Decollate Snail

The decollate snail is native to North Africa and the Mediterranean Region. It was inadvertently introduced into Southern California. They are thought to have spread from this point into more states overtime. Since it was introduced yet doesn't seem to be causing harm, it does not appear to be considered invasive in the United States at this time. Decollate snails can be spread readily in container plants and soil that are moved through human means. They are a carnivorous snail, mainly consuming animal matter. But are overall omnivorous in their feeding habits [3].

Taxonomy

Kingdom	Animalia
Phylum	Mollusca (mollusks)
Class	Gastropoda (gastropods)
Order	Stylommatophora (Air breathing snails + slugs)
Family	Subulinidae (Small, tropical snails)
Species	Rumina decollata

Adult decollate snail on a leaf. [3]

Land Snail Overview

All continents have land snails, they are especially prevalent everywhere in Eastern North America, where there are more than 500 native species. They live mostly in leaf litter of forests, old fields, and wetlands. They can also be found in more disturbed habitats such as active gardens and fields, river banks, suburbs, and even cities. The term ‘land snails’ includes snails and slugs, which have no obvious shell, they're shell is actually inside them. Most land snails feed upon a wide variety of organic material. But it is mainly consistent of green or dead herbaceous plants, rotting wood and fungi, bark and algae. They also consume empty snail shells, sap, animal scats and carcasses, and even rasp on limestone rock or cement [4].The radula (like in many mollusks,) has a rasping tongue as a mandible, they can use to ‘rasp’. It is full of horny teeth made of chitin and is used for scraping off particles of food from underneath [6]. Carnivorous snail species attack nematodes and other snails. Carnivorous snails are where the decollate snail lands on the feeding scale. Predators of land snails include invertebrates such as parasitic mites, nematodes, flies, beetle larvae, adult beetles, millipedes, and other snails like the decollate. Some other larger predators include salamanders, turtles, shrews, mice and other small mammals. Even birds, especially those who are ground-foragers. Both shelled snails and slugs can generally be categorized as decomposers. [4]

Identification

To identify a decollate snail, their spiraling shell is pinkish brown, elongated irregularly unlike most other land snails. It is tapered toward the end. Young snails can have a more pale-colored lighter brown shell. The shell can grow up to 1-3/5 inches (40 mm) long and 5/8 inch (14 mm) in diameter. When the shell grows, the tip of the shell breaks off and older whirls of the shell are dropped. Only four to seven whirls are retained in older snails, as the rest are discarded. Younger snails may retain up to 10 whirls of the shell, as they have not dropped those whorls yet. Their antennae, head, and foot are blackish to dark olive-gray. The decollate snail eggs are pale white in color, and are buried in the topsoil. They can be found in clusters or singularly [3]. To further identify them, we can look at the order they are classified in, Stylommatophora. Stylommatophora includes air-breathing land snails and slugs. Snails in Stylommatophora have lost their gills, and have an air-breathing organ with a lung on its roof. The two things that all Stylommatophora share are a long pedal gland placed beneath a membrane and retractile tentacles. Their eyes can also be found on the tips of two long tentacles, in this case, the decollate snails eye stalks. [7]

Habitat and Distribution

Decollate snails are native to North Africa and the Mediterranean Region. They were introduced into Southern California in the 1960s. They now occupy irrigated sites in Central and Southern California. They are considered introduced and not invasive, because they are non-native but do not seem to be causing harm. Because this snail is a burrowing species and the eggs and snails occur in topsoil, the snail can be spread easily by humans in plants and soil that are moved, leading to them being found in more states than California [3]. Currently, they are introduced in the United States, Bermuda and Mexico. It is widespread, but localized, in the Sun Belt from California east to Florida and north along the Atlantic coast to Pennsylvania [5]. As for their native habitats, In Europe they live in dry and open habitats, and prefer shady habitats in Portugal, between plants and under stones, or buried in the soil. They dislike sandy and loamy soils. In North Africa snails can be found up to 10 cm deep inside the soil, and under stones. Yet they are rarely found in the root systems of shrubs [1].

Adult decollate snail playing in leaf litter. [1]

Behavior

The decollate snail lives only in and on litter and soil. They climb only to escape heavy rain or irrigation water. This is unlike most common land snails, like garden snails that will climb trees and other objects. They are active mostly at night and during overcast or rainy weather. During the day they hide in leaf litter on the ground and in the top one inch of soil in the US [4]. They are a predatory snail, in the US feeding on common garden snail species. Although they are opportunistic and can be considered omnivores, feeding on new sprouts, old leaves within the soil, and fallen bruised fruit as well [5].

Life Cycle

These snails are hermaphrodites, having both female and male parts. They are self-fertile, but commonly mate with another decollate before laying eggs. But if they cannot find a mate, they do not need one to lay eggs. They are reproductively mature about 10 months after hatching from an egg. Female decollate snails can lay about 200 eggs per year and up to 500 eggs during their lifetime. Their eggs are round and whitish in color, and are laid in the topsoil. The eggs have a brittle shell and are 1/12 inch in diameter. They are laid singly or in loose clusters in a depression in the topsoil, and hatch within 10-45 days [3]. They are laid inside between May and October, adult snails estivate (go into a dormant state) inside the soil 1-3 months covering their eggs. Creation of the first whorls begins in the second month, and the snails hibernate mostly inactively inside the soil during this time, then as growth and decollation continues, they become more active [2].

Ecosystem Role

Since these snails don't move far over their lifetime, they can be excellent indicators of site history and site conditions. Land snails have a high calcium demand, and are sensitive to calcium availability in their habitat, a lack of snails might be a sign of low calcium in an environment, which could be a indicator for other problems or mineral deficiency [4]. They can also play a role in shredding and transforming organic substances. Decollates combine their slime with particles from the ground and improve the structure of the soil, therefore improving the soil structure. Many snail species are specialized in feeding on unusual materials, and when these snails are eaten by decollate snails, those difficult to digest materials can then be contributed to the decomposition and transformation of these substances These snails are an important source of food for other animals. They feed birds, hedgehogs, moles, amphibians, reptiles, ground beetles, spiders and more [6].

Human Relevance

While considered introduced in the US, some argue decollate snails may have an anthropogenic benefit here. Some people say they have value in controlling the brown garden snail as a pest in agriculture, and this is considered to outweigh the decollate snail's ‘minor pest’ attributes in California. Although they are still only found in cultivated habitats with frequent irrigation [5]. Although studies have shown that they are not consistently effective, introducing the decollate snail can reduce brown garden snail populations to insignificant levels in 4 to 10 years [3].

References

1] AnimalBase :: Rumina decollata species homepage. (2013). . http://www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBase/home/species?id=1293.

2] Cadmium in soils and groundwater: A review - PMC. (2020). . https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7147761/.

3] Decollate Snail / UC Statewide IPM Program (UC IPM). (n.d.). . https://ipm.ucanr.edu/natural-enemies/decollate-snail/.

4] Mollusks : Carnegie Museum of Natural History. (2005). . https://www.carnegiemnh.org/science/mollusks/landsnailecology.html.

5] snail eating snails. (n.d.). . https://entnemdept.ufl.edu/creatures/misc/gastro/snail_eating_snails.htm.

6] Snails. Germanfactsheet.pdf. (n.d) https://agresearch.montana.edu/wtarc/producerinfo/entomology-insect-ecology/EasternHeathSnail/GermanFactSheet.pdf

7] Classification. (n.d.). . http://bioweb.uwlax.edu/bio210/f2012/ravenscr_patr/classification.htm.