Description & Statistics
The subfamily Crabroninae contains a large number of species of small parasitoids that build their nests in hollow stems, burrows in the soil or abandoned wood galleries. The latter are usually those of beetle borers, and may be further enlarged by the new occupant to provide cells for its brood. The nests are of two types, one being linear and consisting of a row of cells, the second having lateral galleries branching from the main tunnel. Prey are exceedingly varied, ranging from mites and spiders to adult Coleoptera, Diptera, Homoptera, Ephemeroptera, Lepidoptera, Hymenoptera and Diptera (Clausen 1940/1962). The subfamily is not wholly beneficial because of the attack on spiders and some parasitic and predaceous Hymenoptera and Diptera. Syrphid flies are frequently attacked, and in Europe Lindenius pygmaeus Rossi provisions its cells with chalcidoids of the genus Pteromalus. There is no obvious consistency in the selection of prey by the various species, as the species of a single genus may utilize Diptera, Hymenoptera or Coleoptera. A single parasitoid species may limit itself to only one sex of the host, while the opposite extreme is found in examples of species preying on several orders (Hamm & Richards 1926).
The first cell to be provisioned is that one situated farthest from the nest entrance, and the egg is usually laid on the first prey placed in each cell. However, in Crabro brevis Lind. oviposition occurs only after the full complement of beetles has been stocked in the cell. Species in the genus Oxybelus are somewhat small wasps that make their burrows in sandy places and provision the cells with flies. Oxybelus quadrinotatus Say carries prey in an inverted position beneath the body, the head grasped by the hind pair of legs in such a position that the entire abdomen projects caudad beyond her body (Peckhams 1898). Flies are killed at capture. In other species death ensues when the thorax is crushed with the mandibles.
Peckhams (1898) studying Hypocrabro stirpicola Pack., noted that activity continued during nighttime. The flies used in provisioning the nest were in the Calliphoridae and Anthomyiidae, being dead at the time of storage. Xestocrabro sayi Ckll. (= sexmaculata S. & F.) does not harm its prey, because when cells are opened the flies and gnats are active, some being able to escape. Crabro brevis Lind. stores its nests with adult chrysomelid beetles in the Halticinae (Grandi 1925). Those found in a cell may represent several species or even genera, and in different localities the wasp may specialize on different species. The nest comprises 6-10 cells, each of which is provisioned with 12-25 beetles. Some species of the genus have been known to carry prey impaled on the sting. In Europe, Ceratocolus alatus Panz., stores its nests with adult moths of Phlyctaenodes sticticalis L., and the cocoons are made largely of the prey's wings, the habit of using remains of prey in the cocoon being common to many species. Tracheloides hicksi Sandh. has been found to attack ant columns on tree trunks, the female parasitoid seizing an ant and flying away with it to a nearby branch, where it is stung.
This group was reported as a subfamily of Crabronidae in the Apoidea by Finnamore & Michener (1993). They are cosmopolitan with over 1,302 species known as of 2000. They are rather uniform in color, size and shape. Adults are generally black or black with yellow or white markings. They stock their nests with Diptera. In North America there are around 200 species in 14 genera (Finnamore & Michener 1993).
The subfamilly Crabroninae is the most diverse group in the wasp family Crabronidae, containing over 100 genera. The subfamily consists of solitary, predatory wasps. The adult females of many groups dig tunnels in the ground for nesting, but others use different techniques, including the construction of tube-like mud nests (e.g., Trypoxylon politum).
As with all other sphecoid wasps, the larvae are carnivorous; females hunt for prey on which to lay their eggs, supplying the larvae with paralyzed, living prey when they emerge.
A key reference is Bohart & Menke (1976).