Using data from the Wide-field Infrared Survey Explorer we studied the mid infrared 3.4 \mu m ( W1-band ) and 4.6 \mu m ( W2-band ) flux variability of \gamma -ray emitting blazars .
Our sample consists of 460 flat spectrum radio quasars ( FSRQs ) and 575 BL Lacertae ( BL Lac ) objects .
On intra-day timescales , the median amplitude of variability ( \sigma _ { m } ) for FSRQs is 0.04 ^ { +0.03 } _ { -0.02 } mag and 0.05 ^ { +0.03 } _ { -0.02 } mag in W1 and W2 bands .
For BL Lacs we found median \sigma _ { m } in W1 ( W2 ) bands of 0.04 ^ { +0.01 } _ { -0.02 } ( 0.04 ^ { +0.02 } _ { -0.02 } ) mag .
On long timescales , for FSRQs we found a median \sigma _ { m } of 0.44 ^ { +0.28 } _ { -0.27 } mag and 0.45 ^ { +0.27 } _ { -0.27 } mag in W1 and W2 bands , while for BL Lacs the median values are 0.21 ^ { +0.18 } _ { -0.12 } mag and 0.22 ^ { +0.18 } _ { -0.11 } mag in W1 and W2 bands .
From statistical tests , we found FSRQs to show larger \sigma _ { m } than BL Lacs on both intra-day and long timescales .
Among blazars , low synchrotron peaked ( LSP ) sources showed larger \sigma _ { m } compared to intermediate synchrotron peaked ( ISP ) and high synchrotron peaked ( HSP ) sources.The larger \sigma _ { m } seen in FSRQs relative to BL Lacs on both intra-day and long timescales could be due to them having the most powerful relativistic jets and/or their mid infrared band coinciding with the peak of the electron energy distribution .
BL Lacs have low power jets and the observational window too traces the emission from low energy electrons , thereby leading to low \sigma _ { m } .
In both FSRQs and BL Lacs predominantly a bluer when brighter behaviour was observed .
No correlation is found between \sigma _ { m } and black hole mass .