Thora Whitehead's poetic plea for enlightenment about slugs demands a response. So, here are some thoughts, verse-by-verse.
The beginning of this poem reminded me of a comment by the late Stella Davies, then suffering from trouble in her ageing joints. She told me she would love to be a slug: not a snail, a slug. Why? Slugs have no skeleton and never a need for hip replacement. Without a shell they can change shape and move through very small gaps. You cannot love a slug more than to wish to be one.
How do slugs grow? Generally at a remarkably unsluggish pace. Put some hatchling slugs in a jar with a loose fitting lid, a damp substrate and a supply of food – fungus, carrot or other vegetable scraps will do for most species. Watch and wait. Growth can be very rapid. Generally they grow by increase in size without any accompanying change of shape (not that shape is very easily definable in creatures that lack any rigid structure). It is worth noting that it is difficult to quantify precisely the size of a slug. Length varies according to posture; mass and volume can vary considerably with water content.
What do they eat? Again, watch them in the wild and in captivity.
Some do attack garden flowers and food crops. Most individual slugs may be pests but most species (in the UK, at least) are not major pests. Compare species compositions in the vegetable garden, the flower garden and the compost heap. Try feeding captive slugs with different foods (including fresh vegetation, decaying vegetation, fungus, lichen, algae, decaying animal matter, animal droppings). Just be careful not to mix Limax maximus with slugs of any other species (except when investigating its diet).
Anatomy? Here is a diagram of a general purpose slug – not all slugs have all the features labelled:
Most slug species do not have the lateral symmetry that we normally expect in an animal; this is because they have evolved from snails with coiled shells – a clear case where lateral symmetry is impossible. You may just be able to see the vestigial shell in some species – under the skin, opposite the pneumostome.
Not romantic? At one extreme, Arion ater shows an extreme reluctance to indulge in any sexual machinations with other individuals – being a hermaphrodite does help perpetuate such an antisocial species. Several species do have long courtship rituals, often involving moving in ever-decreasing circles, possibly following a sexually attractive scent trail, until they meet for copulation. Tandonia budapestensis is reputed to remain in a copulatory embrace for up to 18 hours. I have not had the patience to watch this for more than about 18 seconds, so cannot confirm it directly. But 18 hours? Can you really call that unromantic?
Is it necessary to have them in captivity to study them? Not absolutely. Individuals of some species, such as Limacus flavus and Limax maximus, can be identified individually by their markings – keep a library of digital images to allow you recognise them. Limacus flavus has strong homing instincts and often associates closely with human habitation. It is an ideal subject for study. Find which stone it roosts under and, thereafter, follow its perambulations night after night.
How interesting are they? Certainly they may not be as strikingly attractive as a brimstone butterfly, nor sing like a nightingale but they are under-studied and have ecology and behaviour very different from many other species. There are many simple questions which can excite the imagination. Why does the tree slug, Lehmannia marginata, have to climb to the tops of trees to feed even though it requires taking on a heavy water load to compensate for evaporation and slime-trail production? Why is the mucus of Arion subfuscus non-sticky and makes human skin feel rejuvenated when it is rubbed in? Does Arion ater prefer dog droppings to Hostas? Are the little mites which scurry over the surface of larger slugs parasitic, symbiotic or mutualistic?
I was once told that you do not judge great works of art; instead they judge you by your reaction to them. Being a philistine, I would not know about art. However, replace 'great works of art' by 'slugs' and I know you have the truth.