Family: Siricidae
Family common name: horntails
Subfamily: Tremecinae
Genus: Eriotremex Benson, 1943
Subgenera: none


The Siricidae are called “horntails” because of the Siricidae sawflies; on tergite 10 in females, sternite 9 in males ">cornus, a short spine at the apex of the abdomen. Females in the family also possess a long, conspicuous ovipositor. This is often mistaken for a stinger, but it is harmless to animals and used for drilling into wood. This habit has inspired the other common name of this family: “woodwasps” (Klass 1974).

Horntails of the genus Eriotremex are large and slender with a cylindrically shaped abdomen. The body is generally all black or black with yellow bands, giving a hornet-like appearance. Females are on average larger than males, but becasue of high variability in size among species, the sexes are best distinguished by the presence or absence of the long ovipositor (Schiff et al. 2012).


The genus includes 12 described species worldwide, with the highest diversity in Southeast Asia. In North America, there is only one species, the introduced Eriotremex formosanus (Schiff et al. 2012).

A key to North American species of Eriotremex is included in Schiff et al. 2012.

Diagnostic characteristics

specific characteristics for Eriotremex formosanus:

May be confused with

Eriotremex can be confused with other Siricidae, especially Tremex, because of the similar coloration. They can be distinguished from other genera in the family by the long and distinctively flattened antennae, lack of ridge on gena behind the eye, and dense, long hairs on the body (Smith 2010).

Exotic pest species of concern

Siricidae are commonly intercepted in wood packing materials at ports of entry. The potential of larval stages to persist and develop for multiple years increases the potential of successful establishment from improperly treated or disposed of wood material.

Eriotremex formosanus is native to southeastern Asia, specifically Taiwan and surrounding regions, and was introduced into southeastern United States in 1974 in Florida and Georgia. The species is well established, and is now the most common woodwasp of Florida (Li and Hulcr 2015). However, its status as a pest is not certain, as the preferred hosts tend to be dead or dying trees. A recent concern with this species is potential displacement of the only native siricid woodwasp to also utilize angiosperms as host, Tremex columba (Ulyshen and Hanula 2010).

Host associations

Eriotremex is not well studied in its native range and its hosts are unknown. In North America, E. formosanus has been documented on Quercus spp. (oak), Carya spp. (hickory), and Liquidambar styraciflua (American sweetgum). The species has been observed flying in forests dominated by Pinus spp. (pine), but no evidence of successful development in pine is confirmed (Li and Hulcr 2015).

Life history

Female Eriotremex harbor symbiotic basidiomycete fungi in abdominal glands called mycangia. During oviposition, the tree is inoculated with the fungus, which begins to decompose the surrounding wood. Larvae feed on the fungus and in the process bore galleries through the wood. The fungal symbiont for E. formosanus is Cerrena unicolor. Females reserve mucus in additional abdominal glands, but the function of these reservoirs is not well understood (Schiff et al. 2012).

Larvae are creamy white and grub-like in appearance with a dark head capsule. As with adults, larvae possess a short dorsal horn on the posterior end of the body. The larvae bore galleries while developing through 6–12 larval instars, depending on food availability, until pupation and subsequent emergence. Throughout this process, the larvae use their horn to pack the tunnel behind them with sawdust. Emergence holes are perfectly circular. The fungal symbiont is carried in specialized organs in female larvae that develop into the mycangia after metamorphosis (Schiff et al. 2012).

Adult Siricidae are not well studied (Schiff et al. 2012). Information on Eriotremex is especially lacking despite its potential importance as an invasive species. Observations in the United States suggest a preference for dead trees, and particularly for standing dead trees, or snags, as a host (Ulyshen and Hanula 2010).


World: Except for E. formosanus, the genus is restricted to Asia and ranges from eastern India through China, Japan, Taiwan, and Vietnam, and as far east as Papua New Guinea (Li and Hulcr 2015). Specimens are rarely collected in this range (Smith 2010).

North America: The single species in North America is common in the southeastern United States (Schiff et al. 2012). Eriotremex formosanus ranges as far north as Virginia and as far west as Arkansas. Interceptions have been made farther west, including one in Utah, and several in Hawaii, but there is no evidence that it is established (Li and Hulcr 2015, Janis Matsunaga pers. comm. 2020).

Map data from: (26 June 2019) GBIF Occurrence Download Eriotremex and the Smithsonian National Museum of Natural History (USNM)

Details about data used for maps can be found here.

Eriotremex formosanus female lateral habitus; photo by Q. Baine, WSDA

Eriotremex formosanus female lateral habitus; photo by Q. Baine, WSDA

Eriotremex formosanus female dorsal habitus; photo by Q. Baine, WSDA

Eriotremex formosanus female dorsal habitus; photo by Q. Baine, WSDA

Eriotremex formosanus female face; photo by J. Orr, WSDA

Eriotremex formosanus female face; photo by J. Orr, WSDA

Eriotremex formosanus male face; photo by J. Orr, WSDA

Eriotremex formosanus male face; photo by J. Orr, WSDA

Eriotremex formosanus wings; photo by Q. Baine, WSDA

Eriotremex formosanus wings; photo by Q. Baine, WSDA