Hedgehogs, Slugs and Slug Pellets

Do hedgehogs eat slugs?


Yes. Hedgehogs eat slugs although other prey forms a larger proportion of their diet, such as earthworms, caterpillars and beetles. This is based on the analysis of the stomachs of 137 dead hedgehogs.  Hedgehogs consume a wide range of prey including dead animals and eggs they find as they forage.


Can hedgehogs help control slugs?


Yes.  Frequent  visits  by hedgehogs  to your garden should help reduce slug numbers although never eliminate them altogether. This will help minimise reduce slug damage to sensitive plans. Remember that not all slug species are pests  – the three main ones that damage plants are the grey field slug, the garden slug and the keeled slug.


 Are slug pellets a threat to hedgehogs?


Three different chemicals are used in slug pellets sold in the UK.  The most common is metaldehyde (labelling on packs always states the active ingredient).  Some  products contain methiocarb and others ferric phosphate.   All three are used on farms and in gardens.


Slug pellets contain other chemicals as well as the one targeting slugs.  Slug pellets can only be used if the active ingredients has been approved by EU and UK authorities.  The EU and UK approval processes only cover the safety of active ingredients not the entire product.  These approvals are based on laboratory tests of several  mammals (eg rats, guinea pigs and dogs) carried out by and submitted by the applicants seeking approval. The main toxicity tests are for acute toxicity that results in 50% of the test animal dying.  Long term, sub-lethal harm can be missed.


In terms of acute toxicity to mammals , methiocarb is 8 times more toxic than metaldehyde  and about 150 times as toxic as ferric phosphate.  However, none of the tests quoted include hedgehogs and toxicity varies greatly between species. Dogs are attracted to metaldehyde and acute poisoning cases have been reported.


Slug pellets usually come in hard, often blue, pellets, which are softened in wet conditions . The blue colouration makes them less attractive to birds.


Hedgehogs would have to eat a lot of pellets to get a lethal dose. Chronic exposure via eating poisoned slugs could occur although there is a very little research in this area,


Could slug pellets harm hedgehogs in other ways?


There are two other ways in which slug pellets could harm hedgehogs. The first is by reducing their food supplying by killing slugs.  Methiocarb is also known to be toxic to earthworms as well as slugs. Earthworms are a more import food source for hedgehogs than slugs.


The second is through hedgehogs eating slugs that are already poisoned with slug pellets and hedgehogs could get a dose every time they eat a dead or dying slug in an area that had been treated.




What are the alternatives for controlling slugs?

Slugs can be a major pest on farms and gardens. There are a number of alternatives to chemical pest control.  The main one is to build up population of natural predators such as hedgehogs, frogs and toads and birds, such as song thrushes . Such biological control will never eliminate slugs altogether but can keep numbers below  a damaging threshold.   Human being can also control numbers by collecting and killing slugs after dark using a torch


However in wet years slugs can multiple faster than they can be eaten and in such circumstances traps, barriers and parasitic worms can be used to keep numbers down.  Beer traps are effective by attracting slugs which drown in the beer.  Barrier methods involve placing a dry substance around the plant you want to protect. These should be renewed if they get wet.    Egg shells, grit, sheep wool and soot (if available) have all been used in this way. It is also claimed that copper tape deters slugs but the evidence for this is thin.


Another controversial approach is using coffee grounds.  Caffeine is a slug repellent when applied direct but evidence  that mulching with coffee grounds (for instance)  has the same effect is lacking. Coffee ground can be mixed with a mulch and provided a useful amount of nitrogen to feed plant .  Applying caffeine (in say coffee) direct to plants or slugs is technically illegal in the EU and UK because there is no approval for caffeine as a pesticide.


On a farm scale,  many garden techniques would not be practical. However, providing and maintaining habitats for slug predators such as hedgehogs, beetles, frogs and toads and song thrushes will serve to provide some level of control over this pest.  Some soil cultivation will help expose eggs to the air causing them to dry out or expose them to predator.  Crop rotation also helps by avoiding slug prone cropping every year.   The practice of minimum cultivation or zero tillage, when crops are drilled into the stubble of the previous crop. has increased slug problems in the UK and made establishing the new crop more difficult unless slug pellets are applied. Metaldehyde is detected in water destined for drinking water as it readily washes off field and down field drains into rivers which are abstracted for public supply.  Metaldehyde is not easy to remove from water prior to it entering public supply and the emphasis is on timing treatment to avoid periods of heavy rain and only applying pellets when the risk of slug damage is high.


Use of the least toxic slug pellets based on ferric phosphate is an option of last resort but use should be limited in order to minimise any toxic effects and to avoid slugs getting resistant to the product.