Not sure exactly what makes the holes, but here is some info on ground burrowing insects in your area.
Ground Bee. Several species of bees build their nests in the ground, but the two of most concern to New Jersey residents and business owners are the usually docile bumble bee and the highly annoying sweat bee.
Image of a NJ bumble bee.The Bumble Bee measures about 3/4 to 1 1/2 inches long. Bumble bees are one of New Jersey's largest bee species and considered a ground bee. Hairy with distinctive black and yellow coloration, bumble bees have a round, robust appearance and buzz loudly when disturbed.
Frequent garden visitors, bumble bees collect pollen and nectar to produce a stored food called "bee bread" that they feed to developing offspring. Living in large social colonies underground, bumble bees can be a problem if they build their nests in garden or lawn areas frequented by people.
Occasionally, these bees invade buildings to nest in soffits or attics. Bumble bees are docile unless provoked or their nest is threatened. They are a problem only when nests are built in trafficked areas.
Image of a halictid bee or sweat bee.Halictid (Sweat) Bees are brightly colored. The halictid or "sweat" bee is the most problematic ground-dwelling bee for humans. Just 1/4 to 1/2 inch long, these tiny bees are a distinctive shiny metallic black and green color.
A persistent summer pest, halictid bees hover around humans, landing on skin to gather sweat droplets. They will sting if startled or swatted, although stings are considered minor. More of a nuisance than a threat, their persistent hovering can be upsetting at outdoor events.
Cicada Killer wasps are known for their monstrous size; up to 2 inches in length, cicada killer wasps often cause alarm. However, these gentle giants are not easily provoked and rarely attack humans.
Feeding primarily on sap and nectar, cicada killer wasps hunt cicadas which they seal into egg cells as food for growing larvae. Solitary insects, these wasps nest underground in dry, soft soil where vegetation is sparse.
http://ipm.ncsu.edu/AG268/html/burrowing_sod_webworm.htm
http://www.asktheexterminator.com/Wasps/Great_Golden_Digger_Wasp.shtml
Their penchant for burrowing in sand traps can make them a nuisance on golf courses. If bothered, their sting is painful.
