Table of contents:
- Economic value
- Size regulation
- Caffeine is bad for slugs and snails
- Likharev. I.M., Victor A.Y. / Slugs of the fauna of the USSR and neighboring countries (Gastropoda terrestria nuda). - L., "Science", 1980. - 438 p. (In the series: Fauna of the USSR. Molluscs. Vol. III, issue 5)
Video: Slugs. Pests. Wrestling. Photo
Slug (slug) is the commonly used name for a number of gastropods that, during evolutionary development, have undergone a reduction or complete loss of the shell (slugs - English; limaces - French; Nacktschnecken - German). Slugs are contrasted with gastropods with a well-developed shell (snails). The slug form independently emerged in several groups of aquatic and terrestrial gastropods, therefore the totality of all species is considered not as a taxon, but as an ecological form. Sometimes slugs that have preserved a rudimentary shell are called semi-slugs (English semislug).
It is assumed that the reduction and subsequent loss of the shell had ecological prerequisites and occurred, for example, during the transition to living in dense thickets of aquatic plants or forest litter. According to another hypothesis, the reason was the lack of calcium necessary for the construction of the shell in the regions where the groups were formed in which the slug form arose. An important consequence of the poor development or absence of the shell is the inability to isolate from the environment when attacked by a predator or unfavorable (for example, arid) conditions.
The body of ground slugs is quite elongated in length, but it is able to change shape due to muscle contractions. Among slugs, there are both "giants", the length of which exceeds 20 cm when moving (Eumilax brandti, Limax maximus, Arion ater), and "dwarfs" - no more than 2 cm (Arion intermedins, Deroceras laeve). Outwardly, slugs have bilateral symmetry. It is disturbed only by the unpaired pulmonary opening located on the right. The skin epithelium separates a large amount of mucus, which prevents the integument from drying out, promotes better sliding on the surface, and also scares off predators.
Like other gastropods, three sections are distinguished in the body of slugs: the head, leg, and visceral mass. The latter, due to the absence of a shell, forms not an internal sac, but a notum (Latin notum - back) spread over the dorsal side of the leg. On the head are contractible tentacles (one or two pairs), on which the senses (developed eyes, organs of tactile and chemical sense) are located. Behind the head, on the dorsal side, there is a mantle with an unpaired pulmonary opening (pneumostomy) leading to the mantle cavity, which functions as a lung. Next to the pneumatic tube is the anus.
© Håkan Svensson
Ground slugs are characterized by hermaphroditism (sometimes sequential) and internal fertilization.
Probably, due to the lack of sufficiently effective devices to prevent dehydration, slugs live only in humid biotopes, such as, for example, the litter of deciduous forests. In the ecosystems existing there, they play an essential role, eating fallen leaves, non-lignified parts of living plants, as well as fungi (including those poisonous to other organisms). Usually slugs give preference to relatively juicy and soft parts of the plant, avoiding areas with hard integuments or fibrous vascular bundles.
The choice of food largely depends on the nature of the vegetation growing in the immediate vicinity of the shelters in which slugs hide during the daytime, as well as on the age of animals - adult slugs willingly eat rougher food than young ones.
Newly hatched slugs feed on the remains of their own eggs and unhatched eggs from the same clutch, and then move on to feeding on humus and decaying plant debris. Only with age does fresh plant food take an increasing place in their diet.
Due to the fact that the activity of slugs most often occurs at night and dusk, they mainly feed at this time. The greatest gluttony of slugs coincides with the period of intensive growth, i.e., before and at the beginning of reproduction, and sharply decreases by the beginning of copulation (connection during intercourse) and during oviposition. During this time, the slugs do not feed.
Representatives of some species are predators and necrophages that eat live soil invertebrates (for example, other gastropods and earthworms) and their corpses.
The feeding intensity of this predator is quite high. So, in summer, one slug 2 cm long on average every day eats one worm 4-6 cm long or an equivalent number of smaller worms.
Slugs have a fairly wide assortment of enemies, including predators. Many vertebrates feed on them, however, there are no specific "slug-eaters" among them. Of mammals, slugs are readily eaten by hedgehogs, moles, shrews and some murine rodents; from birds - rooks, jackdaws, starlings and some seagulls, and from domestic birds - chickens and ducks. Slugs are also a part of the diet of many frogs, toads, salamanders, lizards, and snakes.
Among invertebrates, many insects feed on slugs. They are especially numerous among ground beetles (Carabidae).
Slugs serve as hosts (optional, intermediate, or primary) for many parasites. So, in the digestive tract, liver or kidney of some slugs, several types of ciliates and coccidia are found.
Many slugs are intermediate hosts for a number of digenetic flukes, tapeworms, roundworms, etc. Which, in adulthood, parasitize domestic and wild mammals and birds.
Slugs are hermaphrodites and have both male and female genitals.
After meeting with a partner, they surround each other with sperm, which they exchange through protruding genitals. There are times when the slugs' genitals become entangled with each other, and if the slugs fail to free themselves, they can allow the penis to separate. After that, slugs are able to reproduce only by the female part of the reproductive system.
In the practice of people, the role of slugs is manifested in two aspects: as transmitters of dangerous helminthiases for domestic and game animals and as pests of many cultivated plants.
Transmission of parasitic infestations. Like many land snails, some slugs serve as intermediate hosts for various parasitic worms, the final hosts of which are domestic and wild mammals and birds. Moreover, most often there is no strict specificity between slugs and helminths: the main role is played by the lifestyle of mollusks, which determines the possibility of their meeting and infection with the corresponding phase of the parasitic worm.
Slugs are pests of cultivated plants. Slugs harm a very wide range of grains, vegetables, flowers, industrial crops, as well as citrus and grape plantations. Every year, in many countries, special brochures and bulletins are published, informing about the harmful activities of slugs, giving forecasts for the near future and instructing farmers on how to deal with these pests. Although it has not yet been possible to accurately calculate in all countries of the world the losses that slugs cause annually, it is quite obvious that they are very significant. In addition, harmful slugs differ from many other agricultural pests by their very wide distribution.
Slugs damage a very wide range of crops. Tubers and foliage of potatoes, white cabbage and cauliflower, lettuce, various root crops (foliage and root crop areas protruding from the soil), seedlings and young shoots of many vegetables, beans and pea leaves, strawberries, cucumbers and tomatoes. They do less harm to red cabbage, parsley, garlic, onions, leaves of ripening cucumbers and strawberries.
They cause especially tangible harm to winter wheat and rye, eating both newly sown grains and their seedlings. To a lesser extent, oats and barley suffer from slugs; they practically do not touch spring wheat, flax and buckwheat.
The damage caused by slugs is very characteristic and easily distinguishable from the activity of other pests. In the leaves, they usually gnaw irregularly shaped holes, leaving only the leaf stem and the largest veins intact. On root crops, potato tubers, strawberries, tomatoes and cucumbers, they gnaw cavities of various shapes and sizes, usually widening inward.
In cabbage, they damage not only the surface and surface leaves, but also gnaw deep depressions in the head. In cereal grains, they gnaw both the embryo and the endosperm.
A characteristic feature of such injuries is numerous traces of hardened mucus, heaps of feces and earth. In addition to direct harm, slugs cause indirect harm, contaminating crop products and contributing to their decay, and thereby shortening the snoring period.
Crawling from one plant to another, slugs contribute to the spread of various fungal and viral diseases among agricultural crops - cabbage spot, downy mildew of lima beans, potato late blight. These diseases can cause losses to the farm no less, and often more than the direct harmful activity of slugs. The fact that many of them willingly supplement their diet with fungal hyphae further contributes to the infection of plants with fungal diseases.
Prevention of harm caused by slugs
The very first preventive measure is good gardening. This includes various techniques aimed at improving the quality and structure of the soil, the correct selection of plants, the timeliness of all garden work, maintaining the hygiene of the garden, attracting birds and other useful fauna for the natural control of pests (in this case, lizards, frogs, toads, fireflies and some other beetles, as well as hedgehogs), mutually beneficial neighborhood and crop rotation, and much more. All these measures help to strengthen the plants, because strong plants can resist the attacks of garden pests and diseases much better.
To physical barriersinclude special plastic gutters that are attached around the perimeter of the prefabricated ridges. These gutters are filled with water, which serves as a mechanical barrier for slugs. Any dry, porous materials, as well as fine gravel, crushed shells and eggshells, are unpleasant surfaces for slugs and snails, and therefore are well suited as filler between rows. However, it should be borne in mind that in rainy weather, their effectiveness decreases significantly. The same principle is the basis for the action of a special ecological granular material (Slug Stoppa Granules), which are scattered around the plants and act during the season. Granules create a physical barrier for slugs and snails: they absorb moisture and mucus, dry out the surface of their bodies, making it impossible for pests to move.There are also wide, folded-edge plastic bands available on the market that anchor in the ground around the plants to keep snails and slugs out of the plant. Plant vegetables in raised beds or tubs, tie legumes, tomatoes and pumpkin seeds to supports in time, use clear plastic caps (such as the bottom halves of large plastic water bottles) and film covers for young vulnerable plants - all of which make desirable slug plants physically less accessible.the bottom halves of large plastic water bottles) and film shelters for young vulnerable plants all make the coveted plants less physically accessible to slugs.the bottom halves of large plastic water bottles) and film shelters for young vulnerable plants all make the coveted plants less physically accessible to slugs.
You can pick snails and slugs with your hands in the evening or after rain, so that you can destroy them later (for example, in a strong saline solution or boiling water) or take them somewhere away from gardens and cultural plantings (this option is more humane, but also more laborious). Live slugs and snails should not be placed in a cold compostarium, as adults will lay eggs under favorable conditions. Special traps for slugs and snails are a bowl covered with an umbrella-roof. The trap is installed so that the entrances are at the level of the ground surface. The bowl is filled with beer, fruit juice or other bait (the tasty smell attracts snails and slugs) and the roof prevents rainwater and debris from entering. In the absence of such a trap,Pour the bait into simple bowls from an old unnecessary service and dig in flush with the soil surface on ridges and borders with the most favorite plants of snails. Check and empty traps regularly in the morning.
Distracting maneuvers include old leaves and tops of plants loved by slugs (lettuce, tomatoes, cucumbers, medicinal comfrey, etc.) scattered among the plantings. I personally successfully use this method in a greenhouse, where it helps keep in check not only slugs, but also wood lice: carried away by eating these waste, they no longer crawl to growing vegetables. Periodically, the leaves and pests that eat them can be collected, replacing them with new ones.
Garden centers have self-adhesive tapes made of copper, headbands or copper-clad coverings (trademark Shocka). Contact with copper gives the molluscs a small electrical shock, so they won't want to cross the copper barrier. Headbands with a small battery have recently appeared on the market, which also give snails and slugs a small electrical shock when crossing.
The parasitic nematode Phasmarhabditis hermaphrodit (brand name Nemaslug), which is a biocontrol agent for slugs, is available. The application of the product is possible from spring to autumn (the soil temperature should not be lower than +5 C), it is most effective in wet weather. The advantages of this biological "killer" of slugs are in the duration of action, effectiveness, absolute safety for people and the environment, and convenience and ease of use. Microorganisms should be diluted with water, and then poured over the desired planting from a watering can. Slugs die within a week, one watering is enough for a month and a half, according to the manufacturer. The disadvantages lie in the short shelf life of the product (it must be used within 3-4 weeks from the date of release, since microorganisms are "preserved" in a living state),and the need to keep it cold at all times.
The plants that slugs and snails do not like and try to avoid include, first of all, garlic, as well as many (but far from all!) Aromatic plants (lavender, sage, santolina, thyme, rosemary, laurel, etc.), which they never touch. Garlic is used by manufacturers of special phyto-infusions that repel slugs. Infusions of garlic, bitter pepper, and mustard are famous folk remedies for fighting slugs and snails.
© Daniel Ullrich
On sale are granules of metaldehyde (sold in Russia under the brand names Groza and Meta) - an effective agent that attracts and kills slugs and snails. The package says that the product is poisonous to pets and people if it gets into their digestive system. The high toxicity of the agent is also evidenced by the fact that Bitrex (the most bitter substance) is added to it to scare away animals and children if they suddenly decide to eat beautiful blue granules. Manufacturers claim that when used correctly, the product is completely harmless to people, pets and the environment, but warnings are often found in the gardening press. Metaldehyde should be stored and handled with great care. Wash vegetables and herbs especially thoroughly if you have used metaldehyde in your garden.I scatter blue granules exclusively around ornamental plants (hosta, delphinium, lofant, etc.) and only in early spring, when young leaves emerge from the ground and are especially vulnerable to slugs and snails.
Caffeine is bad for slugs and snails
Caffeine, in the form of an aqueous solution, applied to the soil or to the leaves of plants, repels and kills slugs and snails, presumably by destroying their nervous system. This conclusion was made by Hawaiian scientists from the US Department of Agriculture as a result of a series of experiments. According to the observations of scientists, a 1 or 2 percent solution kills even large individuals (although at the same time discolors the leaves of some plants), and a 0.1 percent solution introduces pests into confusion, accelerating the heartbeat, and scares them away from plantations. To get a 0.1% caffeine solution, you can, for example, dissolve a double dose of instant coffee in a cup of water.