The species is common in the North Island of New Zealand. Perithecia are free, cuneate and lighter coloured than the stalk. A small sterile apiculate tip is always present.

In the herbarium of the Commonwealth Mycological Institute there is a specimen ex herb. Sydow from Chile (ex P.A.Hollenmeyer No. 1765) labelled C. robertsii; this superficially resembles New Zealand material but perithecia and asci are smaller.

Kobayasi (1941) listed the species as C. larvarum Westwood. Westwood (1836) did not publish this combination, but merely stated that "he believed that a Clavaria sp. parasitised the caterpillar" and in a footnote added that this species was described by Sir W.Hooker in Icones Plantarum as Clavaria lavarum. Hooker, however, described and illustrated this species as Sphaeria robertsii. Berkeley mentions the name Sphaeria forbesii when quoting a letter from J.E.Gray, but did not append a description. No material is filed under C. hugelii in the herbarium of the Royal Botanic Gardens, Kew, but in the folder of Cordyceps robertsii there is a collection labelled Sph. robertsii Hook. - hugelii Cke., N.Z. This collection, and Corda's illustration and description. are comparable with Cordyceps robertsii. Massee (1895) described a form which differs from the type in that perithecia are flask-shaped and with a long slender neck; he named this variety C. hugelii var. neglecta Massee. At Kew no collection is filed under this name, but there is one labelled "Sphaeria robertsii - ? Cordyceps neglecta Massee, N.Z., Colenso. This is a typical specimen of Cordyceps robertsii parasitised by a species of Torrubiella and is presumably the type of Massee's variety. Kobayasi (1941) listed this form as C. larvarum (Westwood) Olliff var. neglecta (Massee) Kobayasi and described it as a synonym of C. robertsii (Hook.) Gray var. neglecta Massee.

Myers in Cunningham (1921) stated that "practically all the earlier naturalists accepted without question the current belief that the host of this species was Hepialus virescens Dbd. as it was the only larva large enough to coincide with the vegetable caterpillar . . . Hudson was the first to point out the improbability of the arboreal Hepialus as a host seeing that the infected larva was invariably found underground . . . . " Later Myers stated that it was probable that the usual host of C. robertsii is Porina (Oxycanus) dinodes Myers in the South Island and P. (Oxycanus) enysii Buller in the North. Parasitised larva of Hepialus virescens have been collected, but unfortunately the fertile portions of the stroma are missing. The vegetative parts and the conidial form suggests that it. may be a different species. In Kew herbarium all specimens are parasitic on typical larva of Oxycanus sp. although in many cases they were labelled Hepialus virescens.