In spring, when the Roman snails are awake from hibernation,
the mating season begins. [RN]
|
In spring, when the Roman snails are awake from hibernation, the mating season begins. [RN] |
In spring, when the Roman snails have been awake from hibernation for some time, it becomes time for mating. Depending on the weather and other environmental conditions, mating time may last until the end of June. Only until then the juveniles will have enough time to prepare for hibernation so they are able to survive winter.
Roman snails, and with them most terrestrial snail species, are hermaphrodites. They have male, as well as female organs in one collective genital apparatus. This organ system not only contains sexual organs in the narrow sense of the word, but also various auxiliary organs, that have respective tasks in different periods during mating.
What advantage does being a hermaphrodite give to a Roman snail? Because of its proverbial slowness the snail needs much time to move in a very small area. So the chances to meet a mating partner are too low to divide them even further by two sexes to choose from. Terrestrial pulmonate snails (Stylommatophora), such as the Roman snail, on the other hand, have double mating chances, because in principle, they can mate with any snail of the right species they encounter. Besides, during copulation, Roman snails do not act as either male or female, but simultaneously as both.
A Roman snail's mating process takes place in several phases, which go from an attraction phase over an extensive courtship until finally the copulation itself.
Picture
series: Roman Snails Mating.
 Attraction sometimes passes the borders of species. Helix lu- corum (left) and pomatia (right). Picture: Arno Brosi. |
The encounter of two Roman snails ready for mating is not purely incidental. Like many other terrestrial snails, they as well have a gland located at the head, producing an olfactory sexual attractant. Those attractants are also used by other snail species among the helicid snails, such as banded snails (Cepaea).
As a consequence incidentally two snails of entirely different species may feel attracted
and try mating. Between snails of different species, that attempt must, of
course, remain unsuccessful.
: Falkner,
G. (1993)
Inter-species mating between a
Roman snail (Helix pomatia) and a grove snail (Cepaea nemoralis).
Pictures:
Christian Gagelmann.
Mating between Roman snails and their relatives, though, are certainly possible, but will not yield any fertile offspring. Bastardization between closely related snail species may, however, lead to the development of new species, as it occurs among the family of door snails (Clausiliidae).
The courtship among Roman snails is a very interesting thing to witness: Both snails begin by raising their heads and putting their flat foot soles against each other. They touch each other with tentacles and lips while they are swaying gently. As a prelude to the actual copulation this courtship process may last as long as twenty hours. The copulation itself will take a much smaller fraction of time.
During the courtship possibly a dart may be applied, one snail stinging it into the mate's foot. This dart has been called love dart, as its application obviously is in direct connection with courtship or mating.
The pricked snail becomes visibly more excited and active, sometimes it also returns the favour by jabbing a love dart into the mate's body. A Roman snail's love dart can become as long as 7 to 11 mm and consists of a four-edge blade on one and a crown on the other end. In idle state with this crown the dart sits on a papilla in the dart sac. To use the dart, the snail pushes out the interior of the dart sac, thrusting the dart into the mate's body. After separation from the papilla, the dart remains stung in the body.
Though it is called a dart, in many languages also an arrow, the Roman snail's love dart is neither thrown nor shot, there is no distance of free flight! Instead it is thrust into the mate's body, more like a dagger, than a dart (see picture on the right!). Sometimes, though, the love dart also misses its target. Than it may come to rest on the mate's body without penetrating it, but it can also happen that one of the two mates is hurt.
It is not in every mating process, that a love dart is applied. To be precise, that is not even possible! Roman snails mate, whenever possible, but the replication of a love dart needs sometimes more time, than remains between two mating encounters.
Research has found out, that the application of a love dart does not at all only influence a snail's behaviour.
By means of the love dart a secretion is injected, that is
produced by the finger shaped glands in the genital apparatus. This secretion
contains hormones, that influence certain parts of the genital apparatus and
that way improve the reproductive chances of the snail that applied the dart.
: Koene, J.; Chase,
R. (1998).
The exact effects of the hormone secretion transferred by the love dart are described together with the respective organs of the genital apparatus.
 It so happens that snails are of a very different enthusiasm during courtship… [RN] |
After the long and extensive courtship there may be several attempts on copulation. It may so happen that the readiness to mate between two snails is very different, so that the copulation attempts may look more like a wrestling match.
When finally both snails managed to find a suitable position, they actually perform copulation. Both penises are entwined and inserted into the mate's vagina. The union successfully completed, both snails stay as they are.
Now, a sperm packet, a so-called spermatophore, is produced in either snail's body and afterwards filled with sperm cells.
This spermatophore is almost 10 cm long and is roughly shaped like a thread. Even after it was positioned in the mate's genital apparatus, the tail still looks out of the snail's genital opening.
This is why the two snails remain motionless for a certain time after completing of the copulation: The spermatophore's application in the mate's genital apparatus must be supported; an early interruption of the union may disrupt the spermatophore and thus render useless the hours of toil included in a standard snail courtship.
It is only now that both snails separate. Only little time later they may meet again with other potential mates. A part of the sperm cells just received, however, will be stored in a special sperm pouch. Those sperm cells may then well manage to fertilise egg cells, though they will have to compete with sperm cells of other mating partners also stored in the same pouch.
Fertilisation, though, only happens, when it is time to lay eggs. That finally will happen, provided the environmental conditions are favourable and there is a place where the eggs can be deposited in a special hole in the ground.