Tuesday, June 20, 2017

Species Spotlight: Four-spotted Skimmer

We saw our first Four-spotted Skimmers of the year a few days ago at Cranberry Lake. Curiously, we have never seen one at Heart Lake, even though it is only a few miles away and is very similar to Cranberry Lake. Eight-spotted Skimmers haven't been seen yet.

Heart Lake and Cranberry Lake are very similar, but have distinctly different dragonfly populations.

Here's a male Four-spotted Skimmer:

Four-spotted Skimmer, male.  Notice the dark spots at the nodus (center of leading edge) that give this dragonfly its name.  The dark spots near the wing tips (the stigma) don't count, since all dragonflies have them.  Also, note how the front two legs are folded up and tucked behind the head, just as they are in flight.

Males and females are practically identical in this species. The best way to distinguish them is by behavior—males patrol the shoreline looking for mates; females perch on vegetation when not dipping the tip of their abdomens in the water to lay eggs—and by the presence (males) or absence (females) of hamules under segment 2 of the abdomen.

Here's a female Four-spotted Skimmer, showing the lack of hamules, and the presence of a small egg scoop:

Here's a male Four-spotted Skimmer, clearly showing the hamules under segment 2 of the abdomen:

The hamules are like latches that hold the abdomen of the males and females together in the wheel position.

Four-spotted Skimmers have a high perching index (about 80 – 90%), and hence are easy to observe and photograph.  If you see a golden brown dragonfly in our area it's almost certainly a Four-spotted Skimmer, so the ID is fairly easy as well.

Mating is a rapid affair with these dragonflies.  Their short, pudgy abdomens aren't particularly flexible, and hence they stay in the wheel position for only about 10 to 15 seconds.  After mating, the female dips the tip of her abdomen repeatedly into the water to lay eggs while the male hovers above for protection.  They don't stay attached in tandem during egg laying, as do many meadowhawks, because their inflexible abdomens aren't well suited for that kind of maneuver.

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