, ▁most ▁Gl ens ▁develop ▁a ▁robust ▁pre y ▁drive ▁and ▁will ▁readily ▁go ▁for ▁verm in ▁such ▁as ▁r ats , ▁so ▁they ▁need ▁to ▁be ▁well - social ized ▁with ▁other ▁animals ▁when ▁young — part icular ly ▁with ▁small ▁household ▁p ets ▁that ▁they ▁might ▁mistake ▁for ▁quar ry , ▁such ▁as ▁c ats ▁and ▁rabb its . ▁ ▁Gl ens ▁often ▁do ▁well ▁at ▁Earth dog ▁tri als , ▁Bar n ▁H unt , ▁and ▁in ▁ag ility . ▁Although ▁not ▁typically ▁strong ▁sw imm ers ▁due ▁to ▁their ▁short ▁legs ▁and ▁dense ▁body , ▁some ▁Gl ens ▁can ▁work ▁in ▁water , ▁and ▁others ▁have ▁been ▁trained ▁to ▁her d ▁and ▁drive ▁sheep ▁and ▁cattle . ▁ ▁Rel ations hip ▁to ▁other ▁bre eds ▁Though ▁the ▁exact ▁origin ▁of ▁the ▁Glen ▁of ▁I ma al ▁Ter rier ▁is ▁lost ▁to ▁history , ▁some ▁say ▁that ▁the ▁bre ed ▁may ▁be ▁related ▁to ▁the ▁So ft - Co ated ▁Whe aten ▁Ter rier , ▁another ▁Irish ▁ter rier ▁bre ed ▁( in ▁fact , ▁some ▁sources ▁claim ▁all ▁Irish ▁ter rier ▁bre eds ▁to ▁be ▁derived ▁from ▁the ▁So ft - Co ated ▁Whe aten ) ▁and / or ▁the ▁Ker ry ▁Blue ▁Ter rier . ▁The ▁" low - sl ung ▁h ounds " ▁in ▁the ▁Glen ' s ▁her itage ▁are ▁sometimes ▁held ▁to ▁be ▁for er unn ers ▁of ▁the ▁P B GV ▁and ▁the ▁source ▁of ▁the ▁d war f ism . ▁Though ▁the ▁Glen