Not really gardening, but today my class where at playtime and they found some black wriggling maggot type things. they were under the soil about 0.5-1cl down and where about 2-3 cm long and quite fat. they were localised in a group and really really grim. I feel really ill thinking about them - YUCK. But also I am strangly fasinated (would also score brownie points with my class) - what could they be?