Enallagma praevarum
photo (above & next 2 below) 7 Oct 2006
Carmel River at Garland Ranch Regional Park
Arroyo Bluet is one of the blue-and-black bluets in Monterey County (or at least the males are blue-and-black; females are tan-and-black but none are shown on this page). But males do separate into two groups if one focuses on the middle abdominal segments — numbers 3, 4, and 5. In MTY there are only two species — Arroyo and Tule — whose segments are more black than blue. Segment 3 is variable but 4 and 5 and definitely more black than blue. All other MTY bluets (and most other California bluets to boot) have these segments decidedly more blue than black.

Separating Arroyo from Tule Bluet is not easy, but they have different habitats. Arroyo Bluet is an ode of running water — streams, rivers, rivulets — while Tule Bluet is typically an ode of open marsh or pond edge. However, rather little information has been collected on either species in MTY, and their comparative distribution is not yet known. The two specimens from the county are from the Salinas and Arroyo Seco rivers. The latter is the only spot at which Tule Bluet has also been confirmed to be present with Arroyo Bluet (but probably in quite different habitat).

If one nets the male bluet and examines it with a 10x lens — or can view the appendages at close range through digital photography (left) — Arroyo Bluet is identified by its distinctive two-pronged cerci. In this view (left) the pair of cerci can be seen side-by-side. We have a good view of the left-hand set nearest to us, but can see part of the right-hand set also. Looking at the near set of appendanges, distinguish between the lower pale hook (the paraproct) and the black upper appendange (the cerci). Note that the upper appendage is forked with a long upper fork and a comparatively short and pointed lower fork. To me this looks like an old-fashioned can-opener. This can-opener shape identifies a male Arroyo Bluet, as it is quite different from Tule. However, River Bluet E. anna, which occurs in eastern California, also has a two-pronged cerci and is much more similar to Arroyo Bluet in this feature. River Bluet, though, has more blue than black in the middle abdominal segments. [Females have different appendages and female Arroyo probably cannot be identified from other bluets in the field; Manolis 2003].

Arroyo Bluet is not yet well surveyed in MTY. The confirmed records are all from creeks and rivers with good currents: Carmel, Salinas, and Arroyo Seco rivers, and Piney Creek. Reports from Laguna Grande in Seaside need further verification. Some of the habitats have been heavily wooded (e.g., Carmel River) but others are more open (e.g., Salinas River south of San Ardo).

Dates range from 18 April to 7 October. This is very close to the flight dates known from the State (March-October; Manolis 2003).

Literature cited:
  • Manolis, T. 2003. Dragonflies and Damselflies of California. Univ. of Calif. Press, Berkeley.
Web resources:
Major identification web sites with much information on California odes include: For sites with excellent photos to compare for identification or to simply enjoy, see: Many of these sites have links to other useful pages. Kathy Biggs's site is particularly useful in her selection of links.

All photos © Don Roberson 2007


Page created 11 Feb 2007