Vollenhovia emeryi
Vollenhovia emeryi is one of the more recent ants to have established in North America. The first record of this Japanese transplant came from Stefan Cover of Harvard’s Museum of Comparative Zoology. Cover discovered the species in 1986 while sampling for ants in Washington, DC. Vollenhovia species tend to be generalists and the native range of the genus is restricted to Asia, northeastern Australia, and the Pacific Islands, and are not generally thought of as successful tramp ants.
How then did this demure little species come to arrive in the capital city of the United States? The answer might be linked to a tale often told of that city’s namesake, George Washington. Legend has it that when George Washington was a six-year-old lad he chopped down a cherry tree. When confronted by his father, young George replied, “I cannot tell a lie, father, you know I cannot tell a lie! I did cut it with my little hatchet.”
Cherry trees may, in fact, have been how Vollenhovia emeryi became introduced into the United States. Japan has gifted the cities of Washington DC and Philadelphia thousands of cherry trees during the past century, many of which were planted in localities where V. emeryi is known to occur. Dan Kjar raises the possibility that colonies of these little ants stowed away in the rootballs of the cherry trees, and have slowly been expanding their range along the riparian habitats of the District of Colombia, Virginia, Maryland, and Pennsylvania ever since.
Diagnosis of worker among Antkey species. Worker caste monomorphic. Head shape roughly ovoid. Antenna 12-segmented. Antennal club 3-segmented. Antennal scapes not conspicuously short; easily extended beyond eye level; do not extend beyond posterior margin of head. Antennal insertion not surrounded by a raised sharp-edged ridge Antennal scrobe lacking. Eyes medium to large (greater than 5 facets); distinctly less than half head length. Posterolateral corners of head unarmed. Frontal lobes do not obscure face outline between mandible and eye; relatively far apart so that the posteromedian portion of the clypeus, where it projects between the frontal lobes, is much broader than one of the lobes. Mandibles triangular. Mesosoma with erect hairs. Pronotal spines absent. Propodeum lacking spines or teeth. Slope of mesosoma gradual. Waist 2-segmented. Petiole with a distinct and upright node; lacking peduncle; with large subpetiolar process. Postpetiole attached to lower surface of gaster.
Vollenhovia emeryi is the only ant species with both an unarmed propodeum and an apedunculate petiole that is introduced to or commonly intercepted in the United States. these two characters, especially when combined with the large subpetiolar process, should make it easy to distinguish. The subpetiolar process can be difficult to observe, however, because it is on the anterior portion of the petiole and often requires the petiole to be lifted before a good view can be obtained. Vollenhovia emeryi can be confused with short-spined native Temnothorax species, but the subpetiolar process will reliably separate it.
Native range. Japan
Introduced range. USA: Philadelphia, Maryland, Washington, D.C.