  We have developed an algorithm to identify solar spicules in the first ever
systematic survey of on-disk spicules exclusively using Mg II spectral
observations. Using this algorithm we identify 2021 events in three Interface
Region Imaging Spectrograph (IRIS) data sets with unique solar feature targets
spanning a total of 300 minutes: (1) active region, (2) decayed active
region/active network, and (3) coronal hole. We present event statistics and
relate occurrence rates to the underlying photospheric magnetic field strength.
This method identifies spicule event densities and occurrence rates similar to
previous studies performed using H{\alpha} and Ca II observations of active
regions. Additionally, this study identifies spicule-like events at very low
rates at magnetic field intensities below 20 G, and increasing significantly
between 100 and 200 G in active regions and above 20 G in coronal holes, which
can be used to inform future observation campaigns. This information can be be
used to help characterize spicules over their full lifetimes, and compliments
existing H{\alpha} spectral capabilities and upcoming Ly{\alpha} spectral
observations with the Solar eruptioN Integral Field Spectrograph (SNIFS)
sounding rocket. In total, this study presents a method for detecting solar
spicules exclusively using Mg II spectra, and provides statistics for spicule
occurrences in the Mg II h line with respect to the magnetic field strength for
the purpose of predicting spicule occurrences.
