STELLENBOSCH University (SU) researchers have found that the Overberg dragonfly is the only known insect to experience “remarkably fast” temperature-induced colour change in both sexes.
The Spesbona damselfly is one of the few “chameleons” of the dragonfly world and quite unique to the insect world.
Both the male and female of this endangered fynbos species change from royal blue to a much darker brown within seconds when temperatures drop, when a cloud passes over, or when the sun sets. When temperatures rise again, the insect again rapidly returns to its former blue glory.
“It is the only insect species so far known to science in which this reversible colour change – due to temperature changes – is present in both sexes, says SU conservation ecology postgraduate student Charl Deacon and his supervisor, insect conservationist Professor Michael Samways.
They set out their findings in an article in the Journal of Insect Conservation.
Being able to change colour is an ability that the Spesbona damselfly (Spesbona angusta) shares with only a handful of other dragonflies, but they are the only ones in the world which can reversibly switch their colour scheme back and forth in both sexes.
This smallish-sized type of dragonfly was first discovered in 1920, when a female specimen was first noted in a section of the Cederberg mountains near Ceres.
It was then thought to have become extinct, but was sighted again some 82 years later in a marshy patch in the Theewaterskloof conservancy area between Villiersdorp and Franschhoek.
Its rediscovery by Samways and photographer Warwick Tarboton followed the clearing of invasive alien trees from the area.
It is still the only known location of this endemic South African species, which is listed as endangered on the International Union for Conservation of Nature (IUCN) red list. It lives in still pools or streams lined with water weeds, bushy fynbos and overhanging plants.
Samways first noticed its colour-changing ability in 2014 during a field expedition looking for dragonflies. At the time, Deacon was still an undergraduate student and took on the task of finding out more about how this process works, and to find out more about the damselfly.
“When Samways initially told me about this phenomenon, I thought that an insect capable of reversible colour change would be a very neat topic to investigate – especially since Spesbona angusta is an endemic species,” remembers Deacon, a budding young researcher who has been studying water-related matters since his school days in the Northern Cape mining town of Kathu.
“Seeing the colour change happening right in front of my own eyes within a few seconds is simply amazing, and reminded me how much I adore insects,” adds this MSc student in entomology.
“After reading a few publications on colour change in invertebrates, we formed our methods and started the first round of experimentation,” Deacon remembers.
Because the dragonfly is so scarce, the researchers only collected two males and two females from the area. Along with water and plant samples from the native area, the insects were taken back to Stellenbosch University, where a terrarium was built to mimic their natural environment under laboratory conditions.
They then waited to see what happened when temperatures in the terrarium were adjusted.
They observed rapid and clear changes, not only in the colours observed, but also in the richness of the hues.
“The shortest colour change occurred within 16 seconds, and the longest was 32 seconds,” says Deacon, who describes it as “remarkably fast”.
In the so-called “cool” state, with temperatures ranging from 18ºC-21ºC, most of the insects’ features were brown.
In the “intermediate” state (22ºC-25ºC) these features were a mixture of brown and purple, while these were either violet or royal blue in the “warm” state (26ºC-28ºC).
The researchers speculate that this colour change is part of the insect’s strategy to adapt to temperature changes, and also to increase their chances of attracting the best possible mates.
The insect is not found within a nature reserve that is formally protected.
“This species is so habitat specific and also does not tolerate any changes to it,” says Samways.
“If we want to ensure the existence of this phenomenon in nature, every effort must be made to maintain its habitat as intact as possible and to continue removing alien plants from the area.”
Facts about Spesbona Angusta, formerly known as the Ceres streamjack, the Ceres featherlegs or the Ceres stream-damselfly:
l It matures from a very unusual larva, easily distinguished from any other South African dragonfly larva.
l It is a slender, dark blue and black damselfly with strikingly long, curved appendages.
l Its “normal” colour is royal blue on sunny days, when dragonflies are most active.
l Its face is greyish blue and black, while its head is bright greyish blue. The head also has a distinct matt black, horn-shaped marking when viewed from above.
l Its wings are clear.
l Small black markings appear on the last few segments (the “tail end”) of its body.
l Duvenage is from the communications department at SU