Their large size is a typical and obvious characteristic in the family, with lengths up to 30 mm (1.2 in). The following distinct features are diagnostic characters, based on research by Ronquist and Liu and Nordlander.
The genae are swollen and pronounced. The female antenna consists of 11 segments, while the male antenna consists of 13 segments. A large portion of the pronotum is well developed, called the dorsal pronotal area, with scutellar processes. The marginal cell of the forewing is elongated and thin. The gaster is long and pronouncedly compressed laterally. The seventh tergum is large in females. An apical tubular process is present on the second tarsomere of the hind leg. The metafemur is short, no longer than the metacoxa.
Ibalia leucospoides, note the compressed gaster
Ibalia rufipes with Ibaliidae characteristics marked out
The female lays the egg by oviposition through the oviposition shafts created by Siricidae, and the egg is deposited inside a siricid larva. In the species Ibalia drewseni Borries and Ibalia leucospoides (Hochenwarth), host detection by symbioticfungus in the siricid has been observed.
The larva lives it in its first instars as an endoparasite, and later exits the host and lives on the remaining host tissues. The primary instar is polypodeiform with paired appendages on segments 1–12, and in the second to fourth instars, the appendages are lost. Until the terminal instar, the remaining cauda is gradually decreased.
Several species in the genus Ibalia have been introduced to South America, Australia, and New Zealand, sometimes to control previous accidentally introduced Siricidae species parasitizing economically important pine forests. Species used are, for example, Ibalia leucospoides and I. ensiger Norton. Results from introductions vary, and studies of long-term effects are lacking, but in some areas, the effects on pests have been successful; Siricidae populations have been strongly limited. They are most effective in combination with other parasitoid organisms, such as nematodes.
^E. Alan Cameron (2011). "Parasitoids in the management of Sirex noctilio". In Bernard Slippers, Peter de Groot & Michael John Wingfield. The Sirex Woodwasp and its Fungal Symbiont: Research and Management of a Worldwide Invasive Pest. Springer. pp. 103–117. ISBN978-94-007-1959-0.