Observations on the Reproduction, Growth and Longevity of a Laboratory Colony of
Arachachatina (Calachatina) Marginata (Swainson) Subspecies Ovum

Jennifer M Plummer - Department of Physiology,
Electron Microscope Unit, Royal Veterinary College, London.

Below is a very cut down version of a research paper on margies that was sent to me recently. It's from 1975, and contains some very useful information on breeding them.

Thanks to Paul Fischer for the help with the typing (yeah, all the typos *must* be his ;-DD - sorry Paul!!)

Copulation

Although the act of intromission has not been seen, snails have been found in coitus. The following description applies to two snails found in this condition one morning.

Both animals faced in the same direction, both were extended and one, the lower (S1), was almost upside down on the ground. The other (S2) was the right way up, slightly behind and above S1. Each penis made one slow turn round the other, entering it's partner's genital aperture posterior to the emergent penis. After about 10 minutes the penis of the upper snail (s2) was retracted from the genital aperture of S1, followed about 1 minute later by that of S1. The action was a slow pulling apart, followed by a sudden emergence.

Oviposition

Snails about to form an egg chamber tend to enter the soil with the left side of the shell adjacent to, and the head and foot parallel to, the wall of the vivarium. Thus, since the shell sits eccentrically on the body of the animal, the columellar axis of the shell has an angle of approximately 15° to the wall. With the head retracted the snail forces the lip of the shell into the soil raising an arc-like mound of the latter over the body whorl as it penetrates more deeply, the shell thus behaving rather as a plough-share. The depth of the burrow varies with the size of the snail. As a rule, it may be 4-6 inches below the surface at the shell lip, the soil at this stage normally covering the shell. The snail constructs a smooth-walled chamber of oval outline that is usually no more than 1/2 inch from the wall of the vivarium and deposits its eggs in a group only the peripheral members of which are in contact with the soil. When freshly laid the eggs are lemon-yellow in colour but whiten with age. The animal may make its burrow in the course of one night and return to the surface by the next morning. Sometimes it may take two night o achieve the process.

The rate of oviposition can be quite high. It has been observed to completion several times in snails apparently compelled to lay their eggs on the surface. In these conditions it may take from 30 minutes to 2 hours. One snail was observed to lay 6 eggs in 30 minutes. The time from the appearance of the egg in the genital aperture to the final extrusion was approximately 1 minute: 4 minutes later the next egg appeared. The last egg was slower to appear, the total time between its extrusion and that of the penultimate egg being 8 minutes. The head of the snail just protruded from its shell, there was a period of small movements, with contraction waves over the head and with tentacles extending and invaginating. Then the right posterior and anterior tentacles were extended, a bulge in the head wall grew larger, the genital aperture gaped below and behind the bulge (apparently the buccal mass) and the tip of the egg appeared. The latter was now seen to be causing a more posterior swelling of the head beneath the shell. There was a pause of about 30 seconds, the egg was then forced from the genital aperture which shrank behind it and , simultaneously, the right tentacles were swiftly invaginated.

Numbers and sizes of eggs

The number of eggs laid by Archachatina is much smaller than those of the various species of Achatina. In Archachatina the smallest number that we have recorded in a clutch is 3 eggs and the maximum, 16 eggs. The numbers of eggs in 123 clutches have been totaled (1053) giving a figure of 8.6 eggs as the average clutch size. A group of 17 adult African snails purchased in July 1969 started to lay eggs in September 1969 and , by the following July, had laid 43 clutches of eggs (average number per clutch 8.5, range 4-14). The slow start of their breeding together with subsequent performance suggests that these numbers are lower than average. More realistic figures might be a total of more than 400 eggs from 50 clutches.

Young snails show signs of sexual maturity when 9 - 10 months old (prominent genital aperture; exploring other snails). In the next two months eggs are occasionally laid on the soil surface, but are of small size (11-14 mm in length) and the smaller are usually inviable. In a group of 15 maturing snails, 2 inviable eggs were laid at 12 months, then groups of 4, 1, 2, 2 eggs at 13 months some of which hatched. Then the groups of 5 and 6 fully viable eggs were surface laid at 14 months, and at 15 months clutches of 8 viable eggs were found properly buried.

From the measurements of 392 eggs the average length was 20.1 mm (range 10.6-25.1 mm) and the average width was 15.7 mm (range 9.3-19.3 mm). The sizes of eggs laid show a direct relationship to the size of the snail. At any age, on average, a smaller snail lays a smaller egg.

Rate of development of embryo and young snail

The rate of development of the embryo is markedly affected by soil temperature and moisture. The optimum conditions appear to be very damp damp soil at a temperature of 23°C. A long series of investigations in 1956 and 1957, that involved the opening of the eggs at varying times after oviposition, gave an incubation time of 35 - 41 days. The temperature within the vivaria showed the following variations. With an air temperature of 26-28°C the temperature under the foot of a snail on the soil varied from 17.2 to 19.0°C, whilst the soil temperature (one inch below surface) varied from 16.2 to 19.0°C, according to the position in the vivarium. These variations in soil temperature were no doubt responsible for many embryonic deaths. The removal of the vivaria to a constant temperature room, in which the ambient temperature is 23°C and air temperature in the vivaria 26-28°C, has given better incubation results and shorter incubation times.

The feeding rate is of interest when compared to that of older animals. The hatched baby - at a shell length of 24 mm - makes about 23 bites per minute, and adult of 110 mm 20 bites per minute, at 125 mm 17 bites per minute and at 165 mm - 13 bites per minute. Thus, the stroke of frequency varies immensely with the size of the snail.

Hatching of young snails

The late embryo, having ingested the albumen, continues rasp at the egg shell, eroding this and weakening the wall. Occasionally, a hole can be seen in the egg just before the occupant hatches. At this stage, pressure and movement by the embryo cause the egg to split. The embryo continues to rasp the shell, breaking it down and ingesting remarkably large pieces. Examination of the oesophagus of such a baby snail shows this to be distended by relatively huge pieces of shell. At this stage the early hatched animal is a danger to its siblings.

As in other snails, the ingestion of the egg shell appears to be an important element in the development of the young snail and our records suggest that removal of the egg shell delays early growth. This may not be due only to the need for calcium carbonate because natural chalk is usually present in the propagators and vivaria.

The first animal to hatch may tale 24-36 hours to do so and this is normally one of the uppermost members of the clutch. A second animal, in a similar position, may follow in the next 24 hours and all surviving members of the clutch may be hatched within one week. Rarely do all eggs in a clutch hatch successfully and this may be due, at least in part, to the destruction of the lower eggs by upper, earlier hatched snails. The curious feature of this process is the regularity of with which the upper members of the clutch hatch first.

After hatching, the young snails normally remain underground for at least 7 days but this period may extend to 7 - 14 days, particularly if unhatched eggs remain. During this time the young snails continue to grow, increasing their shell lengths by 3-6 mm. Snails at hatching are about 1-2 mm shorter than the egg shell but, when measured, 7 - 10 days later, 1.5 - 4.9 mm longer than the original egg.

During the next 2 - 3 weeks, the young snails may repeatedly burrow into the soil, which appears to be as important to them as it is seen to be in the adults.

Our largest African snail (166 mm when received) reached shell dimensions of 182 by 112 mm. A few (both African and home-grown) have reached 160-170 mm but, in our crowded conditions, snail shells do not usually grow after 4 years. The lip tends to be abraded and the shell may actually shorten, the lip growing thicker, although the snail’s body may grow larger.

The longevity of Arachachatina bred in the college is about 4.5 years. Early death may occur in the third year, most deaths between 3 and 5 years. Thereafter, a few individuals may survive to 7.5 years and the occasional animal reaches 10 years.

Arachachatina has an average increase in shell length of 0.33 mm/day for the first 8 months. This rate slows to approximately 0.2 mm/day at 15 months and thereafter is 0.01 mm/day. This pattern shows similarities to that demonstrated by A. fulica by Kondo (1964): he recognised 3 stages of growth; infant (about 1 month) 0.3 mm/day; adolescence (to about 4 months old) 0.8 mm/day; young adult (4-8 months) 0.5 falling to 0.02; once the snails have reached maturity (324 days) they do not increase in size. Arachachatina has a fairly uniform rate of growth during the first 8 months, unlike A. fulica. Both Arachachatina and A. fulica show a decline in growth rate once the snails reach sexual maturity (9-10 months for Arachachatina).