Pitt Island longhorn

Identification of Xylotoles costatus is difficult as it is very similar in appearance to another longhorn beetle found in the Chatham Islands, Xylotoles traversii. Both species are coloured black with a green bronze sheen, however it is likely that X. costatus has more of a bronze sheen than X. traversii. Of the two species X. costatus also has the more pronounced ridges on its wing cases. Generally X. traversii is the smaller beetle of the two, but the size of the two species can overlap. However, if a longhorn beetle specimen is found in the Chatham Islands that is greater than 16 mm in length it is likely to be X. costatus.

This species of longhorn beetle is usually found on the trunks of Coprosma chathamica at night. Recently dead or dying branches also attract adult beetles.

Xylotoles costatus was first described and named by Francis Polkinghorne Pascoe in 1875, based on male and female specimens collected by Henry H. Travers on Pitt Island. A type specimen is held at the Natural History Museum, London. The last known collection of this beetle, prior to its rediscovery, was by Thomas Hall who extensively sampled Pitt Island for beetles between 1906 and 1908. He collected three specimens which are now held in the New Zealand Arthropod Collection.