Subject: unknown Hymenopterid
Location: Sherman Oaks, California 91423
March 15, 2014 9:18 pm
Hi. About a dozen of these largish Hymenopterids (4 wings) are flying during the day when the sun is shining on our outdoor patio, circling around; in particular they seem to like some ornamental hollies, but I’ve never seen them land for longer than a second or two. The bugs aren’t aggressive, and if they bump into you they don’t attack. My next door neighbor says that they are on their lawn, so perhaps they are a “not quite solitary” bee group. I don’t recall ever seeing this kind of bug around here before.
I captured one and put it in the freezer which killed it. I’ve attached three photos. The waist is somewhat constricted. Head to tip of abdomen 22mm. At least 11 antennal segments, front wings 3 closed cells. Abdomen 6 or so segments.
We believe this is a male Scarab Hunter Wasp in the family Scoliidae, possibly Campsomeris tolteca, which is pictured on BugGuide. This is a highly sexually dimorphic species, with the appearance of the female being so different from that of the male that she appears to be a different species. Alas, BugGuide does not have any species specific information, but the genus page on BugGuide does provide this information: “Eric Eaton has pointed out in comments under various photos of Scoliids that there is considerable taxonomic confusion in this family, so that has to be a caveat in any photo identified as to genus here. According to Nick Fensler: The females Campsomeris as well as other members of the subfamily Campsomerinae are predators on white grubs (Scarabaeidae), using these larvae as food for their young. Unlike sphecids, eumenines, and pompilids these wasps do not appear to have any type of prey transportation and dig to the ground-dwelling beetle larvae, sting it to paralyze it, and then lay an egg. They may dig around the grub to form a small cell. Since they use this nesting strategy they are often seen flying low to the ground (searching) in a figure eight pattern (but the flight pattern gets more erratic when they “smell” something). The adults use nectar as a food source and are common on flowers.” Male wasps cannot sting as the stinger in the female is a modified ovipositor. Since they are interested in your neighbor’s lawn, we suspect there is a significant population of Scarab Beetle grubs beneath the surface. Females are searching for prey that act as food for her offspring, while males may be patrolling for mates.
You may also visit Eric Eaton’s blog, Bug Eric, for more photos on male Scarab Hunter Wasps.
Hi Daniel. Thanks so much for identifying the scarab hunter wasp. Today I finally saw the even larger female (photos attached). A few years ago 3 large trees were removed from the neighbor’s property in the same area where these wasps are flying. Could be that the males are emerging from the ground, and maybe the large number is due to the significant availability of dead roots (from the removed trees) that the beetle larvae feed on. Could be the males like to hang out in sunny areas near a shrub (the holly in my yard in place of the Baccharis as reported on the web) waiting for the females.
Again, thanks! Steve Hartman
WE are very excited to receive your new photos of the female Scarab Hunter Wasp, but the resolution on the original images you sent was much higher.