To find the sum of the given arithmetic series, we need to find the number of terms and then use the formula for the sum of an arithmetic series.

The first term, a = -2
The common difference, d = 4 - (-2) = 6
The last term, l = -18

To find the number of terms, we can use the formula:

l = a + (n-1)d

Substituting the given values:

-18 = -2 + (n-1)(6)

Simplifying:

-18 = -2 + 6n - 6
-18 + 2 + 6 = 6n
-16 = 6n
n = -16/6
n = -8/3

Since the number of terms cannot be negative or fractional, we can round up to the nearest whole number. Therefore, the number of terms is 3.

Now, we can use the formula for the sum of an arithmetic series:

Sn = (n/2)(a + l)

Substituting the given values:

S3 = (3/2)(-2 + (-18))
S3 = (3/2)(-20)
S3 = -30

Therefore, the sum of the arithmetic series -2 + 4 + -6 + 8 + ... + -18 is -30.