Ground 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.
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.
Slugs 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.)
Common 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.)
Slugs 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.
No-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.
Slugs 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.)