2002. The Journal of Arachnology 30:455±460

LINYPHIA TRIANGULARIS, A PALEARCTIC (ARANEAE, ) NEW TO

Daniel T. Jennings1: USDA, Forest Service, Northeastern Research Station, 686 Government Road, Bradley, Maine 04411 USA Kefyn M. Catley: Rutgers, The State University of New Jersey, 10 Seminary Place, New Brunswick, New Jersey 08901-1183 USA

Frank Graham, Jr.2: National Audubon Society, 700 Broadway, New York, NewYork 10003 USA

ABSTRACT. A Palearctic spider, Linyphia triangularis (Clerck 1757), has been accidentally introduced to the U.S.A. and populations successfully established in Maine. The date, origin, and focal point(s) of introduction are unknown, but suspected to be recent, European, and maritime. Extensive historical col- lections, records of maritime commerce, and recent chronological collections support this hypothesis. Results of cursory surveys in 1999 and 2000 indicate that L. triangularis is now widely distributed in Maine with specimens taken in 15 of 16 counties. The potential impact(s) of L. triangularis on the native araneofauna are unknown, but possibly detrimental. In , this exhibits aggressive behaviors (e.g., web ``take-overs'') toward conspeci®cs and congenerics. Keywords: Introduced species, Maine , aggressive linyphiid, recent invasions

Spiders are dispersed over great distances triangularis (Clerck 1757), which presumably by aerial ballooning and by human transport is an immigrant from Europe. (Gertsch 1979; Kaston 1983). Several species Chronology of discovery.ÐDuring 1991, have been implicated as immigrants to North 1996, and 1997, F. G., Jr. collected female lin- America from Europe and elsewhere; com- yphiid spiders in old ®eld vegetation at Mil- mon examples include Araneus diadematus bridge, Washington County, Maine. Subse- Clerck 1757, Salticus scenicus (Clerck 1757), quently, D. T. J. determined the specimens to Pholcus phalangioides (Fuesslin 1775), be Linyphia triangularis (Clerck 1757), a Pa- Achaearanea tepidariorum (C.L. Koch 1841), learctic spider. Peter J. van Helsdingen of the Tegenaria domestica (Clerck 1757), and Dys- National Museum of Natural History in Lei- dera crocota C.L. Koch 1838 (Gertsch 1979). den con®rmed the species identity. More recently, the northeastern United States The abundance of Linyphia triangularis in and have seen introductions of Stea- Maine became evident when 9 males, 20 fe- toda bipunctata (Linnaeus 1758) from Europe males, and 2 juveniles were readily taken on (Nyffeler et al. 1986), and of Achaearanea ta- 19 August 1998 at Schoodic Peninsula, Aca- bulata Levi 1980, possibly from Asia (Don- dia National Park, Winter Harbor, Hancock dale et al. 1994). In California, Griswold & County. Our suspicion that Linyphia triangu- Ubick (2001) noted the introduction of Zorop- laris had successfully established a breeding sis spinimana (Dufour 1820), a native to the population at Schoodic Peninsula was con- Mediterranean region. Here we describe the ®rmed on 19 August 1999, when 5 males and invasion and establishment of yet another ex- 18 females were taken in Ͻ 2 h at the same otic spider in North America, i.e., Linyphia site sampled in 1998. Most were found in slightly dome-shaped webs on understory 1 Current address: P. O. Box 130, Garland, Maine forbs (Solidago sp.), grasses, ferns, and shrubs 04939-0130 USA. near the ground; a few were taken by beating 2 Current address: Box 170, Wyman Road, Milbrid- and sweeping lower-crown foliage of red ge, Maine 04658 USA. spruce, Picea rubens Sargent, and by search-

455 456 THE JOURNAL OF ARACHNOLOGY ing loose bark and tree boles of paper birch, of Androscoggin, Franklin, Kennebec, Knox, Betula papyrifera Marshall. Lincoln, Oxford, Penobscot, Piscataquis, Sa- Males and females were observed cohabi- gadahoc, Somerset, and Waldo (Map 1); none tating in the same web; however, mating and were found in Aroostook County. Additional oviposition were not observed either year. searches during August±September, 2000, Associated species of sheet-line weavers failed to yield specimens of this exotic spider (Linyphiinae) at Schoodic included: adults of in mid, northern, and far ``downeast'' Maine Bathyphantes pallidus (Banks 1892), Cen- (Map 1). Of Maine's 16 counties, only Aroos- tromerus denticulatus (Emerton 1909), Dra- took County remains to yield specimens of L. petisca alteranda Chamberlin 1909, Helopho- triangularis. The chronological and geograph- ra insignis (Blackwall 1841), Lepthyphantes ic distributions of our records suggest that the calcaratus (Emerton 1909), L. turbatrix (O.P.- species might be moving inland from a coastal Cambridge 1877), viaria (Black- locus or loci. Thus far, L. triangularis has not wall 1841), radiata (Walckenaer been found in Quebec (Paquin et al. 2001) or 1841), and Tapinopa bilineata Banks 1893; in New Brunswick (Buckle et al. 2001). and juveniles of , Helophora, Ner- Introductory date, origin, & mode.ÐThe iene, and Pityohyphantes. Based on collection actual date of arrival, source or origin of em- frequency, none of the associated adult liny- igration, and mode of travel are unknown. phiids (n ϭ 18) was as common as Linyphia Historical collections of spiders in New Eng- triangularis in 1998; none of associated adult land provide some evidence that Linyphia tri- or juvenile linyphiids (n ϭ 19) was as com- angularis arrived recently (i.e., within the last mon as L. triangularis in 1999. half-century) in Maine. In the late 1800's and Prior collections.ÐNone of the contacted early 1900's, James H. Emerton and Elizabeth museums or institutions had records of L. tri- B. Bryant collected spiders in Maine and other angularis collected in Maine or elsewhere in New England states, but none of their pub- North America. These included: The Ameri- lished lists (see Bonnet 1945) include L. tri- can Museum of Natural History (AMNH), angularis. During the last half-century, spi- New York; California Academy of Sciences ders have been collected extensively in New (CAS), San Francisco; Canadian National England and the Maritime Provinces; e.g., Collection (CNC), Ottawa; Field Museum of Charles D. Dondale, James H. Redner, and as- Natrural History (FMNH), Chicago; Harvard sociates in Ontario, Quebec, New Brunswick, Museum of Natural History (HMNH), Cam- and Newfoundland; Robert L. Edwards in bridge; Thomas Burke Museum (TBM), Se- Cape Cod, Massachusetts; Benjamin J. Kaston attle; and, U. S. National Museum of Natural in Connecticut; and Herbert W. Levi in Mas- History (NMNH), Washington. sachusetts, New Hampshire, Maine and other Procter (1946) listed 15 families, 94 genera, New England states. None of these collections and 179 species of spiders collected from var- yielded specimens of L. triangularis. ious habitats on Mount Desert Island, Han- Prior to the discoveries in Maine, the cock County, Maine. Linyphia triangularis known geographic distribution of L. triangu- was not among them. laris included the Palearctic region from Examination of D. T. J.'s undetermined ma- southern, western, and northern Europe to Si- terial yielded 7 males and 10 females of L. beria and in the east (Helsdingen 1969). triangularis collected during August of 1983, The species is very common in the British 1986, 1989, and 1994, and from the counties Isles (Locket & Millidge 1953) and in Scan- of Cumberland, Hancock, Penobscot, and dinavia (Nielsen & Toft 1990). With the recent York (Map 1). The earliest record of L. tri- expansion of worldwide commerce, any one angularis in Maine is a female taken 28 Au- or more countries in the Palearctic region gust 1983 at Stover Corner, Brooksville, Han- could serve as the origin(s) of emigration of cock County, Maine. L. triangularis to North America. Survey results.ÐDuring August±Septem- Description, webs, and life history.ÐDe- ber, 1999, 15±20 minute searches were made scriptions and illustrations of Linyphia trian- at numerous localities and among diverse hab- gularis are provided by Helsdingen (1969) itats in rural Maine. The survey yielded 64 and Roberts (1993, 1995), and include illus- specimens of L. triangularis from the counties trations of the male and female genitalia. The JENNINGS ET AL.ÐINTRODUCED LINYPHIID 457

Map 1.ÐDistribution of collection and survey sites in Maine for the Palearctic sheet-line weaver, Linyphia triangularis (Clerck, 1757). Closed circles, L. triangularis present, all data inclusive (1983± 2000); open circles, L. triangularis not present in 1999 or 2000. 458 THE JOURNAL OF ARACHNOLOGY

Figures 1±4.ÐDorsum of carapace and abdomen. 1, 2. Linyphia triangularis collected in Maine. 1. Male; 2. Female; 3, 4. Pityohyphantes sp. collected in Maine. 3. Male; 4. Female. Scale bars ϭ 1 mm. (Drawings by N. Sferra). color pattern of L. triangularis closely resem- Bristowe (1958), Jones (1983), and Preston- bles that of the North American Pityohyphan- Mafham (1984). It consists chie¯y of a ¯at- tes costatus (Hentz 1850); dorsally, both spe- tened sheet, slightly arched in the center, and cies have a bifurcated, ``tuning-fork'' marking held in place by scaffolding threads above and on the carapace, and a herring bone pattern on below the sheet. The web lacks a retreat, with the abdomen (Figs. 1±4). The latter is less ev- the resident spider hanging upside-down near ident in L. triangularis males (Fig. 1). The the center of the sheet. The webs of L. tri- markings of L. triangularis also resemble angularis in Maine more closely resemble the those of P. phrygianus (C. L. Koch 1836), an- webs of Pityohyphantes species than those of other European immigrant in Maine, but less Neriene radiata (cf. Roberts 1995, p. 74). common than P. costatus. Ventrally, the fem- The species is univoltine in Europe, over ora of L. triangularis are devoid of dark spots, wintering as eggs in leaf-litter beneath trees while black or dark-brown spots are usually and shrubs (Turnbull 1960). Juvenile spider- present on the femora of P. costatus and P. lings emerge from the egg sac in the spring phrygianus (cf. Roberts 1993, Part 2, plates (May), and reach maturity by late July or Au- 231 & 233). Unlike Pityohyphantes, the tun- gust (Toft 1978, 1989). Development is pro- ing-fork markings do not extend to the pos- tandrous, with males reaching adulthood terior eye rows in L. triangularis (Figs. 1±2). about a week earlier than females. The sexu- The web of L. triangularis has been de- ally mature males enter the webs of subadult scribed and illustrated by Nielsen (1931), females, where they remain until the female JENNINGS ET AL.ÐINTRODUCED LINYPHIID 459 reaches maturity (Toft 1989; Nielsen & Toft its natural enemies of origin, populations in 1990). Shortly afterwards, mating takes place Maine are apt to expand rapidly unless tem- in the web (Herberstein 1997; Stumpf 1990), pered by native parasites, predators, and path- followed by oviposition in October or Novem- ogens. ber (Nielsen & Toft 1990). The life history of We conclude that L. triangularis has suc- L. triangularis in North America remains to cessfully invaded and established breeding be studied. populations in Maine. The future of these pop- Potential impacts.ÐWhat are the potential ulations and their potential impacts on impacts of L. triangularis on the native spider Maine's diverse insect and spider faunas war- and insect faunas in Maine? Such impacts rant further investigation. could be bene®cial, neutral, or detrimental. In northern Europe, L. triangularis usurps the ACKNOWLEDGMENTS webs of conspeci®cs and congenerics (Toft We gratefully acknowledge the enthusiastic 1987, 1990). Though native Linyphia species cooperative assistance of our former students are absent in eastern North America (Helsdin- at the Humboldt Field Research Institute in gen 1969; Buckle et al. 2001), L. triangularis Steuben, Maine. Without their generous help, could invade the webs of associated species this paper would not exist. David Manski, such as Frontinella communis, Pityohyphantes Acadia National Park, provided collecting costatus,orNeriene radiata. If so, will this permits; Daniel H. Kusnierz, Penobscot Indian alien spider compete with native species for Nation, plotted the distribution data for Map microhabitat space and food, or are such re- 1; Nancy J. Sferra, The Nature Conservancy, sources suf®ciently abundant to provide niche made the drawings for Figs. 1±4; and Joyce partitioning and species coexistence? Perhaps E. Longcore gave technical assistance. Special differences in developmental phenologies or thanks are due: Peter J. van Helsdingen for other ecological-behavioral parameters will con®rmation of species identity; Sùren Toft, minimize impacts between invader and native University of Aarhus, for reprints of pertinent species. literature; and colleagues for their responses We suspect that biodiversity will be affect- to inquiries about records of L. triangularis in ed by this introduction. Collectively, invasion North American collections. by exotics is the second most prevalent cause Donald J. Buckle, Peter J. van Helsdingen, of species endangerment after habitat loss Gustavo Hormiga, and one anonymous re- (Wilson 1992; Czech et al. 2000). For exam- viewer provided constructive comments on ple, in some regions of northeastern North earlier drafts; we thank each for their time and America, the native Steatoda borealis (Hentz efforts. 1850) has been displaced by the European S. LITERATURE CITED bipunctata (Linnaeus 1758) (Nyffeler et al. 1986). Will native sheet-line weavers and oth- Bonnet, P. 1945. Bibliographia Araneorum. Tome er spiders be displaced by L. triangularis? 1. Reprinted without change, 1968. Noble Offset These and other questions pose unique chal- Printers, Inc., U.S.A. Bristowe, W.S. 1958. The World of Spiders. Col- lenges to researchers and resource managers lins, London. alike. See Cox (1999 & lit. cited) for a review Buckle, D.J., D. Carroll, R.L. Crawford & V.D. of potential impacts of invasive exotics. Roth. 2001. Linyphiinae and Pimoidae of Amer- Linyphia triangularis meets 7 of the 8 cri- ica north of Mexico: Checklist, synonymy, and teria that characterize a successful invader literature. Pp. 90±191. In Contributions aÁ la con- (Ehrlich 1986), i.e., 1) abundant in original naissance des AraigneÂes (Araneae) d'AmeÂrique range; 2) polyphagous instead of monopha- du Nord. (P. Paquin & D.J. Buckle, eds.). Fa- gous or oligophagous; 3) short generation breries, SuppleÂment 10. time; 4) fertilized female able to colonize Cox, G.W. 1999. Alien Species in North America alone; 5) larger than most relatives; 6) asso- and Hawaii: Impacts on Natural Ecosystems. Is- land Press, Washington, District of Columbia. ciated with Homo sapiens; and 7) able to Czech, B., P.R. Krausman & P.K. Devers. 2000. function in a wide range of physical condi- Economic associations among causes of species tions. Only its genetic variability, compared to endangerment in the United States. BioScience that of non-invaders, remains to be ascer- 50:593±601. tained. Because this alien species is free from Dondale, C.D., J.H. Redner & L. LeSage. 1994. A 460 THE JOURNAL OF ARACHNOLOGY

comb-footed spider, Achaearanea tabulata, new Theridiidae). Canadian Journal of Zoology 64: to the fauna of Canada (Araneae: Theridiidae). 867±874. Journal of Arachnology 22:176±178. Preston-Mafham, R. & K. Preston-Mafham. 1984. Ehrlich, P.R. 1986. Which will invade? Pp. Spiders of the World. Facts on File, Inc. N.Y. 79±95. In Ecology of Biological Invasions of Procter, W. 1946. Biological Survey of the Mount North America and Hawaii. (H.A. Mooney & Desert Region Incorporated. Part VII. The Insect J.A. Drake, eds.). Springer-Verlag, New York. Fauna. The Wistar Institute of Anatomy and Bi- Gertsch, W.J. 1979. American Spiders. 2nd ed. Van ology, Philadelphia, Pennsylvania. Nostrand Reinhold, New York. Roberts, M.J. 1993. The Spiders of Great Britian Griswold, C.E. & D. Ubick. 2001. Zoropsidae: A and Ireland. Compact ed. Vols. 1, 2, & 3. Harley spider family newly introduced to the USA (Ar- Books, Colchester, Essex. aneae, Entelegynae, Lycosoidea). Journal of Ar- Roberts, M.J. 1995. Collins Field Guide: Spiders of achnology 29:111±113. Britian & Northern Europe. Harper Collins, Lon- Helsdingen, P.J. van. 1969. A reclassi®cation of the don. species of Linyphia Latreille based on the func- Stumpf, H. 1990. Observations on the copulation tioning of the genitalia (Araneida, Linyphiidae), behaviour of the sheet-web spiders Linyphia hor- Part I. Linyphia Latreille and Neirene Blackwall. tensis Sundevall and Linyphia triangularis Zoologische Verhandelingen, No. 105. E.J. Brill, (Clerck) (Araneae: Linyphiidea). Bulletin of the Leiden, The . Society of European Arachnology. 1:340±345. Herberstein, M.E. 1997. Niche partitioning in three Toft, S. 1978. Phenology of some Danish beech- sympatric web-building spiders (Araneae: Liny- wood spiders. Natura Jutlandica 20:285±301. phiidae). Bulletin of the British Arachnological Toft, S. 1987. Microhabitat identity of two species Society 10:233±238. of sheet-web spiders: ®eld experimental demon- Kaston, B.J. 1983. Synanthropic spiders. Pp. 221± stration. Oecologia (Berlin) 72:216±220. 245. In Urban Entomology: Interdisciplinary Toft, S. 1989. Mate guarding in two Linyphia spe- Perspectives. (G.W. Frankie & C.S. Koehler, cies (Araneae: Linyphiidae). Bulletin of the Brit- eds.). Praeger, New York. ish Arachnological Society 8:33±37. Locket, G.H. & A.F. Millidge. 1953. British Spi- Toft, S. 1990. Interactions among two coexisting ders. Vol. II. The Ray Society, London. Linyphia spiders. Acta Zoologica Fennica 190: Nielsen, E. 1931. The Biology of Spiders. Vol. I. 367±372. Copenhagen. Turnbull, A.L. 1960. The prey of the spider Liny- Nielsen, N. & S. Toft. 1990. Alternative male mat- phia triangularis (Clerck) (Araneae, Linyphi- ing strategies in Linyphia triangularis (Araneae, idae). Canadian Journal of Zoology 38:859±873. Linyphiidae). Acta Zoologica Fennica 190:293± Wilson, E.O. 1992. The Diversity of Life. The 297. Belknap Press of Harvard University Press, Nyffeler, M., C.D. Dondale, & J.H. Redner. 1986. Cambridge, Massachusetts. Evidence for displacement of a North American spider, Steatoda borealis (Hentz), by the Euro- Manuscript received 1 June 2001, revised 27 No- pean species S. bipunctata (Linnaeus) (Araneae: vember 2001.