REPRODUCTION
Most freshwater snail species are separately sexed. Males fertilize the female through direct copulation, and then females attach their eggs directly to firm, clean substrates such as a rocks, logs, or aquatic vegetation, usually in shallow water. Egg clutches can contain two to 300+ eggs, depending on the species, and can take several hours or weeks to be deposited. Females can lay eggs singly, in pairs, in a circular pattern, or in a large line several eggs across and several inches in length. Because freshwater snails occur across a variety of freshwater habitats, they have adapted different reproductive strategies. There are basically three different modes of reproduction commonly used by freshwater snails.
For species that lay discrete clutches, the eggs are deposited over a period of one to three months, usually in the late winter and early spring. Larger, older females tend to lay more eggs per clutch. Warmer water temperature plays an important role in egg production, but day length also may be an important factor. Individual eggs are small, a little larger than 1/75 inch in diameter. The eggs may take one to five weeks to hatch depending on water temperatures. The warmer the water, the faster the eggs will hatch. A juvenile snail is about 1/100 inch at hatching, but rap- idly grows its first year to several hundred times its birth size. Rapid juvenile growth in shell size to over 1/4 inch wide in the first year is not uncommon.
Another reproductive strategy of some operculate species is for females to birth live young. In reality, an egg hatches inside the female and the juvenile snail grazes in a special pouch inside the mother's body. After a few weeks of feeding, a juvenile snail about 1/4 inch in length crawls outside the mother's body. Female snails can produce several eggs simul- taneously, and up to a dozen small juvenile snails can be inside the female during the summer and fall months. Like other operculate snails, these species have separate sexes and the male uses a modified tentacle as a penis. Juvenile snails emerge from the female fully functional and ready to feed.
Other species of freshwater snails have yet another mechanism for reproduction. For these species, each snail contains both male and female reproductive systems, and all individuals can lay eggs. Eggs are laid in large, clear gelatinous clutches that can easily exceed 1/4 inch in diameter. Individual eggs and juveniles are generally larger than those of other snails at hatching. The total number of eggs is dependent on clutch size, but the clutches of some species contain over 50 individual eggs. As long as the food is abundant, these species generally produce eggs continuously from the late spring into the early fall. Not surprisingly, these species are widespread, commonly encountered, and rarely of conservation importance. However, these snails are a very important and abundant food for many crayfishes and fishes.
