​I am amazed at how little I know about the natural world when I delve into what I often think is a simple subject
Like many people, I thought that mealybugs are powdery and scales waxy and didn't know much about psyllids at all. Not so!
Psyllids are commonly seen in lerps (oyster shaped shell of dried honeydew) and in galls. When exposed, the adult females look like a tiny wingless cicada.
Mealybugs and scales are sucking insects (like aphids) that secrete a layer on their body to protect themselves and are immobile or slow moving. They are all slow moving or stationary sucking insects, that excrete honey dew from their anus. Ants attracted to the honeydew harvest this and protect them from predators. (This brings a whole new aspect to the saying "kiss my __"  enough said). Excess honeydew secretions that drip down the branch are used by moulds to create a black sooty stain that can be seen on the stem and the ground below the shrub.
What we see on plants are almost all female. The adult male looks like a tiny wasp and only exists to mate. I have met some humans like that but they eat, and also live much longer. Some scales have dispensed with males entirely and produce clones of themselves (parthogenesis). Some reproduce via eggs, others by live birth, to produce mobile young called crawlers. Once it finds a nice spot a crawler develops a coat or 'shell', and some dispense with legs and antennae.
There are few easy rules of thumb to distinguish between them.  This article may help.
Mealybugs are flat, oval in shape, and have a powdery coat. They prefer moist warm conditions and are not found in the wheatbelt, where we only find scales.
 Scales are very diverse. A few  form galls on eucalypts, some look like mealy bugs, some look like "typical" waxy scales, but many have a cottony exterior and strange shapes. Here are three categories:-

Cottony scales from the ancient Margarodidae and Monophlebidae families are the most common type in Foxes Lair.These have a cottony coat and/or weird  cottony appendages. The one below that I found on a marri twig was surprisingly colourful with dinky little legs.

Greetings fellow Foxies,
Wolwolling pool is a remarkable pool in the main bed of the Arthur River south of Highbury. In her book “Wolwolling Reflections” on the history of Highbury, Gwen Warren writes that the pool was a favoured camping place for indigenous Australians and was one of only 2 permanent freshwater pools around Highbury for shepherds, who with sandalwood cutters were the first white settlers there. Wolwolling is an aboriginal name meaning ‘Weeping women’ because scores of aborigines died from a catastrophic measles epidemic after contact with Europeans, and were buried near the pool. Wolwolling was also the original railway siding before becoming the Highbury township.
The general direction of the Arthur River has changed little over millions of year.  It was once was the headwaters of the Collie River before land movement caused it to be diverted then captured by the Blackwood near Towerinning Lake. The Arthur rRver then  became relatively sluggish with an extensive broad valley system.
In another Foxypress I explain how lakes form and much of these flats and associated lakes have become saline. Vegetation surrounding the pool itself is still fairly healthy with York gum and salt sheoak trees, Needlebush (Hakea preissii) and unfortunately lots of weeds.
The image below shows a view of the pool (see arrow) looking east. The pool is located where the river has cut around a roughly east/west trending upland that has caused the river to become faster and deeper. I suspect that the rock under the upland is a line of dolerite (black rock), that has weathered to form York gum red clay. This can block or redirect groundwater that may form a spring.

To get to Wolwolling Pool, turn east off the Great Southern Highway onto Wiese Road south of Highbury, drive over the railway crossing and the sharp right then left turns and stop or turn left just before the river crosses the road. The first and second tracks to the left join just before a large boggy patch. Park here and walk in about 200 metres. Driving is not recommended as the track in can be wet in winter and is almost impassable in 2 spots.
Please don't camp here as the place is already suffering from unmanaged 4-WD vehicle traffic and mosquitos are likely to be thick in the evening. 
One can also launch a canoe at the crossing for a pleasant 400 metre paddle in the growing season.
Morning is the best time to visit.

The pool was a popular swimming place before the days of swiiming pools, reticulated water and amoebic meningitis warnings. 
It was very pleasant there this July after good rain. The water slowly flowing into the tree lined pool was clear and brackish with water weed for the ducks. Great bird watching place, lots of bird song and sooo peaceful.
Lake surrounds contain the succulent samphire that is seen on salt land but rain washes salt out of the topsoil, and soil between red to green samphire plants is densely coated in bright green water-loving Cotula (Billy button) plants that will produce a carpet of yellow flowers in spring. Later I saw a pair of black swans with cygnets.