From Garden Insects of North America by Whitney Cranshaw "Slugs and snails are types of animals known as gastropods, fairly close relatives of clams, mussels, and other mollusks. As such they have several different features than the arthropods (insects, mites, spiders, etc.) and lack distinct segmentation or an external skeleton. The body is soft and moves by means of a broad, muscular "foot" that covers the underside. On slugs a large lobe called the mantle is present on the front half of the back; this is covered by a hard shell in snails. Two pairs of tentacles are present in the front, a short pair for sensing odors and a longer pair tipped with eyes. Many slugs and snails are hermaphrodites, possessing both sex organs, but these mature at different times producing male and female phases."

From Field Guide to the Slug by David Gordon
During courtship, two slugs will circle each other, often for hours, with both partners engaged in ritualized bouts of lunging, nipping, and sideswiping with their tails. Two slugs may also display their disproportionately large sex organs. The great gray garden slugs penis is nearly half its total body length. In fact, penis size is reflected in the scientific name of one banana slug species: dolichophallus Latin for "long penis"

WARNING DO NOT READ IF YOU ARE EATING
Having two outdoor cats have definitely made a huge dent in my rodent population but the down side is these gifts (either whole or regurgitated) litter my entryway. Much to my surprise as I always believed slugs were vegetarians I observed eight slugs feeding on the remnants of a kitty gift. I have also come to learn that slugs will eat other slugs of different species.

The lifespan of a snail varies from species to species but averages somewhere between two to seven years. With that in mind I suppose that trying to decrease the population could be done during spring, summer, or fall.

Game Plan
1. Trial a variety of slug traps, ie water bottle top cut off just below the neck then stuck inside the bottle and tapped closed, cottage cheese container with lid cut openings on sides just below the lid.
2. Trial trap bait of beer (con needs to be fresh to be effective and cost) or the lesser expensive 2 tablespoons of flour, one teaspoon of brewers yeast, and one teaspoon of sugar mixed into two cups of warm water.
3. Buy large amounts of Sluggo at 50% off nursery sale.
4. Evening hand picking. Hmmm on second thought I might skip this one.

So I thought I would share with you overtime my Operation Snail/Slug Saughter with the hope that you might share your experiences with these pesky gastropods. Keep in mind that I have allowed this population to multiply to a point that I would consider the situation to be extreme. Another words a couple of pie plates of beer wont even begin to make a dent.

Since you have kitties, Escar-Go! Slug & Snail Control is a slug bait made by Gardens Alive which is pet-safe. Don't know if that is the case with Sluggo since I do know that some slug baits aren't safe around small kids and animals. There are probably other pet-safe slug baits - this is the only one I know about.

I have heard that crushed eggshells around particularly vulnerable plants is supposed to help keep out softbodied critters, but in my experience the birds remove the eggshells faster than I can eat eggs so I don't know if it actually works.

This year I also started sprinkling my slug killer a day or two before I planted out my seedlings. Kinda of a preventative measure type of thing - get rid of the slugs before I planted the slug food. The stuff I have is little white pellets, and I just keep inspecting the ground - if I don't see the pellets, I sprinkle more.

Of course, that was before I knew about slugs' amazing reproductive apparatus, described in your post; emptying trays of beer full of slimy bodies might be more fun, now that I'd know I was looking at something awesome.

Those snails being modeled on your young friend are the biggest things I've seen since living in the SF Bay area. Yuck!