level. In 2007 this Leiobunum species was Until now only the central European (MARTENS
found near Amsterdam. Simultaneously photos 1978),theJapanese(SUZUKI 1953,1976)andpartly
theNorthAmericanspecies(BISHOP1949,DAVIS
HayWIJNHOVEN,coordinatorsectionOpiliones,EIS- 1923)havebeenrevisedandcanberecognizedfrom
Nederland,EuropeanInvertebrateSurvey,Leiden,The A
Netherlands,E-mail:[email protected] the descriptions and figures alone. worldwide
AxelL.SCHÖNHOFER&JochenMARTENS,Institutfür revision ofthe genus has notyetbeenundertaken.
ZoologiejohannesGutenberg-UniversitätMainz,Abt. We started our research on the possible origin of
GSyesrtmeamnayt,isEc-mhaeilZ:ooslcohgoieen;hMo@üsltluedrewnetgs.6;unDi--5m5a0i9n9z.Mdaei;nz, this species in Spain and Northern Africa, and
[email protected]. then shifted attentiontoMexico and the southern
28 H.Wijnhoven,AI.Schönhofer&J.Martens
partsoftheUnited States. Stilltheeffortsofmany DescriptionofLeiobunum sp.
personsprovedfruitless.Alsotype seriesofvarious Fieldidentification
Leiobunum species deposited in the Senckenberg Leiobunum sp. is a large species, similar in size
Museumwere investigated (seeAppendix).Afirst to Leiobunum limbatum L. Koch, 1861, long-
shortnoticereferringto this specieswaspublished legged, robust, body almost blackish with only
byWijnhoven (2005). a few light markings and with a slightly green
Inthiscontributionwedescribethemorphology metallic shimmering dorsum (Figs. lc-d). There
ofthis invasive species ofthe Leiobuninae,which is only minor sexual dimorphism in coloration
we will name here provisionally as Leiobunum and dorsal pattern. Ventrum and coxae of the
sp., summarize the currently known records, and legs are warm pale yellowish to pale light brown,
give some information on the habitat, phenology, strongly contrasting with the dark trochanters,
behaviour and accompanyingharvestman species. legs and dorsum.The legs are conspicuouslylong
and slender, dark brown to black (Figs. la-b). In
Fig.1:Leiobunumsp.;a-b:aggregationsofadultindividuals,TheNetherlands;a:onabrickstonewall,Ooij;b:ontheceilingof
anold building,Beuningen;c-d:adults,Witten/Ruhr,Germany;c:c?;d: 2;2ndrecord inGermany.-Photos:a,b:H.W.,c,d:
A.Steiner.
UnknownLeiobunumspeciesinvadingEurope 29
females the tibiae of the legs have conspicuous Venterandcoxae (Fig. 2f): armed with hairs, light
white tips, reduced in older specimens (Fig. lb). yellowtopaleorange,contrastingstronglywithTr
Large aggregations numberingdozensupto many and dorsum; anal operculumwhite, similar to the
hundreds of long-legged harvestmen on house jointmembranes between Cx andTr (Fig. 2n).
walls undoubtedly point to Leiobunum sp. This All Cx with a well developed frontal and
characteristic species cannotbe confusedwith any posterior row of tubercles (Figs. 2f-g), posterior
ofthe central EuropeanLeiobunum species. rowoflegthreemissing,resultingincoxaldenticle
formula:FB FB F- FB (F=frontrow,B=backrow).
Description Genital operculum armed with scattered hairs; a
We use the following abbreviations (for singular rowofeight to ten denticles on its lateral margins
and plural): Ceph cephalothorax, Cx coxa Mt (Figs.2h-i).
metatarsus, Pt patella, Ta tarsus, Ti tibia, Tr Pedipalpus(Figs.3a-c):Fearmedvewitharowof5
trochanter,veventral,ventrally. to 7large,blunt tubercles and meso-vewith arow
Tab.1:Lengthsoflegs1-IV(in mm),3,inparentheses '? (afterspecimensfromOoij,TheNetherlands)
Tr Fe Pt Ti Mt Ta
I 0,4(0,4) 11,8 (10,5) 1,6 (1,7) 9,4 (8,5) 12,1 (11,0) 15,6 (15,4)
II 0,4(0,4) 18,0 (17,0) 1,7(1,6) 17,1 (16,3) 17,2 (20,0) 35,3 (22,8)
III 0,4(0,4) 12,0 (10,4) 1,9 (1,6) 9,3 (9,4) 13,3 (11,9) 17,4 (16,0)
IV 0,4(0,4) 15,5 (14,0) 1,9 (1,8) 12,2 (11,0) 18,5 (16,0) 24,3 (21,2)
mm
Male: Length of body: 4.0-4.9 (n=5); ofblack-tippeddenticles; distallyatthe median as
maximum spread oflegs: about 180 mm. well as the lateral sidewith some denticles; on the
External morphology: The scutum is of the type innerproximal sidewith 1 to 3 blacktubercles. Pt
‘scutum parvum’ (compare MARTENS 1978, Fig. with small tubercles dorsally and laterally; Ti ve
5), with a finely granulated dorsum. Complex withscatteredtubercles;Taquiteshort,onlyslightly
microsculpture, consisting of star shaped curvedinward,vewitharowof1 to8black-tipped,
granulations and finely sculpted ripples (Fig. lc). short spines. Pedipalpus pale,yellowish, the apical
AttheanteriorpartoftheCeph,infrontoftheeye dorsal portion ofthe Fe clouded with brown, Pt
tubercle, the granulations are somewhat irregular, dark brown, lighter ve, Ti dorsally clouded with
partlyfaded,partlyarrangedinripples.Atthelateral brown.
sides ofthe dorsum the granulations are faded. Chelicerae (Figs. 2k-m): smooth and glossy, no
Colorationofdorsum: dark brown to partly black, tubercles present, only armed with small setae,
inlifewith a metallicgreen shimmer, as ifcovered uniformlyyellowto pale orange.
with a thin oilycoating (Fig. lc).This gloss is lost Legs (Figs, la-c, Tab. 1): conspicuously long and
in alcohol,unless the specimenisleftto dry. Some slender, dark brown to black, in some 88 with
88 arelighter(muchmoreobviousinalcoholthan lightertipsatthejoints,especiallyatthetipsofthe
inlivespecimens,partiallyduetotheabsenceofthe second and fourth leg, its extent often depending
overlayinggloss),withgoldenbrownpatchesatthe on age after maturation.Trdarkbrownwith some
sides ofCeph,occasionallyextendingonthedistal lightermottling.
part of abdomen, showing an indistinct central Penis (Figs. 2a-e): long and slender, seen dorsally
marking.Sometimestheabdominalsegmentshave the truncus tapering from base to the glans,
regularlypositionedbrownspotslaterallyandpairs slightlybroadeningagainbelowthepockets ofthe
ofbrown spots on the central marking. alate part; alate part markedly longer than broad,
Eyetubercle:high,constrictedbasally,canaliculate, somewhat broadening from the middle section to
slightlytiltedbackwards,andarmedonlywithafew the top;distalpartalmostrectangular. Extremetip
very small hairs. The eye tubercle is glossy black, of the stylus with a characteristic small bulbous
brownishatthe anteriorbase.Insome 8 8 ithas a projection dorsally (Fig. 2e). When seen exactly
slightlylighter, more orless distinctbrown central from the front, the transparent membranes at the
midline. top ofthe alate part intersect. Alate part strongly
30
H.Wijnhoven,AI.Schönhofer&J.Martens
;
UnknownLeiobunumspeciesinvadingEurope 31
flattened in lateralview. Seen laterallythe pockets Legslongandslender,generallyslightlyshorter
of the alate part appear bulbous-shaped at their thanin S thesecondlegmeasuringabout80mm.
;
base,narrowingtothetop,formingadistalopening Legswithconspicuouswhitetipsatthejoints,most
withaseparatedorsalandaventralmembrane(Fig. distinct at the Ti tips oflegs II and IV but often
2c, arrows). reduced in older specimens.
mm
Female: Length of body (in mm): 5.4-6.4 Taxonomy
(n=5); maximum spread oflegs: about 170 mm. In general the penis shape of Leiobunum sp. is
Externalmorphology(Fig. Id): scutum ofthe type similar to that ofLeiobunum rotundum (Latreille,
'scutum parvum', expressed as a stiff, granulated 1798), L. defectivum Rambla, 1959 (according
&
'shield' once the eggs have started to develop to figures in PRIETO FERNÄNDEZ 2007), the
and the body is somewhat enlarged and inflated. North American species L. nigripes Weed, 1892
Colorationasinthe S butwithmoredistinctlight andL. ventricosum (Wood, 1870) accordingto the
,
markingsattheCephandabdomen,revealingadark drawings in BISHOP (1949). But this similarity
browncentralmarkingwithsmallregularlyspaced maynot necessarilyindicate close relationships.A
light brown to yellow spots on each abdominal shimmering dorsum, even more intense than that
segment confined to the lateral margins; central ofLeiobunum sp. is also present in the Mexican
marking frequently terminates in two black, non- species L. metallicum Roewer, 1932, but its penis
shiny,sidewayspointed,triangularspots.Dorsumin shape is very different. Until nowwe were unable
livespecimenswithametallicgreenshimmer(Fig. to trace avalid name for this species.We checked
Id) similar to that ofthe d; membranes between the type series of26 Leiobunum species housed in
and at the sides ofthe tergites greyish; coloration the Forschungsinstitut Senckenberg, Frankfurt
oftheventerstronglycontrastingwiththedorsum, am Main; we conclude none matches the present
beingpaleyellowto pale orange brown,ingeneral species (seeAppendix).
slightlymore orange than in 88
.
-
Fig.2:Leiobunumsp.;6 a-e:genitalia;a-b:penis,dorsalview,c-d:penislateralview;e:distalpartofglansandstylus,lateral
view;f-g:firstrightleg,frontalviewofCx,Trand FeanddetailofdenticlesofCx;h-i:genitaloperculumanddetailof
denticles;k-m:chelicera,k:left,lateralview,I:right,medianview,m:enlargedventralspur;n:analoperculum.-©H.W.
32 H.Wijnhoven,AI.Schönhofer&J.Martens
PresentdistributioninEurope Leiobunum were recorded from its walls between
About 130 specimens were collected; voucher August4 and October 7,2005 (Fig. Id).
specimens are deposited in Coll. J. Martens In2006 thespecieswasfoundinthevicinityof
(CJM) No. 5315, 5469, 5978-5985, 5988, 6003, abrickstonefactorynorthoftheriverWaal,andat
6009, 6038: 39 86, 23 $ $ 286 and 3$ 9 in several similarlocations west ofNijmegen aswell.
;
Coll.Naturalis,NaturalHistoryMuseum,Leiden, At one particular site the species also occurred
The Netherlands; 1 8 1 9 in Coll. C. Komposch, in huge numbers (Figs. la-b). The owner ofthis
Graz,Austria;2 88 1 $ inColl.C.Prieto,Bilbao, companysaidthishadbeengoingonforfourtofive
Spain;2 88, 1 9 in Coll.J. Shultz, College Park, years now.Atthewhitewalls ofhis adjacenthouse
USA. The following account lists the confirmed one could observe many dense aggregations each
records up to October2007 (Fig. 4). containing hundreds ofthese darkharvestmen.
Additional records in 2007 confirmed this
TheNetherlands Leiobunumhasbynowcolonizedlargeparts ofthe
The first record ofLeiobunum sp. is from October regioninthedirectvicinityoftheriverWaal.Until
19,2004.A 8 and 9 were collected on a concrete October 2007 it was found in the villages: Spijk
construction on a dike in Ooij, east ofNijmegen, (near Lobith, N: 51°50' E: 6°8'), Ooij, Bemmel
provinceofGelderland,theNetherlands(N:51°51' (N: 51°54' E: 5°53'), Beuningen (N: 50°52' E:
UTMGT
E:5°56', 0249).Itislocatedbetweenthe 5°46'), Deest (N: 51°53' E: 5°40') and Druten (N:
riverWaalandalargeindustrialsite.OnOctober20 51°52'E:5°37',allleg.orvid.HW).Themaximum
a 8 and 9 specimenwere collectedfromthe same distancebetweentherecordingsitesinthevicinity
spot, on November 3 another 8 (HWleg.). ofNijmegen is 40 km.
In2005permissionwasgrantedtovisitanearby The first evidence thatthis species alreadyhad
industrial site. An old disused brickstone oven to be more widespread inThe Netherlands was a
functions as a storage building. Hundreds ofdark recordin2007inWestzaan(N:52°28'E:4°46'),not
farfromAmsterdam,where somedozensoccurred
on the walls of a house. Matty Berg collected 3
subadult specimens onJune 2, 2007, one adult $
onAugust 13,2007 (all Coll. HW).
Germany
Nordrhein-Westfalen,Witten/Ruhr(N:51°26'E:
7°20',TK4510),one 9 restingonashadedwallsur-
roundingagardenarea,wasnoticedbyAxelSteiner
on September 21, 2006. Based on photographical
evidence ofa single 9 this observation represents
the firstrecord in Germany.
TK
Hagen, near Breckerfeld (N: 51T6' E: 7°27',
4710), on November 8, 2006 the second record in
Germany was noticed by Axel Steiner, based on
photographical evidence. He found one 6 on the
wallofanoldhistoricalbuildinginasmallforested
valleywithacreek.OnOctober13,2007henoticed
15-20 specimens on the wall of a closed down
factoryin Hagen (CJM 6038: 388,29 9).
Essen (N: 51°24'37" E: 7T52", TK 4508), rem-
Fig.4:PresentdistributionofLeiobunumsp.incentral Europe nants ofcastle Isenburgsituatedwithin the exten-
uptoDecember2007. ded city forest protected area; first recorded July
NL:a:Westzaan,b:vicinityofNijmegen;D:c:Essen,d: 19, 2007 by Jörg Ramsauer, then visited several
Witten,e:vicinityofHagen,f:Mayen,g:Enkenbach- times from September to December 2007 by Ka-
ALlasuesnebno;rAn:,I:hL:aSuataerrlaocuihs.,i:vicinityofSaarbrückenCH:k: rolaWinzer. On one occasion severalgroups ofin
UnknownLeiobunumspeciesinvadingEurope 33
totalabout570 specimenswere countedviadigital 2007 two 9 9 specimens ofLeiobunum sp. were
photographsonthewallsoftheoldmassivegateway recorded and collected by Aloysius Staudt. No
(CJM 5978: 566). The population trend at this further specimens were present; no aggregations
locality is shown in Fig 5. Continuous decline in at the walls of this house or adjacent buildings
thenumberofspecimensassociatedwithdecreasing were found (CJM 5980).
minimum temperatures is obvious. After a severe Dudweilerbei Saarbrücken(N:49°16' E:7°2',TK
frostlastingseveraldays(16-22Dec.)allspecimens 6708), Lidl shopping center, September 28,2007,
had disappeared. an aggregation of40 specimens was detected by
Steffen Potel (CJM 5981: Id, Aloysius Staudt
kg.).
Switzerland
KantonBasel-Landschaft,communityofLausen
(N:47°28'E:7°45'),about13kmsouthofBasel.In
September2007onthementionedwebsiteSabrina
specimens
S. noted an unusual aggregation (several dozens)
oflarge blackish harvestmen in a darkish stable.
We
could not obtain further information,but this
undoubtedlyconcernedLeiobunum sp.
Austria
Vorarlberg,communityofLauterachnearBregenz
dates
(N:47°30'E:9°44',TK8424):GüntherMuesburger
Fig.5:Leiobunumsp.,Isenburgpopulation,Essen,Germany. made notice of this opilionid on the mentioned
PopulationtrendfromSep.24toDec.31,2007.Bold line website and added a digital image of a group of
andsquares:numberofrecordedspecimens;loosely four 66 and ten 9 9 clumped in the corner ofa
dashed line:minimumtemperaturesrecorded inEssen
city;denselydashed line:regression lineofminimum white wall and ceiling.Two 66 and one 9 were
temperatures(Data kindlyprovidedbyKarolaWinzer). collected (CJM 6009).
Rheinland-Pfalz, Mayen (N: 50°19'50,8" E: Habitatandbehaviour
7°14T9,7" TK 5609), industrial area. A pair was Leiobunumsp.hasmainlybeenfoundinman-made
found resting at the side ofan isolated rock near environments, like buildings and industrial sites.
theroadingrassland.Atnightabout20specimens The two localities near Nijmegenwith the largest
were resting or walking on walls ofan old house, populations hitherto recorded were both situated
partlyovergrownbyivy(Hederahelix) (CJM 6003: in the direct vicinity ofan old disused brickstone
1066 3$ $ ALS leg. 1.10.2007.). factory. Avery strikingbehavioural feature ofthis
,
Enkenbach-Alsenborn, 15 km east of Kaisers- Leiobunumisitsstrongtendencytogrouptogether.
lautern(N:49°29'E:7°54',TK6513).InSeptember Large aggregations ofharvestmen were found on
2007 Heike Maurer sent two electronic images of walls, under roofgutters and window ledges and
Leiobunum spec,oneofthem showinganaggrega- also at the walls inside an old brickstone oven. It
tion of17 adult specimens at the northern roofed was observed that a negative phototaxis mustplay
part above the entrance of a residential building apartinthe choice ofthesedaytime shelters,most
(CJM 5988: 46619). ofwhich were protected from wind and direct
Saarland, Kleinblittersdorf-Auersmacher (N: sunlight. As a consequence the north-facingwalls
49°8' E: 7°2',TK6808),severalsmallaggregations ofbuildingswerepreferred.InGermanyitoccupied
ofabout 53 individuals in total were observed by similar habitats. Single individuals or smaller
Eva Bolz on the walls ofher house (CJM 5979: aggregationsofupto20individualswererestingon
266 3$ $ A. Staudtleg. 12.8.2007). thewallsofhousesaswellasshelteredplacesunder
Saarlouis (N,: 49T8' E: 6°44',TK 6606), mayors roofguttersandinshadedcornersofbuildings.Yet
office, citycenter, onAugust25 and September 1, Leiobunumsp.didnotseemtobeconfinedtoman-
34 H.Wijnhoven,AI.Schönhofer&J.Martens
madehabitats.ThelargecolonyinEssenlivedatthe individuallifetimemaybelimitedbythescarcityof
ruinedwalls ofan old castle within the Essen city (arthropod)foodsourcesinlateautumnandbythe
forest,whichisalargedeciduousforest,withonlya onsetoffrostinNovember/December.Thistypeof
single inhabited buildingin the neighbourhood. lifecycleiscommonamongEuropeanharvestmen,
Aggregations of Leiobunum sp. maintained including all Leiobunum species ofthe mentioned
their roosting places, once established, for longer region (MARTENS 1978).Numerousjuveniles ofa
periods of time, probably many weeks. At night Leiobunumspecieswerefoundunderstones,rubble
these predators swarm out on the walls to hunt and pieces ofwood on April 20. Later at this site
individually on other invertebrates, returning largegroupsofLeiobunumsp.wereobserved.Close
to their favoured daytime shelters during early toAmsterdamsomesubadultswerecollectedfrom
morning. In the Essen city forest the colony of the walls of a house earlyJune. So probably the
more than 500 individuals consisted of several firstjuvenile stages live at ground level, while the
sub-colonies, which more or less remained stable subadultsmaymovetothehigherstrataofwallsand
overaperiodofdays.Thenumberofindividualsand rocks.Thus,likeallLeiobunumspecies,thelifecycle
the exact locations ofthese aggregations changed ofsingle individuals is confined to oneyear.
onlyslightlyoverlonger intervals ofseveralweeks In total approximately about 6,240 adult
(K.Winzer,personalcomm.).ObservationsinThe Leiobunum sp. were recorded inThe Netherlands.
Netherlandsindicatedthesefavouredshelterswere One large group of 770 specimens was counted
used year after year by the successive generations. with the help ofdigital images. Also a few other
The stability ofthese local aggregations and their groupswere countedin this manner.Basedonthis
long-term use could simply be demonstrated by experienceformostotheraggregationsthenumbers
the presence of faeces which were deposited on could be estimated. Aggregations observed on
thewall. Severalimagesplacedonweb sitesclearly exactly the same spot were recorded only once.
pointed outthe daytime shelters as concentrations The sex ratio for 8<5is 46.6 % (n=653: 304 88
,
of numerous small black droppings. On white 349 $ $).
painted walls ofhouses these droppings could be
quite annoyingto the residents. On two occasions Accompanyingharvestmanspecies
the inhabitants stated for this reason they had Time and again it was observed that in The
removed and destroyed all harvestmen from their Netherlands on walls with large aggregations of
housewalls (HW). Leiobunum sp. almostno otherharvestman species
AggregationsofLeiobunum sp.wereveryeasily were to be found. This Leiobunum seemed to
disturbed, especially by sudden changes in light absolutely dominate these habitats. On some rare
conditions.If,forexample,onemovedtoocloseby, occasionssingleindividualsofLeiobunumrotundum
the animals suddenlystarted to move theirbodies (Latreille, 1798), Leiobunum blackwalli Meade,
upanddowninafastrhythmicmotion.Thisabrupt 1861,Dicranopalpusramosus(Simon, 1909), Opilio
‘bobbing’ behaviourwould swiftly spread through canestrinii (Thorell, 1876), Opilioparietinus (De
awholegroup,withindividuals movingawayfrom Geer, 1778) andPhalangiumopilioLinnaeus, 1758
the disturbance. Eventuallythegroupwouldbreak were observed at the margins ofsuch Leiobunum
up. aggregations.MostfrequentlyLeiobunumrotundum
alsowasfoundinsidethesegroups.Furthermorein
Phenology the surrounding areas remarkablyfewharvestmen
Untilnowwe have no detailedinformation on the wererecorded.Especiallyverycommonspecieslike
life cycle ofLeiobunum sp. In Europe it is mature Paroligolophus agrestis (Meade, 1855) and Oligolo-
in summer and autumn. Most records of single phus tridens (C.L. Koch, 1836) which, at least at
individuals and mass aggregations only consisted night, penetrate the herb and bush strata seemed
of adult specimens. They dated from the begin- almost completelyabsent.
ningofAugusttotheendofDecember.Maximum
numbers were observed in September. In October Predators
the aggregations started to desintegrate. Egg Afewobservationsweremadeofotherinvertebrates
deposition apparentlyoccurs duringthattimespan preying on Leiobunum sp. Frequently spider webs
and eggs probably overwinter. The end of the of Nuctenea umbratica (Clerck, 1757), Araneus
UnknownLeiobunumspeciesinvadingEurope 35
diadematus Clerck, 1757 and species ofthe family none tendsto aggregatetocomparable numbersof
Agelenidae contained bodies and/or seperate legs individuals (Tsurusaki,personal comm.).
A
ofthisopilionid. salticidspiderMarpissamuscosa Observations on overwintering mass aggre-
(Clerck, 1757)was observed on awallwith abody gationsofLeiobunumpaessleriRoewer,1910incaves
ofthis Leiobunum in itsjaws, with the legs being in British Columbia suggested that the combined
removed. action ofmany opilionids’ scent glands was more
effective as a repellant against predators than one
Discussion individual’s effort (HOLMBERG et al. 1984). In
Behaviour this respect the formation ofaggregations maybe
A prime feature ofLeiobunum sp., otherwise only regardedadefensive strategy.Also,inouropinion,
rarely observed in European Opiliones, is its the white tibia tips ofLeiobunum sp. could have
tendencytoaggregateintomassivenumbers.Their a defensive function. These white tips were most
daytime shelters may contain over one thousand distinct on the longest legs II and IV (Figs, la-
individuals.InEurope,similarbehaviourisknown b). In aggregations slight movements ofthe legs
from Amilenus aurantiacus (Simon, 1881), a long mayprovide for a ‘floating’ sheet of‘light flashes’,
legged species not closely related to Leiobunum, distracting the attention ofpredators (like birds)
when the subadults wander into cave systems, awayfrom thelowerlayerofvulnerable bodies. So
where they moult to adulthood and stay there in perhaps allLeiobunumspecieswithwhite tibiatips
groups ofhundreds and even thousands over the will have the tendency towards forming groups.
winter (MARTENS 1978). Sightings of groups More hypotheses as towhyharvestmen aggregate
ofL. rotundum, numbering a few dozens up to a arepresentedbyMACHADO&MAC1AS-0RD0NEZ
hundred individuals, have been observed in The (2007).Accordingto alistinthiscontributionitis
Netherlands (HW personal obs.). In general, obviousthatthesizeofLeiobunumsp.aggregations
European Leiobunum species never aggregate ranks among the seven or eight species with the
to numbers presently observed for Leiobunum largest aggregations everobserved in Opiliones.
sp. HOLMBERG et al. (1984) classified such
aggregations into two types: ‘loose’ and ‘dense’. In Habitat
looseaggregationsthebodiesoftheopilionidswere Untilnowin EuropeLeiobunum sp.is more orless
orientedindifferentdirectionswiththelegsflexed confined to human environments, mainlywalls of
oroutstretchedontheground.Theanimals’bodies houses.Howeverthelargecolonyofmorethan500
could stillbe distinguished separately, although in individuals living at the ruinedwalls ofa castle in
most cases the opilionids’bodies were oriented in theEssencityforestindicatesLeiobunumsp.prima-
thesamedirection,withtheir‘heads’down.Indense rily maybe regarded a rock-dwelling species.The
aggregationstheopilionidsclungtogethersotightly, preference for sheltered rocky habitats coincides
the individual animals were barely recognizable. with several Dutch records ofLeiobunum sp. at
These aggregations may consist of several layers isolated places far away from buildings, e.g. piles
of opilionids. They attached themselves to the ofconcrete rubble at the banks ofthe riverWaal.
substrateandtothoseopilionidsunderneathbythe
clawsoftheirpedipalpsorchelicerae.Thelegswere Invasionstrategies andinfluenceonindigenous
hanging straight down motionless, which would species
look like “a mass ofblack horsehair” (HlLLYARD The European harvestman fauna always has
1999 citing an observation of uncertain species been subject to considerable changes in species
affiliation in Great Britain mentioned byWOOD composition.Someoftherecentchangeshavebeen
1863: 677). This type of dense aggregation was documentedin detail,showingthatseveralspecies
occasionallyobserved inLeiobunum sp.within the adapttonewterritorieswithoutnotablyinfluencing
largergroups ofatleast 140 animals. However, all the indigenous opilionid fauna. OfOpilio ruzickai
sorts of intermediate types of aggregations were Silhavy, 1938,originatingfrom the Balkanregion,
oftenseen,withharvestmendenselypackedin the ononeoccasiononlytwo specimenswerefoundin
centreoftheaggregationandthe‘loosetype’atthe Innsbruck, Austria (CJM 3521, Id 9, Innsbruck,
peripheryofsuch clusters. In other regions rich in Stadtgebiet, Weiherburggasse, an Hauswänden,
Leiobunumspecies,likeJapan(SUZUKI1953,1976), 730-800m,JMleg.27.9.-1.10.1986).IntheVienna
36 H.Wijnhoven,AI.Schönhofer&J.Martens
region, Austria, a population of this species has itself, probably originating from the Carpathians
&
persisted for at least 45 years. Once established, it (Martens Schönhofer in preparation).
enlargedits territoryforseveraldecades (GRUBER With the advance ofOpilio canestrinii,Leiobunum
&
1996, KOMPOSCH Gruber2004) butwithin a tisciaemoreorlesscompletelydisappearedfromthe
coupleofyearsremainedmoreorlessstableinrange western countries ofits area (TOFT2004,personal
and numbers anddid notmuchinfluence thelocal comm.).
species set (GRUBER 1996). Theseinvasiveharvestmenallhaveincommon
Other recent invasions, like the one of that they are long-legged species, colonizing man
Dicranopalpusramosus originatingfromthewestern made environments. Also some of these species,
,
Mediterranean region, turned out to be more after having been naturalized, succeeded in
influential. In the beginning it expanded its range colonizing more or less natural habitats, like
only slowly to southern Spain and further on to forests. In Germany, O. canestrinii is presently
&
GreatBritain(RAMBLA1986,SANKEY SAVORY found in broad-leaved forest habitats, e.g., in the
1974), but since around 1990 it has been rapidly TaunusMountainsintheFrankfurtamMainarea.
moving northeast (NOORDIJK et al. 2007). The Itwasrecordedinhighnumbersontreetrunkswith
species reached Germany (SCHMIDT 2004), but smooth bark (e.g., Acer) in the Oder inundation
until now the populations are patchily distributed forests (Brandenburg; Lossow, near Frankfurt a.d.
and locally only small numbers ofindividuals are Oder, CJM 4779, ALS leg. 16.10.2005). Opilio
concerned.Inthe Netherlands andparts ofFrance canestrinii is now the dominant long-legged
it is locally quite common nowadays not only on species there. In this habitat Leiobunum rotundum
walls of houses in urban habitats. It has already undL.blackwalli formerlythepredominantspecies
,
adaptedtonaturalhabitatsaswell.Althoughitwas in the herb layer and on tree bark are nowadays
suggested it maycompetewith indigenous species represented only by a minor fraction ofthe total
likeLeiobunumrotundumandParoligolophusagrestis population oflong legged harvestmen in summer
(WIJNHOVEN 2006) ALS found both species andautumn.IntheNetherlands,too, O. canestrinii
syntopicallywith D. ramosus in France (Bretagne, is nowone ofthe most abundant species in awide
Dep. Morbihan, West ofLorient, Guidel-Plages, range ofhabitats.
Le Pointic, in September 2005). The population The invasion of Leiobunum sp. into Europe
density of the indigenous species did not seem may, however, exceed our experience with alien
to be influenced markedly. Paroligolophus agrestis harvestmen. This newly-arrived, long-legged
was numerous and Leiobunum rotundum occurred species is capable ofrapidly spreading into man-
regularly. Wall-dwelling specimens ofD. ramosus madehabitats.Itobviouslyhasahighreproduction
were found side by side with Phalangium opilio in rate, resulting in large populations within a few
nearbysettlements.Itappears thatthis specieswill years.If,as some observations alreadysuggest,this
rathersupplementtheEuropeanspeciescommunity species will be able to adapt to central European
ofharvestmen than disturb it. climatic conditions and invade natural habitats as
Otherfaunalchangesweremuchmoredramatic. well, its offensive character could become a real
The large-scale invasion of Opilio canestrinii threat. Many endemic species including those of
,
probably from trans-alpine Italy, starting around the Alpine region couldbe atrisk.
1970considerablyinfluencedthecentralEuropean Largenumbersofopilionidsneedlargeamounts
fauna.Withinafewdecades O. canestriniiinvaded offood. Among other arthropods, many syntopic
all of central Europe and beyond and became (andsynanthropic)harvestmenspeciesmaybepart
an ubiquitous species. During this process wall- oftheirmenu,especiallyjuveniles.SinceLeiobunum
dwellingspecieslikeLeiobunumrotundumandOpilio sp.seemstoreachmaturityquiteearly(endofJuly,
parietinus became rare or disappeared completely, beginning ofAugust) this may act as a powerful
especially the latter species. The same happened competitive weapon. Not to mention the direct
with Leiobunum tisciae Avram, 1971 which is (or effects of disturbing other opilionids, simply by
at least was until recently) widely distributed in theirlarge numbers.
northern Germany around the Baltic coast and We conclude that Leiobunum sp. has been
southernScandinavia(MARTENS 1978,ENGHOFF introduced into Europe around the year 2000,
1988, TOFT 2004). It is an immigrant species the country of introduction probably being the
