Introduction: How Snails Move

As discussed in the Basic Biology section, apple snails can move both in and out of the water due to having a gill-like structure and a lung.  They can move both horizontally along the substrate and vertically up and down plant stems.  Apple snails are also able to move up and down the water column by regulating their buoyancy (Burky and Burky 1977).  All sizes of snails can float freely, and this may be a way for snails, especially hatchlings, to disperse (Darby pers. comm.).   

Distances Moved

Apple snail movement patterns have been examined by Darby et al. (1997; and 2002) using radio telemetry [for information on telemetry and radio transmitters, see the Sampling section on Telemetry].  Snails moved an average of 14.0 ± 1.4 (SE) meters per week and as much as 83 meters per week during a March-June marsh study, and an average of 7.8 ± 1.5 meters per week and up to 42 meters per week in lake habitat in a winter study (Darby et al. 2002).  The distance traveled was generally proportional to the time interval between observations.

 

Movement along a Gradient? 

Movement rates were not affected by water depth or temperature (Darby et al. 2002).  However, the tendency to move was affected by depth. When water depths dropped below 10 cm, snails tended to stop moving (see Figure 2 below).  The greatest tendency to move towards deeper water (along a positive depth gradient) occurred when snails were in waters 10-20 cm deep.  Conversely, when encountering water depths ≥ 50 cm, snails tended to move towards shallower water.  Based on the two studies, apple snails do not appear to move along temperature or dissolved oxygen (D.O.) gradients. 

The 10 cm threshold level may be due to impeded movement due to an accumulation of vegetation and suspended materials (organic debris and periphyton) as the water level drops, or it may be a behavioral response to imminent drying.  At this water depth, snails settle in place, and as water continues to recede they become stranded in dry down conditions.

 

Although apple snails have the ability (as discussed above) to move sufficient distances to avoid dry downs, Darby et al. (2002) has found them unable to find deep water refuge during these events.  For example, on Lake Kissimmee, 10 snails moved along a positive depth gradient 14 times to no ultimate advantage; 8 of the 10 snails later became stranded, one died before it would have been stranded, and one made it to deeper water.  Of the total 31 snails monitored on Lake Kissimmee, only one escaped the drying event and moved to deeper water.  Of the 11 snails in the Blue Cypress Water Management Area (BCWMA) that were originally in the area that went dry, three were found in deep water at the end of the study.  Darby et al. (2002) concluded that as the areal extent of a dry down increases, the number of snails stranded likely increases proportionally.  Stranded snails must then deal with dry down conditions (see Section on Dry Down Survival).

 

Female vs. Male Snail Movements (Distance and Pattern)   

The use of radio transmitters on snails led to information on differences in movement distances and patterns between males and females.  [These data were originally reported in Darby et al. (1997); they are being incorporated into a manuscript for journal publication.]  Over an 18 week monitoring period in BCWMA, females moved 10-20 meters per week on average, with no obvious change over time.  Average weekly distances traveled by males, however, did change over time and peaked during late March-early May.  Patterns of movement were also examined, with differences observed according to gender.  Movement patterns of male snails tended to be more linear and of greater distances, while female movement patterns tended to be more centralized.

Gender differences in distance and pattern, along with M:F ratio data from wire funnel trap sampling (see Sampling section on Funnel Traps), suggest that snail movements during the spring and early summer are driven by snail reproductive activity (Darby et al. 1997).  Male snails appear to follow female snails into traps, but “baiting” a trap with a female snail did not lead to male captures.  Males appear to seek female snails for mating, likely by following female mucous trails.  Chemoreception and trail-following as directional guides for movement have been documented for other snails (e.g., Chase and Boulanger 1978; Cook 1979; Tomiyama 1992). 

For further information on movements related to water depths and gradients, see Darby et al. (2002); for more information on movements related to gender, see the upcoming journal article (citation to be provided at later date).

Literature Cited 

• Burky, K.A. and J.A. Burky.  1977.  Buoyancy changes as related to respiratory behavior in an amphibious snail, Pomacea urceus (Muller), from Venezuela.  Nautilus 91:97-104.

• Chase, R. and C.M. Boulanger.  1978.  Attraction of the snail Achatina fuliica to extracts of conspecific pedal glands.  Behavioral Biology 23:107-111.

• Cook, A.  1979.  Homing in Gastropoda.  Malacologia 18:315-318.

• Darby, P.C., P. L. Valentine-Darby, R.E. Bennetts, J.D. Croop, H.F. Percival and W.M Kitchens.  1997.  Ecological studies of apple snails (Pomacea paludosa, SAY).  Final Report Submitted to the South Florida Water Management District and St. Johns River Water Management District.  St. Johns River Water Management District Special Publication SJ98-SP6.  Palatka, FL. 

• Darby, P.C., R.E. Bennetts, S.J. Miller, and H. Franklin Percival.  2002.  Movements of Florida apple snails in relation to water levels and drying events.  Wetlands 22(3): 489-498.

• Tomiyama, K.  1992.  Homing behaviour of the giant african snail, Achatina fulica (Ferussac) (Gastropoda; Pulmonata).  J. Ethol. 10:139-147.