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BACKGROUND: Explanations for the ecological dominance of ants generally focus on the benefits of division of labour and cooperation during foraging. However, the principal innovation of ants relative to their wasp ancestors was the evolution of a new phenotype: a wingless worker caste optimized for ground labour. Ant workers are famous for their ability to lift and carry heavy loads, but we know surprisingly little about the morphological basis of their strength. Here we examine the consequences of the universal loss of flight in ant workers on skeletomuscular adaptations in the thorax for enhanced foraging on six legs. RESULTS: Using X-ray microcomputed tomography and 3D segmentation, we compared winged queens and wingless workers in Euponera sikorae (subfamily Ponerinae) and Cataglyphis savignyi (subfamily Formicinae). Workers are characterized by five major changes to their thorax: i) fusion of the articulated flight thorax (queens) into a rigid box optimized to support the muscles that operate the head, legs and abdomen, ii) redesign of internal cuticular structures for better bracing and muscle attachment, iii) substantial enlargement of the neck muscles for suspending and moving the head, iv) lengthening of the external trochanter muscles, predominant for the leg actions that lift the body off the ground, v) modified angle of the petiole muscles that are key for flexion of the abdomen. We measured volumes and pennation angles for a few key muscles to assess their increased efficacy. Our comparisons of additional workers across five genera in subfamilies Dorylinae and Myrmicinae show these modifications in the wingless thorax to be consistent. In contrast, a mutillid wasp showed a different pattern of muscle adaptations resulting from the lack of wing muscles. CONCLUSIONS: Rather than simply a subtraction of costly flight muscles, we propose the ant worker thorax evolved into a power core underlying stronger mandibles, legs, and sting. This contrasts with solitary flightless insects where the lack of central place foraging generated distinct selective pressures for rearranging the thorax. Stronger emphasis is needed on morphological innovations of social insects to further our understanding of the evolution of social behaviours.

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Velvet ants (Mutillidae) are solitary wasps whose larvae act as ectoparasitoids of encapsulated immatures of other insects, especially other solitary Hymenoptera (Luz et al. 2016). The natural history of most mutillids is unknown; for example, only 2-3% of the species have their hosts reported (Brothers 1989). Apidae species, however, are among the hymenopterans most commonly parasitized by velvet ants, with over 30 recorded cases in literature involving different genera of both host and parasite (Luz et al. 2016).

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A list of 12 species in nine genera occurring in Hong Kong is given. The hitherto unknown male of Bischoffitilla lamellata (Mickel, 1933) is described and illustrated. Six species are newly recorded from Hong Kong. The current number of known mutillid species of Hong Kong is doubled from six to 12.

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Velvet ants are a group of parasitic wasps that are well known for a suite of defensive adaptations including bright coloration and a formidable sting. While these adaptations are presumed to function in antipredator defense, observations between potential predators and this group are lacking. We conducted a series of experiments to determine the risk of velvet ants to a host of potential predators including amphibians, reptiles, birds, and small mammals. Velvet ants from across the United States were tested with predator's representative of the velvet ants native range. All interactions between lizards, free-ranging birds, and a mole resulted in the velvet ants survival, and ultimate avoidance by the predator. Two shrews did injure a velvet ant, but this occurred only after multiple failed attacks. The only predator to successfully consume a velvet ant was a single American toad (Anaxyrus americanus). These results indicate that the suite of defenses possessed by velvet ants, including aposematic coloration, stridulations, a chemical alarm signal, a hard exoskeleton, and powerful sting are effective defenses against potential predators. Female velvet ants appear to be nearly impervious to predation by many species whose diet is heavily derived of invertebrate prey.

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A new species, Petalomium barrosbattestiae sp.n. (Acari: Neopygmephoridae), associated with Traumatomutilla rubroguttata (Hymenoptera: Mutillidae) from Brazil, is described. Some new host records of Trochometridium tribulatum Cross, 1965 are reported, including the first record of this species in Brazil. The association between mites of the genus Petalomium and velvet ants is reported for the first time.

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An aggregation of two males of Timulla bitaeniata (Spinola, 1841), three single males T. rufogastra (Lepeletier, 1845) and another two males T. rufogastra (Lepeletier, 1845) in copula with two females of T. eriphyla Mickel, 1938 is documented, described and discussed. A new synonymy is proposed for Mutilla rufogastra Lepeletier de Saint-Fargeau, 1845 [=Timulla (Timulla) eriphyla Mickel, 1938, syn. nov.] based on the mating pairs.

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The male and female of Ephuta icema Casal, 1969 are reared from the host Auplopus subaurarius Dreisbach, 1963 (Hymenoptera: Pompilidae) that allow to unit both sexes for this mutillid and describe hitherto unknown male. A review of all the previous host records for the genus Ephuta Say, 1836 is given.

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ABSTRACT A review of bee species used as hosts of mutillid wasps in the Neotropical region is presented. Three new confirmed host records are provided for the mutillid species Hoplomutilla biplagiata Mickel, 1939, Pappognatha limes Mickel, 1939, and Tallium aracati Casal, 1962. Two potential host records are provided for Euspinolia rufula Mickel, 1938 and Lophomutilla inca Fritz and Pagliano, 1993. Additionally, Mutilla hoplitiformis Strand, 1909, is transferred to the genus Darditilla. Correlations between host nesting habits and female mutillid morphology are discussed. Lastly, all known confirmed and potential host records in the Neotropical region are compiled.