Harleysville Mutual Insurance Co. is going to assume a Houston, Texas, company’s “Write Your Own” flood business, effective November 1.

Pennsylvania-based Harleysville Mutual will obtain Delta Lloyds Insurance Co. WYO flood business, while Delta General Agency Corp., through its more than 500 retail flood agents, will represent Harleysville, the companies said in a statement.

Delta General will continue to provide training, servicing and marketing support for flood insurance to those agents.

Terms of the transaction were not disclosed.

“Since entering the WYO flood program in 1999, our goal has been to become a major participant in this fee-based segment of the insurance business,” said Michael L. Browne, Harleysville’s president and chief executive officer, said in a statement.

Through a combination of acquisitions and organic growth, Harleysville Mutual has increased its WYO flood book at a 14% compound annual rate since 2005, Browne said.

“The Delta Lloyds transaction will increase our size and scale in this niche,” Browne said. “More importantly, our agent partners tell us that flood insurance is a valuable part of the portfolio of products that they can offer to their clients.”

Delta Lloyds, a participant in the WYO flood program since 1984, wrote about $13.5 million in direct WYO flood premiums in Texas in 2008. Based on flood premiums alone, Delta Lloyds is the 23rd largest WYO flood carrier nationally and the 7th largest in Texas.

Harleysville wrote about $82.6 million in direct flood premiums nationwide in 2008. Based on flood premiums alone, Harleysville ranks 11th nationally and 17th in Texas.

WYO flood claims are 100% reinsured by the federal government’s National Flood Insurance Program.