Six weeks ago, Patricia Flanagan of Hillsborough's Swallow Hill Farm got a very rare treat, the birth of twins on the farm. 

Shadow and Buttercup are extremely rare as only about a dozen pairs of alpaca have survived of the 150 or so twin births over the last 20 years, Flanagan said. Most twins do not survive the 335 days of a normal pregnancy to even be born.

Patricia and John Flanagan have been raising alpacas since 2007 and have 23 of them on their 8-acre farm on Montgomery Road. The farm originally raised horses and later sheep.

"I learned spinning and knitting, but I was highly allergic to the wool," Patricia Flanagan said. 

A farmer once told Flanagan how alpacas' fiber is hypoallergenic. Flanagan decided to test it and put her face in the animal's coat and experienced no reaction. That changed their farm forever.

The twin cria or baby alpacas were only eight pounds at birth with a normal cria weighing about 15 pounds. Both of the babies are doing well and are growing rapidly. Alpaca mom, Kizzy, was previously shown on the "Today" show and dad, Commodore, has won blue ribbons.

The Flanagans run a store at the farm, selling yarns and knitted items made from alpaca fiber. Lighter than wool and hollow, fiber is considered warmer than wool. The alpaca are sheared once a year in May and the females have one cria a year.