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KEY WORDS: Ground nesting bee, parasitism, nest defense
The Mutillidae or velvet ants are aculeate wasps with many species characterized by bright aposematic coloration (Hurd, 1951). In the United States, these wasps occur in a variety of habitats, often abundant in semi-arid to arid regions of the country (Blake, 1886). The wingless females are often encountered wandering on the ground searching for host nests (Brothers et al., 2000). Approximately 4,200 species of velvet ants have been described and there may be at least 10,000 species worldwide (Brothers, 1989; Lelej and Brothers, 2008). Surprisingly, little information on the biology of velvet ants is known. Only about 3% have confirmed host records (Brothers et al., 2000). Recently, a review of bee hosts of mutillids for the Neotropical Region was compiled (Luz et al., 2016).
The first biological account of a mutillid is that of Christ (1791) (Mickel, 1928), who observedMutilla europaea Linnaeus, 1758, inside a bumblebee nest. He noted that Bombus (Apidae) and the mutillid were not aggressive toward each other. It was believed that they shared the same nest. However, 50 years later subsequent authors observed that M. europaea was indeed a parasitoid (Brothers et al., 2000).
While observing the nesting activity of a colony of the North American cactus bee, Diadasia rinconis Cockerell, 1897 (Apidae) (sensu Adlakha 1969) in northern Colorado (Larimer Co., Colorado, Dutch George area, off of Hwy 14, 1 July 2017), I saw a female in flight with no pollen load, a possible "floater" (Jander, 1999), which apparently noticed a female velvet ant, Pseudomethoca propinqua (Cresson, 1865) (Fig. 1) entering the burrow entrance of a D. rinconis nest. The bee suddenly accelerated in entering the burrow, apparently grasping the velvet ant...