Silhouette Dropwing (Trithemis hecate)

The photo above (by Greg Darling) can be viewed in OdonataMAP here.

Find the Silhouette Dropwing in the FBIS database (Freshwater Biodiversity Information System) here.

Family Libellulidae

Trithemis hecate SILHOUETTE DROPWING

Ris, 1912

Identification

Small size

Length up to 43mm; Wingspan attains 68mm.

A slender, dark blue species. The thin abdomen easily differentiates it from other dark blue dropwings like Trithemis furva (Navy Dropwing) and Trithemis dorsalis (Highland Dropwing). Closest to Trithemis aconita (Halfshade Dropwing) in appearance. Both species have slender abdomens but are easily told apart by their very different habitat choices.

Additionally, Trithemis hecate is the only dark blue dropwing in the region with pale pterostigmas.

Females are easily confused with other Trithemis species. They are best identified by their association with the males.

Click here for more details on identification of the Silhouette Dropwing.

Trithemis hecate – Male
Linyanti, Botswana
Photo by Ryan Tippett

Habitat

Its natural habitats are subtropical and tropical pans, floodplains and marshes. It prefers standing or still water with emergent plant growth of reeds, grass or sedges. Frequently found perched on trees and bushes a short distance from the water, especially during the hottest time of the day.

Habitat – Near Kosi By, KwaZulu-Natal
Photo by Ryan Tippett

Behaviour

Males perch on emergent stems, often far from the shore, on the last reeds before the open water starts. From this position they often appear all dark and silhouetted, hence the common name. Females are found on trees and bushes surrounding the wetlands, often some distance from the water.

Status and Conservation

In South Africa, Trithemis hecate is scarce and erratic in occurence but can be abundant at sites further north, such as the Okavango Delta in Botswana. It is listed as of Least Concern in the IUCN Red List of Threatened Species. This species is found mostly in pristine habitat and is fairly sensitive to habitat degradation.

Distribution

Wide spread in tropical and subtropical Africa. It has been recorded in Botswana, Chad, the Democratic Republic of the Congo, Gambia, Guinea, Kenya, Liberia, Malawi, Mozambique, Namibia, Senegal, South Africa, Tanzania, Uganda, Zambia, Zimbabwe, and possibly Burundi. It also occurs on Madagascar.

Below is a map showing the distribution of records for Silhouette Dropwing in the OdonataMAP database as at February 2020.

The next map below is an imputed map, produced by an interpolation algorithm, which attempts to generate a full distribution map from the partial information in the map above. This map will be improved by the submission of records to the OdonataMAP section of the Virtual Museum.

Ultimately, we will produce a series of maps for all the odonata species in the region. The current algorithm is a new algorithm. The objective is mainly to produce “smoothed” maps that could go into a field guide for odonata. This basic version of the algorithm (as mapped above) does not make use of “explanatory variables” (e.g. altitude, terrain roughness, presence of freshwater — we will be producing maps that take these variables into account soon). Currently, it only makes use of the OdonataMAP records for the species being mapped, as well as all the other records of all other species. The basic maps are “optimistic” and will generally show ranges to be larger than what they probably are.

These maps use the data in the OdonataMAP section of the Virtual Museum, and also the database assembled by the previous JRS funded project, which was led by Professor Michael Samways and Dr KD Dijkstra.

Further Resources

Virtual Museum (OdonataMAP > Search VM > By Scientific or Common Name)

More common names: Skraalvalvlerkie (Afrikaans)

Type Locality: Tananarive, Madagascar

Recommended citation format: Loftie Eaton. M; Hofmeyr S; Tippett RM; Underhill L. Silhouette Dropwing Trithenis hecate. Biodiversity and Development Institute. Available online at http://thebdi.org/2020/04/29/silhouette-dropwing-trithemis-hecate/

Dragonfly Atlas: Megan Loftie-Eaton, Sally Hofmeyr, Ryan Tippett & Les Underhill
Dragonfly Atlas: Megan Loftie-Eaton, Sally Hofmeyr, Ryan Tippett & Les Underhill
Megan Loftie-Eaton is our communications, social media and citizen science coordinator. Prior to her work for the BDI, she coordinated OdonataMAP, the Atlas of African Odonata. Sally Hofmeyr has many years' experience in the academic world, writing her own material and editing the work of others. Her academic background is in the natural sciences: her PhD and first postdoc in ornithology and environmental change (Animal Demography Unit, University of Cape Town). Ryan Tippett is an enthusiastic contributor to Citizen Science and has added many important and interesting records of fauna and flora. He has been a member of the VMU since 2014 and has currently submitted over 11000 records. He is also on the expert identification panel for the Odonata Map project. Prof Les Underhill has been Director of the Animal Demography Unit (ADU) at the University of Cape Town since it started in 1991. Although citizen science in biology is Les’s passion, his academic background is in mathematical statistics.