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Sourcing 13LGS

by Dana Merriman last modified Feb 20, 2020 12:52 PM


13LGSs are not difficult to live-trap from the wild in their natural range of central North America (see for a nice map, as well as some other useful visuals about this species' biology).  

Originally denizens of short-grass prairies, 13LGSs have apparently expanded their natural range thanks to human activity that removed forests in favor of grasslands. They tolerate a good bit of human activity, but abandon cultivated ground.  Favorable modern habitats include pastures, golf courses, athletic fields, cemeteries, and lawns.  Since 13LGS are considered a pest by many, some property owners/managers may be glad to have them gone. 

Before you decide to trap: 

  1. Check with your state's Department of Natural Resources to determine if a scientific collector's permit (or similar) is required for trapping this species.  In Wisconsin, for example, 13LGSs are not a species of concern (indeed, the internet is rife with ways to exterminate these "vermin"), so no state permit is currently needed. Similarly, no federal permit is currently needed. 
  2. Check with your state's Health Department about possible zoonoses carried in local populations of 13LGSs.  While this information is subject to change, currently according to the CDC: Bubonic plague IS a concern when trapping 13LGS out west; wild rodents are NOT considered carriers of rabies; and squirrels are NOT considered carriers of hantavirus.  In 2019, some 13LGSs in Illinois were reported to carry Lyme disease
  3. Check with your IACUC regarding your facility's acceptance (or not) of wild-caught animals. Anti-parasite treatments will be called for, and you and your staff will need special training in wildlife research. Unlike lab rats and mice, 13LGS will bite, so certain PPE will be needed. Squirrels are also very fast and agile, so a soft net is a must in every squirrel room. 
    1. Regardless of age at capture, wild 13LGS need to be treated immediately with flea spray using a formulation safe for cats.  
    2. Upon return to the facility, a subcutaneous dose of ivermectin is warranted. 
  4. Contact a lab that has experience with wild-caught 13LGSs to get husbandry protocols before you write for IACUC approval.  We can help, but we aren't the only ones. Search the current peer-reviewed literature to see if there's a 13LGS expert near you.

Many research projects stipulate MALE subjects.  The 13LGS sex split at birth is 50:50 spread across a few litters but, in the wild, females routinely outnumber males. If you need males, it may be most efficient to capture pregnant females.  Litters average 8 pups but 10-12 are not unusual.  Fortunately, newly wild-caught pregnant 13LGS females make great mothers, given the right care, despite their sudden change in circumstances. Gestation is 4 weeks.  In the wild, pups are weaned at 6-10 weeks old (larger litters nurse longer), but thriving captive-born pups can be weaned as early as 5 weeks old.   

  • It is difficult to sex 13LGS pups until they are ~8-9 weeks old. Genital pigment and anogenital distance are NOT reliable indicators. Karyotyping may be called for, if that's a concern for your project. 

Trapping is best done when it is sunny and warm, putting these small mammals as close to their thermoneutral zone as possible.  Retreat to their burrow is a major factor in thermoregulation, whether it be cold or hot out. 

The time of year for strategic trapping is crucial because this is a hibernating species with a short active season. Latitude and snow cover (i.e. weather events) impact the actual extent of the active season.  In recent years in Wisconsin, we've had 80 degree days or blizzards in mid-April that have jumbled up what is described below as "typical". 

  • April: Fertile males and newly-emerged females coming into estrus.  If you want pregnant females, WAIT.
  • May: Males are still fertile, but most females are pregnant OR have recently given birth.  To trap pregnant but NOT lactating females, IN GENERAL:
    • trap around May 5 in southern WI, 
    • trap around May 15 in central WI, and 
    • trap around May 25 in far northern WI.  
  • June: Females are nursing young and the males are going out of reproductive mode.  Trapping females is not advised.  
  • July: Recently weaned young of the year appear, identified by their smaller size (75 g vs. 150 g).  Juveniles are quite numerous at first, but it is estimated that 90% will not make it to or through hibernation.  If you want juveniles, trapping in mid-to-late July would be the best strategy.  
  • September: adults are fully in fall transition and may begin to hibernate already, so much of what is still active will be juveniles.  

If you want further information on capture methods or husbandry of newly-caught wild 13LGS, there are some published papers on this topic, but you may also contact me directly:  merrimad (at) uwosh (dot) edu



A captive breeding 13LGS Colony in Wisconsin has served the research community since 2007.  Inquire about available animals at merrimad (at) uwosh (dot) edu



Labs that already use 13LGSs may be willing to share tissues. Consider checking the recent peer-reviewed literature to identify compatible investigators. 



For years there was a USDA-approved trapping company operating out of Illinois (TLS Research), but that company is no longer in business. 



Occasionally one finds a 13LGS available through "exotic animal breeders" and the like.  



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by Dana Merriman last modified Feb 20, 2020 12:52 PM