I think lightning elementals are not normally aggressive, which is why they show the green icon. However, nonaggressive mobs can spawn and spontaneously attack as part of a leve. Some examples are the Ravenous Nannygoats (name?) at the end of Dodos and Popotoes (I think) and the Longclaw Galagos summoned from each completed necrologos in Necrologos: Amongst Leaves Most Green, both also at Nophica's Wells.