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Slugs

Slugs Mating

Monday’s post stated that the nature of the activity the slugs were engaged in was undetermined.  Since then it has come to my attention that had I been truly “naturally curious” and popped the bubble of slime, I would have had the rare opportunity of seeing two entwined slug penises.  Here is a descriptive quote describing slug reproduction.

Like all slugs, those in the genus Arion are hermaphrodites (possessing both male and female sex organs). They can reproduce either by self- or cross-fertilization, depending upon conditions and habitat stability. When two slugs mate with each other, they each simultaneously play the role of both sexes, exchanging sperm with their male genitalia. At times, the male sex organs of two slugs become entangled during mating and the slugs may bite them off in order to free themselves, a not uncommon sacrifice known as ‘apophallation.’ From then onward, the apophallated slugs are only able to reproduce as females. Arion subfuscus mates in the mid-to-late summer. Several days after mating, slugs will lay hundreds of 3-4 mm eggs in the soil, and die shortly thereafter. Although there is no parental care in this species, the eggs are imbued with a caustive agent called miriamin that serves in a large part to protect them from predation. In around a month, the juveniles hatch as small, pale-brown versions of their adult selves. They typically take at least 4-6 months to achieve sexual maturity, mating and dying themselves before the new generation hatches from the eggs.” (https://www.projectnoah.org/spottings/1952620518)


Slug Slime

Most of us who have encountered slugs know that if you handle one, the slime it produces on the lower surface of its body persists on your hands even when you wash them with soap and water. (If you let the slime dry and rub your hands together, it will come off in small beads.)  Slug slime contains water, mucus and salts. It keeps a slug’s skin moist, preventing it from drying out, and aids in locomotion.

Slug slime changes as the slug moves. Initially it has the consistency of a liquid gel.  It is solid at rest and turns to liquid under pressure.  A slug sticks part of its body to the ground with its slime, uses its muscles to move its body forward, and then pulls its body away from where it was stuck. More slime is released and the process is repeated.  It’s interesting to note that slugs are strong enough to move without the aid of slime, but nonetheless are always producing it.

Slug slime has its good and bad points. Scientists are studying slug slime properties in their search for a better surgical adhesive. Most substances are either flexible or sticky, not both, like slime.  On the other hand, there are some aspects of slug slime that are not all that appealing.  In addition to being next to impossible to remove from your hands, slug slime can carry rat lungworm (Angiostrongylus cantonensis), a parasitic roundworm that mainly lives in rodents such as rats and can infect slugs (and snails) that come into contact with infected rodent feces.  This disease can cause a form of meningitis which is prevalent in Southeast Asia and tropical Pacific islands.

(Photo:  Two slugs & bubble of slime. Nature of activity not determined! Thanks to Alice Trageser and Mary Landon for photo opportunity.)

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A Gardener’s Favorite Beetle

bronze carabid 161Ground beetles (family Carabidae) are fast moving beetles, many of which are predators with specialized diets.  One ground beetle (Cychrus caraboides) eats only snails (its head and thorax are very slender, allowing access to the inside of a snail’s shell).  Another, Harpalus rufipes, limits its diet to strawberry seeds.  Loricera pilicornis uses bristles on its antennae to trap springtails and mites.

The Bronze Carabid, Carabus nemoralis, (pictured) uses its large curved mandibles to crush and slice through prey – it will eat or try to eat just about any invertebrate, but specializes in capturing and eating slugs. Its hardened forewings, or elytra, have a coppery sheen to them, and parts of its thorax and the edges of its elytra are iridescent purple. This nocturnal, introduced, flightless, one-inch-long beetle resides throughout the Northeast and is already actively pursuing slugs.

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Slug Scat

slug & scat 066Slugs produce lots of mucus – some covers their whole body and makes it difficult for them to be picked up by a predator, some forms a “slime trail” that aids them when they are moving, and some envelopes their waste. After a slug has eaten and digested food (a wide variety of plants, fungi, earthworms and carrion), a mucus string of scat leaves through its anus, which is hidden under the leathery patch called a mantle, located just behind its head. The odd position of this opening is a result of the slugs’ evolutionary descent from snails. In a snail this opening must be outside the shell, and thus is far forward on its body. (Congratulations to Jean and Michele for their spot-on guesses.)

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Common Gartersnakes Giving Birth

8-15-14  common gartersnake 082Common Gartersnakes mate soon after emerging from hibernation in the spring, in March or April, and four months later the females give birth to live young. The newborn snakes are 5 to 9 inches long at birth and from day one have to fend for themselves. Their diet at this early stage consists of earthworms, insects, slugs, tadpoles, small frogs and fish. If there is an abundant supply of food, the young snakes can grow as much as 1 ½ inches a month during their first year. Earthworms are their preferred diet and gartersnakes are known for their ability to find them, even underground. It turns out that earthworms produce a chemical substance in their skin that is easily detected by (and attractive to) Common Gartersnakes. (Thanks to Eli Holland, who located the worm-eating newborn Common Gartersnake in the photograph.)

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Where Do Slugs Spend the Winter?

4-1-14  slug under bark 223Slugs mate and lay eggs in the spring and fall, and can live 12 to 15 months. Eggs laid in the fall overwinter in this stage, and hatch in the spring. Some members of this generation of slugs may die in the fall, while others hibernate underground or beneath loose bark. The survival rate of the hibernators depends upon the harshness of the winter. Look in and under rotting logs to find slug eggs, and behind the bark of dying trees to find slug hibernacula.

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How Slugs Eat

9-18-13 slug radula 262No-one needs a description of the damage that slugs can do in a garden, but the exact way in which they do the damage is quite unique. They actually do not have mouthparts as such, nor do they possess teeth as we know them. They, like most molluscs, have a radula, or rasping tongue-like organ with which they procure food. A bit of cartilage, the odontophore, forms the core of the radula. The rest of the radula consists of a band, similar to a conveyor-belt, covered with thousands of tiny tooth-like protrusions called denticles. The band moves over the odontophore, rasping away particles of food and moving them back into the slug’s gullet. The pictured slug was making short work of a mushroom.

ADDENDUM TO YESTERDAY’S POST: After several reader comments and self-reflection, I’ve come to the conclusion that yesterday’s post could well be black bear, not raccoon, vomit. While all I found in the cornfield were signs of raccoons, it was a huge field, and I may have just missed bear sign or the bear may well have visited another field prior to getting sick. The amount of vomit was so large that it would have taken a giant raccoon to have left it. Both of these animals feed voraciously in the fall in preparation for winter — black bears can double their weight prior to denning.

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Slug Mating Behavior

9-2-13 slugs 035Slugs are hermaphroditic, possessing both male and female organs; most species mate, however, with one slug pursuing the slimy trail of another. If a slug is in mating mode, there is a chemical that is present in its slime that conveys this information to other slugs. When two receptive slugs first encounter each other, there can be extensive interaction prior to mating. The pursuer often mouths the tip of the tail of the slug it’s pursuing (see photograph) to confirm that it’s receptive. The pursued slug may shake its tail vigorously to signal that it’s not interested, in which case they go their separate ways. If the leading slug is receptive, however, mating eventually takes place, with sperm being transferred from each slug to the other through penises that extend half the length of their bodies. During this process, the sexual organs are entwined; occasionally, in some species, the organs get stuck. If this happens, one slug gnaws off the other’s penis in a process called apophallation. The penis is not replaced and the slug lives the rest of its life as a female. (The opening you see on the side of the slug is its respiratory opening, or pneumostome.)

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.


A Great Christmas Present!

If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill.  A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!

One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”

In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e  book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”

I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!


Snail and Slug Eggs

Snails and slugs are very similar, except for a slug’s lack of a shell.  Both are hermaphroditic, possessing male and female reproductive organs.  In some species an individual may behave as a male for a while, then as a female. In a few species, self-fertilization occurs. Some species mate and lay eggs in the spring, some in the fall. Most snails and slugs that hatch in the spring can begin egg laying in the fall. The eggs of both snails and slugs are tiny, white or cream-colored, round and laid in roughly one-inch diameter clusters of 30 or so eggs. Look for these clusters under rotting logs, where they are protected from drying out as well as from freezing.  (Remember to place the log back exactly as you found it.)


Naturally Curious wins National Outdoor Book Award

I am delighted to be able to tell you that this morning I learned that NATURALLY CURIOUS won the Nature Guidebook category of the 2011 National Outdoor Book Awards.  I’m honored and humbled by this recognition.   http://www.noba-web.org/books11.htm


Millipede Mystery

This morning I discovered the exoskeletons of nine millipedes clumped together at the top of a rotting stump.  They were covered with slug slime, with said slug still at the scene. Presumably its stomach was full of millipede innards.  If anyone can explain this phenomenon to me, I would be most grateful!


Slug Eggs

If you spend enough time looking under rotting logs, you’re bound to come across the tiny, pearly white eggs of a slug. With the right climate conditions, slugs will mate and lay eggs twice in a summer — once early in the spring, and once in late summer. Thirty to forty days after mating, the female slug lays her eggs under leaves, mulch, or in some other cool and moist location. They will hatch in 10 to 100 days — the length of time slug eggs take to hatch depends upon the temperature – the warmer it is, the faster they hatch.


Eyelash Cup Fungus

Fungi can be divided into two groups – basidiomycetes and ascomycetes.  Basidiomycetes (gilled mushrooms, coral fungus, hedgehog  mushrooms, puffballs, bird’s nest fungus) produce spores on the surface of microscopic cells called basidea.  Ascomycetes (morels, cup fungi, stinkhorns) produce their spores within microscopic sacs (asci).  The slug in this photograph is dining on an ascomycete  — eyelash cup fungus (Scutellinia scutellata), the rim of which bears many stiff, eyelash-like hairs.


Snails and Slugs

Snails and slugs are grouped together as gastropods – a class of Mollusks that includes land, freshwater and sea snails and slugs.  The term “snail” is used for species with an external shell large enough for the soft parts to withdraw completely into it. Those gastropods without a shell, and those with only a very reduced or internal shell, are usually known as “slugs.” We refer to many marine gastropods as seashells, including whelks, conchs, cowries, olives, cone shells, figs and tulips.  While many gastropods are herbivorous grazers, several groups are carnivores, capable of drilling through the skeleton of their prey.