Many green spiders - appearing alive and well - are visible. However, all have been paralysed and are unable to move, even though they remain alive.

This is one of nature's more macabre stories, played out every summer in the Ballarat district.

A female wasp searches the ground and vegetation for a spider, and, on finding one, she stings it, resulting in the spider's permanent paralysis.

The flying wasp is usually agile enough to avoid being caught by the spider she's hunting. The wasp carries or drags the victim to its previously prepared nest, where she lays an egg on the spider's abdomen. The cell or section with the spider is then sealed by the wasp so it is protected from predation. In this case, mud has been used to make the wall and cells.

Most spider-hunting wasps provide just one spider to supply their larvae with sufficient food for all their growth and development, but some species provide more than one.

The egg hatches and the young wasp grub starts feeding on its spider host, which is alive but paralysed.

The wasp larva saves the vital organs - heart and central nervous system - until last. This prevents the spider decaying before the wasp larva has fully developed. Eventually, the larva pupates and emerges as a winged wasp.

These are not social wasps like European wasps - just one female makes the nest and undertakes all the work.

They are native wasps. A wide range of spiders is taken by wasps, but different wasp species have their own spider preferences. Also, an individual wasp tends to have its preference of just a few sorts of spiders. This is clearly the case in the accompanying photo, where green spiders have been selected.

These appear to be small specimens of a type of green huntsman, but they may be flower spiders, or perhaps both. There is considerable variation in size.

In studies of some other wasps, it has been found that the larger the body of the host the larger the wasp that emerges.

January orchid reports have included sharp midge orchid, austral ladies' tresses and two sorts of hyacinth orchids.

The hyacinth orchids have been reported from the Beaufort and Creswick forests, with the sharp midge orchids also near Beaufort.

Austral ladies' tresses orchids (Spiranthes) are flowering near Creswick.

This uncommon plant has also been recently seen at Spargo Creek and Pootilla.

Can you identify this flower growing in the crater walk at Mt Buninyong?

C.V., via email.

This purple-flowered plant is called self-heal, an Old-English name for this introduced plant that was once considered to be a cure-all for almost every sort of disease.

It is a low-growing perennial plant, seldom noticed until its flowers appear in summer.

It prefers damper or higher-rainfall places, often shady or partly shady.

Although it is in the mint family, it does not have aromatic leaves.

Like mint, it has a strong root system that creeps along underground.

The name suggests that some sort of healing properties are associated with this plant.

These are still published from time to time, but the plant is not widely used in 21st century herbalism.

Self-heal is native to Europe, and is now a widespread and common weed in Victoria, including the Ballarat district.