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TaxonomyBrowseInfoImagesLinksBooksData
Photo#1122594
Mydas from the lower Colorado River - Mydas ventralis

Mydas from the lower Colorado River - Mydas ventralis
Across the Colorado River from Needles, and a few miles south, Mohave County, Arizona, USA
August 3, 2015
This was the first of several of these mydids encountered perched on stems of the shrub Pluchea sericea, growing on the levee above the Colorado River. This one was by itself, but the second group (found about 45 minutes later) consisted of about 6 individuals...at least one of which was a mating pair...all perched near each other about 6' above the ground.

   

This keyed to genus Mydas in the MND(1). Going through the online key to Mydini at Torsten Dikow's web site led to M. ventralis. That's what I had expected, based on browsing BugGuide and other images on the web and comparing with the MCZ type of M. rufiventris and the description of M. abdominalis, both of which are synonyms of M. ventralis. I'd also like to run this through the 1926 revision of Mydidae by C. W. Johnson, but haven't yet been able to access that reference.

In order to get to M. ventralis in Torsten's online key, one needs to have "alula black", which can seen to be the case in the 2nd image of the series here. But in at least one of the (otherwise similar looking) individuals seen in this population the alula appears completely hyaline. I presume this is simply variation which doesn't "respect the key" (as often seems to happen in taxonomy, despite a key writer's best efforts).

These seem to me like they may be mimics of the scoliid wasp Triscolia ardens:

   


QUESTION FOR COGNOSCENTI: Is there a simple way to tell whether this is a male or female? (For example, from the available view of the terminalia?)

Images of this individual: tag all
Mydas from the lower Colorado River - Mydas ventralis Mydas from the lower Colorado River - Mydas ventralis

Female
The simple answer is that is not very easy to tell, without clear views, like yours. Also, the abdomen may be tipped with black or without black color in this species, probably in both genders. I'm not exactly sure of this variable character.

♀ = The females have a small and short projection, tipped with a few hairs, that extends out, near the top-side or dorsal edge, along the mid-line of the abdomen. The terminal segments are always very close to parallel with the previous one, including the small projection.
♂ = The males have larger parts, wider on the lateral edges and lacking near the center-line, often with visible hooks or spines and with much long hairs, distributed evenly. The tip usually appears to be angled upwards, often more than 10deg. from the previous segment.
These other images, (below) might help you to see. Both of them are some other species, but consistent with most species in the genus. (similar to other families in Asiloidea)
You shouldn't need me to comment on every image, but please let me know if you need anything. The pinned specimens may have a few visible parts on them, that might provide more answers for your question.

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