Genus Physocephala

Physocephala Schiner 1861

7 spp. in our area(1)

5-14 mm(1) (guide photos)

Adults resemble solitary wasps in general shape and color. They have a petiolate abdomen (i.e. with a long, narrow second segment...followed by broader, shorter ones). The proboscis is hinged near the base, beyond which it is long, straight and needle-like, projecting forward well beyond the face. The antennae are also long and straight, positioned close together, and point forwardly-upward (i.e. are porrect).

Physocephala are often confused with Physoconops, which they closely resemble...for details on distinguishing the two, consult the "See Also" section below.

Terms commonly used to describe and identify Physocephala species are illustrated and defined in the following two labelled image posts:

       

A summary of key characters, with their various states and associated species, are listed below. Note that some species exhibit variable states for certain characters, and so may be listed more than once per line:

Worldwide, incl. most of our area

Generally most places where the aculeate hymenoptera used as larval hosts can be found (e.g. flowery areas for bees, sandy areas for bembecines, etc.).

Adults fly from late spring to late summer.

Larvae are parasitiods of various Apoidea/Sphecoidea & Vespidae; Physocephala have been recorded parasitizing Anthidium, Anthophora, Apis, Bombus, Centris, Eucera, Halictus, Megachile, Nomia, and Xylocopa. [See (2) & Gibson et al(2014)]

Adults feed on nectar of flowers.

The larvae of Physocephala are parasitoids of various aculeate hymenoptera. Adult female Physocephala will pounce on a hymenopteran host while it's visiting flowers or in flight (cf. 3rd paragraph here). Oviposition is accomplished by using a rapid opposing-motion of the female's theca and hook-like 7th abdominal segment to pry open the host's tergites (somewhat like a "can-opener") and then insert an egg into the abdomen.

The egg subsequently hatches within the host and begins feeding...first on haemolymph, and later on internal tissues...eventually killing the host (i.e. it's a parasitoid). This usually takes 10-12 days, though a study in Alberta showed that bumble bees parasitized by P. texana had the same lifespan as unparasitized individuals (Otterstatter et al. 2002)(3).

Bumblebee hosts have been documented to bury themselves under dirt before dying, a behavior presumably induced by the Physocephala larva, which benefits thereby from having a safer underground environment in which to overwinter before pupating and eclosing the following spring.

As with all members of Schizophora, the emerging adult rhythmically inflates its ptilinum to break out of its puparium...and, in Physocephala, also to break out of the host's corpse as well as to dig to the surface. (Video of emerging P. tibialis, from Gibson et. al.(2014).)

Once out of the ground, it finds a place to perch while it expands its wings (by pumping haemolymph into them) and "cures" (i.e. dries and hardens its exoskeleton).

Adults then go about mating, and females seek out hosts...repeating the cycle.

When at rest Physocephala (like many conopids) often wave their forelegs above their heads...presumably to simulate the appearance of the common behavior of hymenopteran antennal movements...and thus re-inforce their protection through wasp-mimicry. Photos will often capture conopids with their forelegs held up in the air.

                 

                 

                 

To ascertain a true (potential) mating pair (or trio, etc), check for the "hook" & theca of a female for the one on the bottom of the pair (or "pile")...as in the posts below:

               

...note the last image above is a bit tricky, since the "one on the bottom" has her abdomen "in the middle"! When a mating pair is actually en copulo (vs. a male simply perched atop female) the theca of the female is usually held pointing conspicuously outward, as in the posts below:

               

The preceding posts suggest the theca is not truly part of the genitalia (as some references assert) as it appears to play no role in copulation and to be solely an adaptation for oviposition.

         

Wing Venation In Physocephala, the anterior crossvein (denoted "r-m" in the diagram below), is located well beyond the middle of discal cell (denoted "dm"); and the discal cell is strongly "indented" just basad of the crossvien r-m. Note that the tiny crossvein bounding the discal cell at its base is usually hard to see, but it is always just beyond where the vein on the lower edge of the discal cell meets cell "cup" (cf. 2nd diagram below):

In Physoconops, the crossvein r-m is near or before the middle of cell dm; and the discal cell is typically less strongly indented basad of crossvein r-m, and often more-or-less straight along its upper edge:

[

Hind femora In Physocephala the the hind femur is irregularly thickened and widest in its basal portion:

In Physoconops, the hind femur has a more uniform thickness and is widest near the middle:

Note that the hind femur character is best employed with a profile view. From some angles the basal swelling in Physocephala may not be clearly apparent.

To be confident of an identification, it's best to have a number of characters available for verification, since some may be difficult to interpret (or even "not work", due to variation), or they may not be visible. While the above characters are the primary ones used to separate Physocephala and Physoconops in most keys, and are presumably the most consistent and dependable ones, the following additional characters are also useful in distinguishing these two genera:

Video of a Physocephala eclosing from a host bee pupa from Gibson et. al(2014).

Revista Brasileira de Entomologia. Larval development of Physocephala (Diptera, Conopidae) in the bumble bee Bombus morio (Hymenoptera, Apidae)