[2] They differ from other parasitic wasps in their intensely aggressive behaviour during invasion and occupation of the host colony.

[3] Several morphological adaptations such as bigger body parts and highly curved stingers are present in these wasps to aid their aggressive parasitic behaviour.

[7] Until recently the Nearctic population was considered to be the same species, and appears in all of the literature before 2012 as V. austriaca,[8] though some sources are not yet updated; see.

As an adaptation to its parasitic lifestyle, V. infernalis has a large, heavily curved stinger; this curving allows the parasitic wasp to puncture through the intersegmental membranes of host colony workers who are defending their nests.

Irregular margins and narrow yellow marks on the scape are often used to identify Vespula infernalis.

As an obligate parasite, Vespula infernalis lacks a worker caste and cannot build their own nests or feed their own offspring.

Near the dorsal edge of V. infernalis mandibles, there is a fourth marginal tooth whereas the host, V. acadica has three.

[3] When a female V. infernalis invades a host's nest such as V. acadica during the queen-reared worker stage, the usurpation can be divided into two phases.

The parasite, if successful, will use its stinger to paralyze the head, thorax, and legs of the host queen.

In one experiment, a V. infernalis female was allowed to invade a Vespula atropilosa colony.

Injuries to the queen include but are not limited to broken antennae and injured fore and hind-leg.[when?

While there is still tension, the inquiline typically does not sting the workers and does not engage in egg eating (oophagy).

[5] This display of dominance by the parasite over the host workers is more common during early colony occupations and absent later on.

The parasite displays mauling behaviour: it grabs the workers with its legs and chews on their dorsums.

Furthermore, the parasite also displays mauling behaviour after trophallaxis, which it initiates by soliciting and chasing a worker.

Normally if workers were ovipositing then there would be higher levels of aggression between them, but mauling behavior tends to be reduced instead.

Another indication is that parasites are observed to patrol cells frequently, defending oviposition sites.

[9] While other wasp queens depend on secretions from larvae for food, V. infernalis obtain their nourishment in the liquid form through solicitations and trophallaxis of host workers.

In an experiment where the oily venom extracted from V. infernalis was injected into Vespula pensylvanica workers, the Lethal Dose (LD50) value was between 20 and 30 mg/kg.