Snail Reproduction

How does the Banff Springs Snail Reproduce?

Each Banff Springs Snail has both male and female reproductive organs – they are hermaphrodites. In theory, a single snail could therefore reproduce on its own. While this is a common type of reproduction in freshwater snails and allows some species to quickly increase in numbers, there are consequences to this life style. Scientists have found that when snails reproduce on their own, their offspring are not as fit or healthy as are those offspring which have two parents.

The Banff Springs Snail lays eggs, as do most other kinds of snails. In other physid snails, 10 to 12 oC is usually the minimum trigger for the snails to start reproducing but because the Banff Springs Snail lives in thermal springs, they can reproduce throughout the year and we have seen the clear, fat, banana-shaped egg capsules year-round in some springs. Because the egg capsules are clear and only about 5 mm long by 2 mm wide, they are difficult to see. They are usually found right at the air-water interface attached to the floating mat of bacteria and algae, or sticks, and other objects. We have even seen them attached to other snail shells. They most likely require atmospheric oxygen to develop, given the low levels of dissolved oxygen in the thermal spring water.

Based on observations in aquaria, Banff Spring Snail egg capsules contain around 12 individual eggs. It takes about 6 days for the eggs to develop and tiny, miniature snails with shell lengths less than 1 mm to hatch. Once they grow to about 3 mm in shell length, they can then begin laying their own eggs. In aquaria where the snails were being fed, they reached reproductive size in about 9 weeks. In the wild, we expect growth rates to be slower. We also suspect they only live for about a year or so, because when we put adult-sized snails into aquaria, they lived for another 10 or 11 months.

Banff Springs Snails and their egg capsules attached to a board walk post at the Cave and Basin National Historic Site.

Banff Springs Snails and their egg capsules attached to a board walk post at the Cave and Basin National Historic Site.

Close-up of 4-day old Banff Springs Snail egg capsule, taken through a microscope with black and white film (10 December 2000). There are eight individual eggs within the egg capsule, with one egg (bottom left) containing two embryos (twins)!

Close-up of 4-day old Banff Springs Snail egg capsule, taken through a microscope with black and white film (10 December 2000). There are eight individual eggs within the egg capsule, with one egg (bottom left) containing two embryos (twins)!

Next Page – Why is the Banff Springs Snail Endangered?