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Italians have made many importantcontributions to the culture andaccomplishments of the UnitedStates, and some of these are not gen-erally appreciated. Two of the moreunderappreciated contributions are

the Italian wall lizards, Podarcis siculaand Podarcis muralis. In the 1960s and1970s, Italian wall lizards were importedto the United States in large numbers forthe pet trade. These hardy, colorful littlelizards are common in their home coun-try, and are easily captured in large num-bers. Enterprising animal dealers boughtthem at a cut rate in Italy and sold themto pet dealers all over the United States.Not all of these lizards made it to hometerrariums, however — in at least fourcities in North America, lizards escapedand survived in suburban neighbor-hoods. One of these populations beganin Garden City, just a few miles west ofHofstra University. This population hasspread in all directions, and recently theItalian lizards have been seen on theHofstra campus.

The scientific community’s view ofthe release (deliberate or accidental) ofanimals and plants into new places haschanged over the years. In the past,amateur and professional scientists oftenactively promoted the introduction offoreign species into new habitats. Forexample, professional wildlife biologists

brought ringneck pheasants (Phasianuscolchicus) to North America for sporthunting, and pheasants have survived sowell (for example, on Hofstra’s NorthCampus) that many people are unawarethat the species originated in China. Ofcourse most of our common agriculturalspecies — except for corn, pumpkins,and some beans — are non-native. The

two most common bird species in theUnited States — starlings (Sturnus vul-garis) and English sparrows (Passerdomesticus) — were both introducedhere from Europe. Starlings got theirbeginning in Central Park in 1890,when someone decided that New Yorkshould be home to all the bird species

mentioned by Shakespeare. Also in thelate 1800s naturalists introduced thesmall Indian mongoose (Herpestes javan-icus) to the islands of Mauritius, Fiji,Hawai’i, and much of the West Indies,supposedly to control the rat popula-tion. Rats were crop pests, and in mostcases the rats were introduced fromEurope. Instead of eating lots of rats, themongooses ate numerous native ani-mals, endangering many species andcausing plenty of extinctions. They alsobecame carriers of rabies. There aremany more cases of introductions likethese, and at the time the scientificcommunity has either supported orignored them.

In more recent years, as the list ofintroductions with disastrous results hasgrown, many scientists have vigorouslyopposed further species introductions.Invasive species are now recognized asone of the most important causes ofnative species endangerment and extinc-tion, and a considerable portion of con-servation resources worldwide aredevoted to combating the spread ofinvasive species. Invasive species hit usin the wallets as well. For example,zebra mussels (Dreissena polymorpha), aspecies originally from Europe, werecarried to the Great Lakes in the ballastwater of large ships. They have spreadrapidly throughout lakes of the Midwest

“Italian Immigrants”Flourishon Long IslandRussell BurkeAssociate ProfessorDepartment of Biology

Annual Patterns

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Number of Podarcis sicula observed in surveys by month. Italian datafrom Foà et al. (1992b); New York data from Burke and Ner (2005).Triangles represent average number of lizards at Italian site in 1988(Foà et al., 1992b); circles and squares represent average number oflizards at New York site in 1999 and 2000, respectively.

HOFSTRAHORIZONS15

and eastern United States, now causingbillions of dollars of damage annually tofactory and power plant water intakesystems. Australian melaleuca(Melaleuca quinquenervia) trees werebrought to southern Florida in the early1900s to help dry up swamps, but havespread out of control, forming thickforests that exclude all native trees.Melaleuca forests are so successful atabsorbing ground water that they alterlocal water flow patterns and regionalclimate. Because melaleuca bark ishighly flammable yet the trunk is fireresistant, lightning fires in melaleucaforests quickly become extremely hotcrown fires that spread into naturalforests, clearing them of all vegetationand preparing them for further invasionby the surviving melaleucas. Gypsymoths (Porthetria dispar), originallybrought to the United States for silkproduction, failed entirely in thatregard, but escaped from laboratories in1868. Since then they have become oneof the most devastating forest pests inour country, stripping the leaves of treesacross millions of acres in the northeastand heading south through theAppalachian Mountains. As a result ofthese three species and many others,U.S. taxpayers now spend $100-200 bil-lion annually to monitor, contain, andcontrol invasive species. Scientiststoday pay close attention to the spreadof species, and work hard to limit fur-ther introductions. Invasive speciesecology is perhaps the most rapidlygrowing subfield of ecology.

Against this backdrop of introduc-tions causing ecological disaster, wheredo the scaly little Italian immigrants fitin? I am frequently asked whether theItalian wall lizards have a negative effecton their new environment, like so manyother invasive species have. I’m askedthis by gardeners who have them intheir gardens, homeowners who havethem in their basements, amateur her-petologists who want them in theirbackyards, and biologists who studyinvasive species generally. And anothercommon question is, How do they sur-vive the cold Long Island winters?

My students and I have been work-ing on the answers to all of these ques-

tions. We know Italian wall lizards aredoing very well on Long Island becausethere are many places where they arevery abundant, and there must be thou-sands scattered throughout Long Island.This all started when a small number oflizards were released from a pet shopjust off Hempstead Turnpike in GardenCity in 1966. Six years later, accordingto a Cornell University undergraduatestudent doing a research project here,

juvenile lizards were abundant, and thepopulation was expanding. They hadspread out in a semicircular pattern toabout 1/4 mile from the original releasesite. Ten years later they had spreadover 0.6 mile around the release site,and by the early 1990s they were seenas much as 11/2 miles from the originalrelease site. Now they exist in somelarge, more or less continuous popula-tions spread throughout entire neigh-borhoods in Nassau County, and a num-ber of small isolated populations as farwest as The New York Botanical Gardenin the Bronx and as far east as HamptonBays on the beach. They are stillspreading, mostly through three meth-ods. First, they disperse on their own,primarily along power lines and railroadright-of-ways. They make good use of

Long Island Rail Road property as a safecorridor, and spread into neighborhoodsthat border the tracks. Second, there arepeople who deliberately release lizardsin new places. That’s almost certainlyhow lizards got to Leeds Pond Preserveon the north shore, The New YorkBotanical Garden, and Planting FieldsArboretum in Oyster Bay. Finally,lizards are moved accidentally by peo-ple. For example, people moving mulchfrom areas where lizards are commonare probably also moving lizard eggs.

Why have they done so well inNorth America? Both species of walllizards have lived in urban and subur-ban parts of Italy for thousands of years,and they really don’t live in any habitatsin Italy that could be called natural any-more. They have adapted to living nearhumans; in fact, one of the placesthey’re most common here is a nurseryschool where people (especially chil-dren) pass right in front of them all day.The lizards carry on with their lives,hunting and socializing, undisturbedunless people get too close. Here onLong Island, they have spread throughneighborhoods where they can findshelter in which to hide, but near openspaces where they can hunt for food. Sofar they have colonized suburban areas,gardens and parks here — they don’teven seem to like more natural habitatson Long Island.

Two other reasons the lizards arespreading quickly and building up largepopulations in their new country arethat they have no significant competi-tors or predators here. There are noother lizard species on Long Island —none of the native species that exist innearby New Jersey made it here, and noother lizard species have been intro-duced. And perhaps because there areno other lizards here, there are really nopredators that specialize on lizards. InItaly, lizards are commonly eaten by avariety of snakes and birds. On LongIsland, we have one snake species thatmight occasionally eat lizards (milksnakes, Lampropeltis triangulum), but sofar there is little overlap in the ranges ofmilk snakes and wall lizards. I’ve seensome of our common birds looking atlizards, but there’s no evidence that

Photo by Bill Davis. ©2003 Newsday, Inc. Reprinted with permission.

16 HOFSTRAHORIZONS

birds eat lizards here. The one predatorof any consequence here is cats, whichalso eat wall lizards in Italy. One LongIsland homeowner showed me her prizelizard catcher — and a collection oflizard tails. The cat was not always fastenough to get entire lizards, but man-aged to get the tails of its escaping prey.These lizards quickly drop their tailswhen that will help them get away, andthe tails wiggle and squirm enticinglyafter detachment from the rest of thelizard. Those lizards can go on to leadlong, healthy lives and regrow theirtails.

Do the introduced lizards have anegative effect on local species?Although I get many calls each springand summer from frightened suburban-ites with lizards in their basements, walllizards are completely harmless tohumans. They won’t bite unless cap-tured, and only the very largest maleshave the ability to even lightly break theskin if you let them bite. On the otherhand, they are voracious predators ofsmall insects and other arthropods. Mystudents and I examined the diets oflizards throughout their active season,and we found they eat a wide variety ofprey species, including familiar gardenpests like aphids, grasshoppers, caterpil-lars, and snails. They also successfullytackled more formidable prey such aswasps, bees, and large beetles. Malelizards tend to reach slightly larger bodysizes and have larger heads thanfemales; not surprisingly they tended toeat the bigger, more challenging prey,while females specialized on aphids.One female we studied had eaten 50aphids! The diversity of prey specieseaten by Long Island wall lizards wasquite close to that of their Italian coun-terparts, although, of course, the specif-ic prey species were different. Becausemany of the species eaten by wall lizardsare also non-native, and many of theirprey are considered garden pests, wecould conclude that the lizards have nonegative effect on the suburban ecosys-tems they currently inhabit on LongIsland.

There are more subtle ways thatthese new invaders could affect otherorganisms in their new home — if they

carried diseases or parasites with them,and these had spread to species here.There are a number of diseases knownto spread between different reptiles(including birds) and mammals — someof the most common are bacteria in thegenus Salmonella. Salmonella outbreaksare famous for popping up here andthere in human populations and quicklydisappearing, but they appear to bechronic in many turtle, lizard, and birdpopulations. They can be quite serious,causing severe illness and even death inhumans, and occasional massive dieoffsin wild birds. Very little work has beendone on diseases of wild reptiles in gen-eral, and no one has researchedSalmonella or any other disease in walllizards. The possibility exists that thelizards brought new species or newstrains or have become a new reservoirfor important diseases, but no evidencesuggests this is so, and no disease prob-lems have been linked in any way tothese lizards. However, anyone whohandles these or other reptiles shouldalways wash carefully afterwards.

A bit more is known about bothintestinal parasites and blood parasites ofreptiles, and wall lizards in Italy areknown to have both kinds of parasites.However, ecological theory suggests thatwe shouldn’t expect the wall lizards inNorth America to be carrying many para-sites, for three reasons. First, a small

sample of lizards is likely to carry only asmall sample of the total number of para-sites found in the lizard populations inItaly, so whatever parasites they may havehad in Italy, we should expect them to becarrying fewer parasites here. Second,many parasites depend on multiple hostsfor their life cycle, and odds are low thatany parasites the colonists brought withthem would find good replacements forthe other hosts they need. And finally,the “parasite release” hypothesis predicts

that any species that does well as aninvader does so in part because it is notheld back by the parasites it faced in itsnative land. Wall lizards are certainlydoing well in North America, so theyprobably aren’t carrying many parasites,if the hypothesis applies.

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Photo by Bill Davis. ©2003 Newsday, Inc. Reprinted with permission.

HOFSTRAHORIZONS17

Our lizards can be tests of thesehypotheses, but not much is knownabout lizard parasites. Lizard blood par-asites include the protozoans that causemalaria (genus Plasmodium); however,there are many kinds of Plasmodium, andeach kind restricts itself to only a fewhost species. Lizard Plasmodium are notgoing to infect people, but they mightinfect some other lizards. Because thereare no other lizards on Long Island, thisis only a minor concern. Plasmodiumalso require time in a mosquito host aspart of their life cycle. Given the factthat wall lizards are still not very abun-dant compared to other hosts that LongIsland mosquitoes have available, theodds are low that a mosquito will pickup a Plasmodium infection from one walllizard, and then later find another walllizard to feed on, and infect. Thus itseems unlikely that a lizard Plasmodiuminfection could persist on Long Island,even if the original lizards were infected.My colleagues and I have examinedhundreds of blood samples not onlyfrom Long Island wall lizards, but alsofrom the three other North Americanpopulations of introduced wall lizards,and none have had any trace of bloodparasites.

Reptiles are sometimes infectedwith intestinal parasites, includingtrematodes, nematodes, cestodes, andflagellates, and these are not nearly sohost-specific. In fact, some of these caninfect fish, turtles, birds, and mammals,so there is a possibility that the intro-duced lizards could have brought intes-tinal parasites that now infect local ani-mals, or that local animals have intestin-al parasites that now infect wall lizards.Unfortunately, very little is known aboutthe intestinal parasites of Italian walllizards in their home country, so wecan’t speculate on what the originalreleased lizards might have had withthem. Also, nothing is known about theparasites of Long Island reptiles, so wecan’t suggest what the wall lizards mighthave been exposed to here. However,my colleagues and I have examined thestomachs and intestines of more than1,000 wall lizards, from all four NorthAmerican populations, and found onlytwo nematode parasites, and those had

probably been ingested with insect prey.Both nematodes are members of NorthAmerican species common in birds, sothere’s no evidence that the wall lizardsbrought anything from Italy, and it does-n’t look like they’ve picked up muchhere either.

How do wall lizards survive ourwinters? Wall lizards range from thefoothills of the Alps in extreme northernItaly all the way south to the island ofPalermo off the southern tip of Italy, sodifferent populations have certainlyadapted to different climates. Ourgenetic work, however, shows that ourLong Island population comes from thevicinity of Rome. This makes sensebecause pet wholesalers in the 1960sand 1970s were shipping animals out ofRome, and they probably obtained localanimals. Rome’s summer temperaturesare actually quite similar to those ofLong Island — matching our averagetemperatures in June, July, and Augustalmost perfectly. However, our averagewinter temperatures are quite a bit cold-er, as it rarely gets much below freezingin Rome. The real differences are inextreme temperatures. Long Islandoften gets winter extremes of -4°F oreven colder, whereas Rome’s coldestnights, even in very cold years, bottomout around 23°F. So the Italian wall

lizards survive much colder tempera-tures on Long Island than their recentancestors experienced in Italy. How dothey do it?

They don’t do it by freezing. TheEuropean common lizard (Lacerta vivip-ara) is a close relative to the wall lizard,and it survives very cold winters by uti-lizing a series of physiological adapta-

tions that allow it to freeze solid withoutdamaging its tissues. This is a neattrick; few other vertebrates can do it.For example, when our body partsfreeze, we get frostbite and the frozentissue dies, in part because the frozencells burst. Lacerta changes its bloodchemistry so cells don’t burst. If wall

Mean temperatures in Italy and New York

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Filled triangles represent average monthly temperatures (°C) forRome, Italy, 1901-1930; filled squares represent mean monthly tem-peratures for Mineola, NY, 1948-2001; empty triangles representextreme minimum temperatures for Rome, Italy, 1901-1930; emptysquares represent extreme minimum temperatures for Mineola, NY,1948-2001.

Photo by Bill Davis. ©2003 Newsday, Inc. Reprinted with permission.

18 HOFSTRAHORIZONS

Russell Burke's longstanding interest inreptiles was a major influence in his decision topursue a career in biology. As a child, herecalls collecting local snakes and keepingthem in captivity. A major complaint growingup was that there were no lizards or venomoussnakes nearby, and he seized the earliest

opportunities to visit places in Florida whereboth were abundant. Today, he continues tofocus his research efforts largely on reptiles.

Professor Burke earned a B.S. in zoologyfrom Ohio State University, an M.S. in wildlifeecology from the University of Florida atGainesville, and a Ph.D. in biology from theUniversity of Michigan. He began teaching atHofstra as an assistant professor in 1996, andwas promoted to associate professor in 2002.Professor Burke teaches evolution, ecology,behavior and conservation biology.

He first began serious research on lizardswhile at the University of Michigan, when herecognized the advantages of lizards as studyorganisms: they are easy to observe both in thewild and captivity, they are short-lived, andoften abundant. These characteristics makethem excellent models for studies of naturalselection. The abundance of Italian wall lizardsnear Hofstra University actually contributed toProfessor Burke’s desire to teach here.

Because wall lizards are common close tocampus, they are an excellent species for intro-ducing Hofstra undergraduates to scientificresearch in the lab and in the field. Since1997, 10 undergraduates have completedresearch projects on wall lizards in ProfessorBurke’s lab, resulting in several publications.Despite the fact that the lizards are quite activearound people, many Hofstra students, evenhaving grown up in neighborhoods where thelizards are common, are unaware of their pres-ence. “One of the best things about taking stu-dents out in the field to study lizards is theirsurprise when they find that lizards have beenaround them all along and they never noticed,”he explains. This trend is likely to continue asthe lizards spread onto Hofstra campus — he’srecently found them at the Hofstra UniversityModel Bird Sanctuary. He predicts that thelizards will continue to spread over the Hofstracampus, startling students and visitors alike.“That awareness of the living world around us,often unexpected, makes everyone a biologist.”

lizards could do the same, then theycould easily survive cold Long Island win-ters. But our laboratory work shows thatthey don’t, so they must avoid freezing.

They avoid freezing on Long Islandby going deep underground, and notcoming out until the danger of freezingis long past. We have monitored theactivity of Long Island wall lizards, andwe’ve found that they’re quite differentfrom their Italian relatives. In Rome,wall lizards may be active any month ofthe year, even on warm days in January.In contrast, our wall lizards spendNovember, December, January andFebruary deep underground, quite safefrom freezing. Therefore they’re activefor a much smaller fraction of each year,and we’d expect that they grow moreslowly, reproduce less frequently, andreach maturity more slowly than in Italy.Unfortunately, there’s no Italian dataavailable to test that hypothesis. I’m hop-ing to spend some time in Italy next yeargathering data on their lizards, so we canmake better comparisons with ours.

Italian wall lizards might be anexample of an invasive species with lit-tle impact on their new homes. Thatdoesn’t mean I advocate spreading themaround deliberately — they’re spreading

just fine on their own and don’t needany help. They have not yet spread intoeven moderately natural habitats inNorth America, and they may yet turninto a problem when they do. It is cer-tainly hard to imagine how we couldstop them even if we wanted to. In themeantime, it should be noted that theintroduced wall lizard populations canhave some value. First, they can pro-vide useful data for evolutionary andecological model testing, especially withregard to theories dealing with howspecies will respond to new environ-ments. This is particularly important

when the new environment differs fromancestral environments in only a fewfactors, such as day length or minimumtemperature. Second, they can providedata useful for conservation. For exam-ple, concerns about the rare Aeolianwall lizard (Podarcis raffonei) have led tothe suggestion that reintroductions maybe needed in the future, and learningabout the successful and failed introduc-tions of its close relatives may be help-ful. Finally, wall lizard introductionshave occurred only in urban or subur-ban areas, and these ecosystems havefew species of native reptiles. Therefore,introduced wall lizards can provideexcellent opportunities for study byamateur biologists, because wall lizardsoften become abundantly common andthey are easy to observe. For me, theopportunities to watch and handle wildanimals in my neighborhood played akey role in my inclination to become abiologist. Wall lizards can provide theherpetological equivalent of watchingbirds at feeders, introducing studentsand other nonprofessionals to the basicsof scientific research. As the lizardsspread across the Hofstra campus, youcan expect my students to be takingnotes.

This is a cross section of a toe from an Italian wall lizard capturedon Long Island. The image shows bone rings laid down with eachwinter the lizard survived, just as a tree lays down annual growthrings. This adult male has survived at least five winters.