The ranges of native species of Siricidae are grouped in six major distribution patterns. The transamerican distribution pattern extends from the Atlantic to the Pacific coasts usually centered in the boreal zone from Alaska to Newfoundland. The following species have this distribution pattern: S. nitidus, U. flavicornis and X. melancholicus. Occasionally a species with a more temperate range will be found from British Columbia to Newfoundland. The following species has this distribution pattern: U. albicornis.
Ranges restricted to regions father south (usually the southern boreal zone or further south) are divided into eastern and western distribution patterns.
The eastern distribution pattern varies greatly in extent. A range could extend as far west as east of the Cascades Mountains. Only one species shows such a wide range: Tremex columba. This species is centered in eastern Northern America but one color form occurs from the eastern edge of the prairie ecotone west to the eastern edges of the Great Basin. A more typical eastern range is one that extends from the Atlantic coast between Nova Scotia and the Gulf of Mexico to at most regions east of the Rocky Mountains and north of the prairie ecotone. The following species have this distribution pattern: S. cyaneus (south of New York the range is restricted to high Appalachian Mountains), S. nigricornis, U. cressoni and U. taxodii (this species was previously known to occur only in southeastern United States, but following its recent discovery in Ontario its range now fits with the above distribution pattern).
The western distribution pattern occurs from the Rocky Mountains to the Pacific coast and also includes the coniferous zone of highlands in the prairies such as the Cypress Hills in Alberta and the Black Hills in South Dakota. The following species have this distribution pattern: S. abietinus, S. areolatus, S. behrensii, S. californicus, S. longicauda, S. varipes, U. californicus, X. indecisus, and X. caudatus. These species extend widely from British Columbia down to California and probably northernmost Mexico south of California. Most have ranges extending north into southern British Columbia, but the ranges of S. abietinus and S. californicus extend as far north as southern Yukon or northernmost British Columbia. The range of X. tarsalis is restricted to the Pacific coast.
Species in southwestern United States that occur east of the Sierra Nevada and as far north as southern Utah and Colorado correspond to a variation of the western distribution pattern. All are probably found in Mexico at least along the Sierra Madre Occidental where there is a rich diversity of conifers. The following species show this distribution pattern: S. obesus, S. xerophilus, S. mexicanus, X. chiricahua and X. morrisoni.
Species found south of the Isthmus of Tehuantepec are part of another distribution pattern probably associated with the Guatemalan highlands. Only X. tropicalis has this pattern.
The Caribbean distribution pattern in the Greater Antilles is the most unusual. So far only two species have this pattern pattern: S. hispaniola (pine forests above 1000 m) and T. cubensis (low elevation).
The association of Siricidae with tree trunks and wood have pre–adapted them for worldwide travel, mostly by means of human activity involving international transport of wood products and untreated logs. Their concealed larvae and frequently a multi–year life cycle means they usually remain unnoticed until they become established in areas far outside their native ranges. The primary example is Sirex noctilio, native to the Palaearctic region, which has become established in pine plantations in Australia, New Zealand, southern South America, South Africa and, most recently, eastern North America. Numerous other alien siricids have been intercepted at Western Hemisphere ports of entry. The distribution patterns of the species that are now established in the new area are in flux because all are still expanding their ranges.
Five exotic species from the Palaearctic and Oriental regions have become established in the Western Hemisphere: Sirex noctilio in southern South America (Iede et al. 1998) and eastern North America (Hoebeke et al. 2005), Urocerus sah in eastern North America (Smith 1987), Urocerus gigas in Chile and Argentina (Smith 1988), Eriotremex formosanus in southeastern United States (Smith 1975b, 1996), and Tremex fuscicornis in Chile (Baldini 2002). Urocerus flavicornis has been reported from Brazil (Ries 1946) but it has not been confirmed since.
Interceptions at ports of entry give an idea of the movement of species. Benson (1943, 1963) reported Sirex areolatus, S. cyaneus, Urocerus albicornis, U. californicus, and U. flavicornis, as adventive but not established in Britain. We have seen and studied numerous intercepted specimens from Canada, New Zealand and United States. No doubt there are many other records of interceptions awaiting discovery in collections of various countries. We summarize data from Canada and the United States, based on identified adults found in collections. In the United States, records for the past 40 years (DRS unpublished) indicate that more than 12 species have been intercepted in incoming wood, dunnage, or other wood products. They originated from more than 20 countries and were intercepted at 30 different ports of entry, mostly along the eastern and western seaboards, and a few at the Mexican border. Many unidentified intercepted larvae could include additional species. Other than Sirex noctilio, the only exotic Siricidae known to be established in the United States are Urocerus sah and Eriotremex formosanus. It is surprising that more species of Siricidae have not become established because interceptions include species of Sirex, Urocerus, Xeris, and Tremex. At least six species of Sirex have been intercepted from Europe, eastern Asia, and Mexico. Based on adults, the earliest interception record for S. noctilio is 1978. Since then, it has arrived from at least six European countries and been intercepted at seven different ports along the eastern seaboard. Urocerus gigas is the most commonly intercepted species of Urocerus, mostly from European countries. Western Palaearctic and Asian species of Xeris have been intercepted at eastern and western ports; and several species of Tremex, mostly from eastern Asia, have been intercepted at western ports.
Within Canada and United States, siricid wasps have been found outside their native range emerging from imported structural wood. Eastern United States records for Sirex areolatus, S. behrensii, S. longicauda, and S. varipes from homes and other buildings result from importations in wood from the western United States (Smith 1979, Smith and Schiff 2002). They often emerge from structures several years after wood is used for construction. Records indicate that only S. areolatus may have become established in the southeastern states.