Under the Wildlife and Countryside Act 1981 (as amended) all shrew species (Soricidae spp.) are listed under Schedule 6 making it an offence to take them using certain methods. Shrews are insectivores and need to feed every 3-4 hours. Long periods of capture in traps can lead to high mortality rates unless certain precautions take place. 
 
In the view of Natural Resources Wales (NRW) the use of unmodified traps to capture shrews would require licensing to cover their intentional trapping. Use of modified traps where there is no intention to capture shrews would not need licensing.  NRW issue licences for scientific, educational, research or conservation purposes, including ringing and marking.  See the “Apply for a permit” section of our website for the relevant application form. 

Modified traps

If you do not need to catch shrews, a shrew escape hole 13mm in diameter can be drilled in the trap nest-box.  A brass washer should be glued around the hole to prevent gnawing by rodents.  The brass washer should be glued to the body of the trap.  There is a small risk of mortality of animals that are too large to escape through the hole and small or juvenile rodents will be able to escape as well as shrews.
 
Some live capture traps allow for the sensitivity of the treadle to be adjusted. In practice this is not sufficient to prevent shrew capture. It is not practical to modify pitfall traps. If pitfall traps are used to catch shrews, food and bedding should be provided as suggested below.   

Unmodified traps - shrew welfare precautions

Appropriate live-traps are those that are designed, set and operated in such a manner as to avoid death or injury. These should be provided with a nest-box containing suitable nesting material.  

  • Trap placement - Ensure traps are stable and that the nest chamber of Longworth traps, where used, is sloped to prevent water running into the bedding. 
  • Food Leave plenty of suitable food in the trap.  Blowfly larvae or pupae (Calliphora spp.; also known as ‘casters’) are best. Use in sufficient numbers to provide 10g per trap. Replace food regularly replaced.
  • Bedding/cover - Leave dry bedding (preferably clean hay) to provide insulation. Cover longworth-type traps with surrounding vegetation or other material, to insulate against extremes of temperature.  Pitfall traps should be covered with a board (larger than the diameter of the trap) raised above the ground on stones to keep rain out
  • Trap inspection - Inspect the trap at suitably frequent intervals. If sufficient food and bedding are left, 12 hourly inspections (dusk and early morning) will be sufficient. If food can not be provided, shrews are likely to die if left for more than 3-4 hours. In such situations visits must be at least every four hours. Note that frequent trap visits will cause disturbance to the habitat and this may affect trapping success. If shrew deaths occur, adjust the amounts of food and bedding or the frequency of inspections, as appropriate.  If despite this deaths continue, suspend trapping and seek advice. Do not trap in very cold or very hot conditions, or where such conditions can reasonably be predicted. The pre-bait door catch should be activated when traps are temporarily out of use.
  • Pitfall traps - When using pitfall traps for invertebrates, frequent inspection will normally be the only reasonable safeguard against accidental shrew deaths. Lids should be placed on pitfall traps when traps are temporarily out of use. 

Further information: 

The Mammal Society booklet Live Trapping Small Mammals – A Practical Guide by J Gurnell and J R Flowerdew (2006). Available from The Mammal Society, 3 The Carronades, New Road, Southampton, SO14 0AA, tel. 023 80237874, www.mammal.org.uk