The first day of issue was 19 APR 1982. There are 2 covers for this set from the 1982 Fleetwood ‘Flora & Fauna’ release:
“Litoria citropa – Blue Mountains Tree Frog – The great island continent of Australia was cut off from the rest of the world for millions of years. During this time, an array of exotic and interesting animal species developed there. Many of these are extraordinary crea- tures found nowhere else but in this vast, southern nation. Australia recently honored several of these animals on a series of colorful stamps. One of these stamps, featuring the Blue Mountains Tree Frog, ap- pears on this First Day Cover. The Blue Mountains Tree Frog is well adapted to his forest home in New South Wales and Eastern Victoria He bears special pads on his appendages which enable him to climb about nimbly amid the trees. However, unlike many Tree Frogs from other parts of the world, the Blue Mountains Tree Frog can Often be observed on the ground, When found there, the Frog is Often near water, sunning himself in the warm sand or mud along the shoreline of a marsh or lake, This is the ideal spot for the Tree for like the spiders Frog to hunt his favorite food Tree Frog, the spider enjoys the cool, moist mud near a lake, This amphibian is easily recognized by his distinctive coloration and triangular head shape. Also, like many amphibians, the Blue Mountains Tree Frog bears very prominent eyes which can be alarming if a hiker cornes upon the Frog unexpectedly. Whether sunning himself beside a lake or climbing about in the branches of a tree, the Blue Mountains Tree Frog is one of Australia’s most interesting amphibians.”
“Yellow-faced Whip Snake — Demansia reticulata – The long, thin creature featured in the stamp and original art on this First Day Cover is native to a large part of the Australian continent. In fact, he is well-known in most of Western Australia and adjacent parts of the Northern Territory and South Australia The one place in Australia that hikers can be quite certain they will not meet a Yellow-faced Whip Snake is in Australia’s sandy desert areas for this Whip Snake prefers a less hostile environrnent. The snake derives his narne from his distinctive Whip Snake coloration. Across the animal’s face from nostril to nostril there is a dark band edged in yellow. This creature Of the Australian countryside may be found in several different from steel grey to green. Some individuals bear colors reddish tinges on their scales. But, despite the many different colors, all are variations of one species of snake. These snakes are among the most interesting reptiles of Australia. However, they can also be among the most dangerous to study for their bite is venomous and they are fast-moving, Many people believe that the Whip Snake attacks by constricting first, like a rattlesnake does. This is not true. The swift-moving Yellow-faced Whip Snake can strike suddenly and without much warning. These long, thin creatures are indeed named appropriately for they look very much like a whip as they slither rapidly through the grass. Few people keep the Yellow-faced Whip Snake as a pet for Whip Snakes never tame well enough to make good house companions. They are creatures of the wild and with their swift movements and venomous bite, they plan to stay that way. “
There are variations of these covers (with & without printed text on the back of the envelopes). Curious ! Also I own the original black & white Gene Jarvis cachet design artwork for both these covers.
Here is some information from the Unicover website about Gene Jarvis: