20 August 2005

Helicopter Damselfies

Dragonflies of the World by Jill Silsby is ode porn. Not only is it full of great information on odonata biology, it offers a tantalizing overview of the world's odonata. From the time I first looked through its pages, many families and species quickly ascended to the top of my "must see" list. One such family was the Pseudostigmatidae, or Forest Giants. The largest living odonate in the world, Megaloprepus caerulatus (wingspan of about 7 inches) is in this family, which is found in Latin American rainforests. Despite their size, pseudostigmatids are rather delicate looking, sort of like extremely elongated spreadwings (Lestes).

Another common name for this group is helicopter damselflies. Pseudostigmatids have very large spots at their wing tips, sometimes replacing the pterostigmas. When they fly -- quite slowly -- they really resemble helicopters! They also have a very specialized mode of foraging: they hover in front of spiderwebs and pluck out the spiders, preferring soft-bodied arachnids to hard-bodied ones. Although they look ungainly, they are skillful at manuevering close to the web to grab the spider, and then going in reverse to back away without getting entanged in the web.

This female (left) is in the genus Pseudostigma; according to a checklist by T.W. Donnelly it should be P. accedens. The other species is P. aberrans, a good match for this photo. A key to the Costa Rican species notes that accedens is rarely found in Panama, so it's a toss-up. This photo was taken at the Metropolitan Nature Park in Panama City. UPDATE: Both Donnelly and Dennis Paulson have identified this as most likely Mecistogaster ornata.

Pseudostigmatidae breed in standing water in tree holes. Males will defend good breeding sites. Little sunny openings at stream crossings are also good places for spiders. Consequently, we were able to find Megaloprepus caerulatus in many such locations. Although the largest odonate in the world, individuals vary greatly in size. Some seemed truly huge, others, just big.

The one on the right allowed us to take many photos as he explored leaf tips looking for spiders. The second photo, below, isn't great, but shows that the black spot on the wings is actually metallic blue. When they land, helicopter damsels fold their wings slowly, it looks really cool! This individual was photographed outside of Gamboa, Panama, along the Rio Chico Masambi.



A web site on the odonata of La Selva, in Costa Rica, has photos of specimens of four species of helicopter damselflies. Seeing these magnificent damselflies was one of the highlights of my trip. They are still at the top of my "must see" list!

7 comments:

Mark said...

Nicely presented and good photos, girl!

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Anonymous said...

amazing! thanks!